7.1 Lesson 7 Introduction

Welcome to Lesson 7

Turning on the hot water tap is one of the most routine actions in your daily life, but behind that simple gesture lies a constant exchange of energy. Most homes rely on storage tank water heaters that work around the clock to keep water hot, ready for whenever you need it—even when you're asleep or away. While this convenience ensures you never have to wait for warm water, it also means your heater is constantly consuming fuel to maintain that temperature, contributing to the 12% of home energy use we discussed earlier. In this lesson we will learn about the different types of hot water heaters available on the market and compare their costs and efficiency. In this section, we'll move beyond the basic physics of heating water to understand how real-world usage, heater settings, and household habits directly impact energy consumption and cost. By connecting the formula Q = mcΔT to actual appliance operation, you'll learn how small changes in how you use hot water can lead to significant savings.

Lesson Objectives

Identify the 6 main types of water heaters
Calculate the energy consumption required to heat water
Compare upfront cost vs. annual energy use of different types of hot water heaters
Evaluate the life cycle cost of different types of hot water heaters

mxw142 Fri, 03/06/2026 - 12:31

7.2 Water Heaters

Think about all the places you use hot water in your life. Every time you shower, or wash your hands you are using energy to make that water hot. In this lesson we will learn about the most common types of hot water heaters available on the market.

Types of Water Heaters

In this lesson, you will learn about the main types of Water Heaters on the Market today. Here is a quick rundown of those types.

Type	Quick Description
Storage Tank	Heats and stores water in an insulated tank (most common)
On-Demand / Tankless	Heats water only when you need it—no storage
Heat Pump (Hybrid)	Moves heat from the air into water (like a fridge in reverse)
Tankless Coil	Uses your home's boiler to heat water on-the-fly
Indirect	Uses a boiler + separate storage tank for higher efficiency
Solar	Uses sunlight + collectors to heat water (with backup system)

Costs of Water Heaters

Just like other appliances, there are two costs associated with water heaters - initial purchase price and operating costs. Water heaters typically last for about 7-13 years, after which they need to be replaced. Also, each month, you pay for the fuel you use. An energy-efficient model could save hundreds of dollars in the long run in the energy costs and may offset the higher initial purchase price.

It can be compared to automobile mileage—some cars get 15 miles to a gallon, while other, more efficient, vehicles can go 30 miles or more on a gallon of gas. In the same way, some water heaters use energy more efficiently.

One should buy an energy-efficient water heater and spend less money each month to get the same amount of hot water. In this lesson, we will be recalling our "Life Cycle Cost Calculations" that we learned back in Lesson 5 to compare the actual cost of heating hot water in our home.

Typical Water Use at Home

The table below shows typical water use for various purposes at home.

Typical Water Use
Use	Gallons per use
Shower	7-10
Bath (standard tub)	15-20
Bath (whirlpool tub)	35-50
Clothes washer (hot water wash, warm rinse)**	7-25
Automatic dishwasher **	3-5
Food preparation and cleanup	5
Personal (hand-washing, etc.)	2

Energy costs increase with water temperature. Dishwashers require the hottest water of all household uses, typically 135ºF to 140ºF. However, these devices are usually equipped with booster heaters to increase the incoming water temperature by 15ºF to 20ºF. Setting the water heater between 120ºF and 125ºF and turning the dishwasher’s booster on should provide sufficiently hot water while reducing the chances for scalding.

**This is for modern (2020s) based appliances. If you are using an older dishwasher or clothes washer, your hot water usage may be much higher!

mxw142 Fri, 03/06/2026 - 12:32

7.3 Energy Required for Water Heating

You use hot water for many things in your daily life, including cooking and bathing. Remember back from Lesson 6, heating water accounted for about 12% of the energy use in your home. So now we are going to calculate how much energy it takes to heat each gallon of water. The amount of energy required depends on what temperature you started with and what temperature you want the water to be, which is our temperature difference. All substances have a heat capacity, which is like it thermal inertia, which tells us how it resists temperature changes. This is why some substances seem to get hot quicker (like a metal spoon versus a wooden spoon.)

For water, the heat capacity, Cp, is 1 BTU/lb ^oF.

In other words, it takes 1 BTU of energy to raise a pound of water one degree Fahrenheit. (In metric this is 4.184 J/g ^oC. or 4.184 Joules of energy to raise one gram of water one degree Celcius.)

So the only thing left to know is how much a gallon of water weighs. For reference, one gallon weighs 8.3 pounds. One liter of water weighs 1000 grams.

To calculate the Heat Required to heat water, use the equation below:

$Q = m \times C_{p} \times ΔT$

Where …

$m$ = mass of water heated

$C_{p}$ = the heat capacity of water (1 BTU / lb ºF)

$ΔT$ = temperature difference

Important Point Icon

Remember to make your units of measurements consistent. Since C_p is measured in pounds, your mass of water heated should be measured in pounds as well. Thus, if you only know the number of gallons, you must convert it into pounds. One gallon of water = about 8.3 pounds, so multiply number of gallons by 8.3 to determine the weight in pounds.

Example 1

It is estimated by the United States Department of Energy that a family of four, each showering for 10 minutes a day, consumes about 700 gal of hot water a week. Water for the showers comes into the home at 55ºF and needs to be heated to 120ºF.

To calculate the heat required, determine the variables:

m = mass of water heated = 700 gallons = 5810 lbs
C_pis the heat capacity of water = 1 BTU/lb ºF (given)
ΔT = temperature difference = 120 ºF – 55 °F

Heat energy required to heat 700 gal can be calculated as follows:

Heat Required = 5,810 lbs × 1 BTU/lb ºF × (120 ºF – 55 ºF)
Heat Required = 5,810 lbs × 65 ºF
Heat Required = 377,650 BTU/week

The heat requirement for one year is :

377,650 BTU/Week × 52 Weeks/Year = 19,637,800 BTU/year
or 5,755 kWh/year. (Remember 1kWh = 3412 BTUs)

Assuming that the natural gas costs $3.5 /MMBTU (1 MMBTU = 1,000,000 BTU) and electricity costs 0.145 per kWh, the annual natural gas costs would be $68.73 while annual electric costs would be $834.54. Clearly, electric hot water is much more expensive than natural gas.

Example 2

Estimate the % energy savings of an electric water heater that heats 100 gallons of per day when the temperature is set back at 110° instead of 120°F. The basement is heated and is at 65°F. The life of the water heater is expected to be about 10 years. Use an appropriate cost for electricity and compare the operating expenses.

Heat required (BTU) = m × C_p × (Temperature Difference)

Where C_p is the heat capacity of water (1 BTU/lb ºF) and m is the mass of the water (Assume 1 gal has 8.3 lb of water and the 3,412 BTU = 1 kWh)

Solution:

Energy required for heating the water to 120°F:

$= m \times C_{p} \times ΔT$

$= \underset{m}{\underset{︸}{\frac{100 gal}{day} \times \frac{8 .3 lb}{gal}}} \times \underset{C_{p}}{\underset{︸}{\frac{1 BTU}{lb °F}}} \times \underset{ΔT}{\underset{︸}{(120 - 65) °F}}$

$= \frac{100 gal}{day} \times \frac{8 .3 lb}{gal} \times \frac{1 BTU}{lb °F} \times (120 - 65) °F$

$= 45,650 BTU/day$

In a year the energy required is:

$\frac{45,650 BTU}{day} \times \frac{365 days}{year} = 16,662,250 BTUs per year$

In a 10-year period, the energy required is 166,622,500 BTU which is equal to 48,834 kWh.

$166,622,500 BTU \times \frac{1 kWh}{3,412 BTU} = 48,834 kWh$

Operating cost over its lifetime is:

$\frac{48,834 kWh}{1} \times \frac{$0 .09}{kWh} = $4,395.06$

Energy required for heating the water to 110°F:

$= m \times C_{p} \times ΔT$

$= \underset{m}{\underset{︸}{\frac{100 gal}{day} \times \frac{8 .3 lb}{gal}}} \times \underset{C_{p}}{\underset{︸}{\frac{1 BTU}{lb °F}}} \times \underset{ΔT}{\underset{︸}{(110 - 65) °F}}$

$= \frac{100 gal}{day} \times \frac{8 .3 lb}{gal} \times \frac{1 BTU}{lb °F} \times (110 - 65) °F$

$= 37,350 BTU/day$

In a year, the energy required is:

$\frac{37,350 BTU}{day} \times \frac{365 days}{year} = 13,632,750 BTUs per year$

In a 10-year period, the energy required is 136,327,500 BTU which is equal to 39,995 kWh .

$136,327,500 BTU \times \frac{1 kWh}{3,412 BTU} = 39,995 kWh$

Operating cost over its lifetime is:

$\frac{39,955 kWh}{1} \times \frac{$0 .09}{kWh} = $3,595.95$

Estimated % Energy Savings:

$$4,395.06 - $3,595.95 = $799.11 savings$

$\frac{$799.11}{$4,395.06} = 18.2% savings$

mxw142 Fri, 03/06/2026 - 12:35

7.4 Storage Tank Hot Water Heaters

The most common type of water heaters use a storage tank type. If you have this type of hot water heater, it is often found in the basement or tucked away in a closet. This about how silly it is to keep your hot water tank in the basement, where it usually coldest in the home. This means the hot water heater has to work harder to heat up the water. Traditionally, they were located in the basement in case of leak, for easy clean up.

Storage or tank-type water heaters are relatively simple devices and by far the most common type of residential water heater used in the United States. They range in size from 20 to 80 gallons, and can be fueled by electricity, natural gas, propane, or oil.

Parts of an Electric Hot Water Heater

Diagram of a water heater with numbered components including valves, anode, elements, and thermostats. — Electric Hot Water Heater

Parts of a Gas Hot Water Heater

Diagram of a water heater with labeled components including flue, cold water valve, dip tube, temperature and pressure relief valve, and burner. — Gas Hot Water Heater

How a Gas Hot Water Heater Works

When you turn on a hot water faucet or use hot water in a dishwasher or clothes washer, water pipes draw hot water from the tank. To replace that hot water, cold water enters the bottom of the tank, ensuring that the tank is always full. Depending on the type of fuel that is used, either electrical heating elements or a natural gas burner is used to heat the water.

Please watch just the first two minutes of the following video about gas hot water heaters.

How Do Gas Hot Water Heaters Work? (8:18)

How Does a Gas Hot Water Heater Work?

Transcript: How Does a Gas Hot Water Heater Work? (8:18)

Hi, I'm Vance and welcome to Repair and Replace.

Your water heater works hard to give you a steady supply of hot water.

In this episode we'll learn how gas water heaters work and then we'll look at some of the differences between standing pilot and power vent models.

Lets begin.

How it Works

A standard water heater burns gas to heat the water stored inside the insulated tank. When hot water is used, cold water enters through a dip tube and fills the bottom of the tank. The gas control valve uses a built in thermostat to monitor the water temperature. When the thermostat senses the cold water, it opens up the main gas valve. Air is drawn from below the tank and mixes with the gas. The main burner ignites, and the exhaust fumes rise up through the flue vent. The burner continues to heat the water until the set temperature is reached.

Protection

The temperature and pressure relief valve is by far the most important safety device in water heaters. If the pressure or temperature inside the tank gets to high, the relief valve will open and release water, preventing the tank from exploding. Additionally every water heater has a drain valve at the bottom which can be used to flush the tank of sediment. If too much sediment builds up it will act as an insulator reducing the efficiency. This is why its best to flush the tank once a year during regular maintenance. Regardless of the type, all water heaters need protection against corrosion and rust. The tank is coated with a thin glass lining but it doesn't always cover 100% of the tank. Also the glass can become cracked, exposing more of the tank walls. On the top of the tank sits the anode rod. Like a lighting rod the anode attracts the corrosive elements in the water, sacrificing itself to protect the tank. If the anode dissolves completely, or if the rod is completly incased in calcium, then the corrosive elements will start attacking the exposed metal. Most anode rods will last 4 - 6 years, but this depends on the pH and purity of the water. This is why its best to check the anode rod during regular maintenance. All water heaters have a relief valve, drain valve and an anode rod, but ignition and venting is different in Standing Pilot, and power vent models

Standing Pilot Water Heaters

Older homes will generally have a standing pilot water heater, with an atmospheric vent. They use a small pilot flame that burns continuously, igniting the main burner when heat is needed. This is the standard design that has been used for decades and is easily identified by the metal exhaust pipe. Since its the pressure from combustion that pushes the exhaust upwards, these heaters must be vented vertically. Any restriction in the airflow might cause backdrafting, which can extinguish the pilot flame. These tanks are generally replaced with newer standing pilot models, since connecting to the existing vents keeps replacement costs low. Standing pilot water heaters will either use a conventional or an electronic gas valve.

Conventional Gas Valves

Conventional gas valves are powered by a thermocouple. The thermocouple sits in the pilot flame, and generates a small amount of electricity when heated. About 20 - 30 millivolts. This produces enough electricity to power the gas valve. The thermocouple also acts as a safety switch. If the pilot light goes out, then the thermocouple will cool down, the voltage will drop and the gas valve will shut off. This prevents unburnt gas from being released into your home.

Electronic Gas Valves

Electronic valves require more power as they have additional circuitry and diagnostics. These valves are powered by a thermopile, which is a pile of thermocouples bundled together. When heated by the pilot flame thermopiles generate around 600 - 750 millivolts. Electronic valves will also flash an error code when something goes wrong. And these are often listed on the valve.

Common Problems

Now if the pilot isn't staying lit, then it's most likely a problem with the thermocouple or thermopile. Alternatively it could be an issue with the thermal cutoff switch. The thermal switch protects against overheating. If the temperature in the combustion chamber gets too high, the thermal switch will shut off the gas valve. The thermocouple, thermopile and thermal switch can all be tested. You can learn more in the troubleshooting videos linked in the description.

Power Vent Water Heaters

Unlike standing pilot heaters, power vent models don't rely on atmospheric pressure. Instead they use a draft inducer blower to push the exhaust through the vent. This makes them useful in newly constructed homes as they can be placed virtually anywhere. When the thermostat detects cold water, the draft inducer pulls fresh air into the burner. The pressure switch then verifies that there's enough airflow for combustion. Next the hot surface ignitor heats up and ignites the burner. The flame sensor monitors the burner to confirm that there is a flame. The burner runs until the water in the tank reaches the set temperature. After the burner shuts off, the inducer will stay on for several minutes to purge the system of exhaust gases.

Common Problems

Power vent water heaters are similar to high efficiency furnaces. If any one of the safety switches trips or is faulty, then the water heater will shut down. It will attempt ignition several times before going into a hard lockout. The water heater will use flashing lights as codes to describe the source of the error. It's best to check your manual to see what these codes mean. You can learn more in the videos linked in the description. Hopefully this has given you a better understanding of how water heaters work. For more troubleshooting on water heaters, furnaces and appliances then subscribe to our channel. And if you need help, you can call or visit an AMRE location to talk with our knowledgeable staff. Thanks for watching.

Credit:How Do Gas Hot Water Heaters Work? AMRE Supply. YouTube. Accessed June 5, 2026

Electric water heaters are generally less expensive to install (purchase price) than gas-fired types because they don't require gas lines and vents to let the combustion products out of the house.

Storage tank-type water heaters raise and maintain the water temperature to the temperature setting on the tank (usually between 120°–140°F). Because the water is constantly heated and kept ready for use in the tank, heat energy can be lost even when no faucet is on. This is called standby heat loss. These standby losses represent 10 to 20 percent of a household's annual water heating costs. Newer, more energy-efficient storage models can significantly reduce the amount of standby heat loss, making them much less expensive to operate.

Advantages and Disadvantages of Tank Water Heaters

Advantages and Disadvantages of Tank Water Heaters
Advantages	Disadvantages
Cheapest hot water heater on the market. Easy to install Can be run on a variety of fuels (electric, gas, propane, fuel oil) depending on the need.	Highest operational costs of all water heaters High stand by losses as water is constantly being reheated while in tank. High energy use even when not in use.

To Learn More

How to Maintain an Electric Water Heater (4:46)

How to Maintain an Electric Water Heater | This Old House

Transcript: How to Maintain an Electric Water Heater (4:46)

Intro

[Music]

[Kevin O'Connor] Did you know that 40% of households make their hot water using electricity?

[Richard Trethewey] Really? I thought it was 41.

[Kevin] All right, I rounded.

[Richard] Well, it makes good sense. In many parts of this country, electricity is the most cost effective way to make hot water. Many people don't have a choice of gas or oil, and sometimes you just can't get the flu products up and out of the building into the chimney or outside.

[Kevin] So an electric water heater is not going to have a flu coming up out through the center.

[Richard] You can put it just about anywhere.

[Kevin] Okay.

[Richard] So I thought today we' do a little Anatomy lesson.

[Kevin] I love your cutaways.

[Richard] Now this is a unit came back from a recent project. Electric water he like this is a glass lined steel tank.

[Kevin] And that glass lining helps preserve this tank from rusting.

[Richard] And keep it from rusting. Okay, cold water comes into the tank through the top right here, but it goes inside of this dip tube and introduces itself into the bottom of the tank.

[Kevin] And the hot water naturally wants to be up here in the top half of the tank.

[Richard] That's right, and that's where it leaves the tank, right through this tapping right here, and goes out to the faucets.

[Kevin] Gotcha.

[Richard] Okay, now inside the tank there's also this Rod. This is called an anode rod.

[Kevin] Remember you telling us about this. This also helps preserve the tank because this wants to corrode before the glass line.

[Richard] Very good. That's a sacrificial anod Rod. Now electricity comes in here, 220 volts comes down into this point right here, and now it comes down and either goes to one of two elements.

[Kevin] So these elements are actually what makes the water hot?

[Richard] That's right. There's one at the top and one right down here at the bottom.

[Kevin] Okay.

[Richard] Okay. So what brings these units on is a thing called a thermostat, and it sits right here. And let me show you what it looks like close up. This this thing sits and touches the wall of that steel tank.

[Kevin] You're actually reading the temperature of the inside.

[Richard] So you set it for about 125. You don't want to go much higher. You don't want to scald anybody.

[Kevin] Gotcha.

[Richard] Okay, now when it says I need to heat up the tank, it sends voltage, 110 volts, to each of these wires to this element right here. Now always the first element to come on is the top element.

[Kevin] Yup.

[Richard] It will do what it can, and once that's satisfied, you'll now bring on the lower one.

[Kevin] Okay, so good Anatomy lesson. What typical problems can I expect with an electric water heater?

[Richard] People complain about no hot water, don't they? Don't overlook the obvious. It could be that there's no power coming from the electrical circuit panel.

[Kevin] Mhm.

[Richard] But if you prove that you are getting power into the water heat and you still don't have either element on, I would look at this. Right above the thermostat is a thing called an ECO, an emergency cut off right here, and so this is designed to act as a safety.

[Kevin] Yeah.

[Richard] That you set this for 125, and if this ever didn't work and you kept on heating up the water, this would feel the temperature. Once it got to 170, it would pop this button out and knock out both the elements. Can only get it on by resetting right here.

[Kevin] So you're saying if both elements are out, that's what would cause no hot water. What if one element were out?

[Richard] Well, you're going to have one of two symptoms. You're either going to have lukewarm hot water, you're just getting it's just not enough, and that means one of the elements is out. Or you can have the complaint of I get plenty of hot water but not enough anymore, and that means it might just be that the lower element is out. The top one is only heat in the top, in this case 40 gallons.

[Kevin] We go through that.

[Richard] That's right, and then it goes to cold.

[Kevin] Gotcha. Okay, so how do I determine which element is broken, and can I fix them?

[Richard] Well, you can't fix them, but you can test them, and you can replace them.

[Kevin] Okay.

[Richard] They make replaceable elements. There's a couple of choices. One is made out of copper, and one is made out of stainless steel.

[Kevin] Mhm.

[Richard] You can see this has one Loop right here. This one has one Loop but as much longer, and it actually is doubled back on itself. Now I prefer this one for two reasons. One is stainless steel, and the other is this larger surface series should make it last longer.

[Kevin] Okay, great. So how do we test it? Obviously here's an old busted up one. How do we know if this is working or not?

[Richard] If there was a lot of minerals on this element, you kept on putting voltage in here, it could make this element break, and that means there would be no continuity, no ability for current to travel through this element.

[Kevin] How do we know?

[Richard] So we're going to test it with this. This is a continuity tester, so we if the light comes on, it means that we're it's good, and that one is good.

[Kevin] Okay, so that's good.

[Richard] Okay, if I was in the field, I would want to make sure I turned off the electricity to the water heater first. Then I would want to disconnect the electrical wires.

[Kevin] So this thing I'm looking at right here is actually the back end of this element.

[Richard] Exactly, facing just like that.

[Kevin] Gotcha.

[Richard] Okay.

[Kevin] So we disconnect everything.

[Richard] So we'll test this one.

[Kevin] And again it's working. Let's say it wasn't.

[Richard] Okay. Well, they make a wrench, a socket wrench, that is made expressly for changing this element that fits on here.

[Kevin] Great.

[Richard] You would go counterclockwise.

[Kevin] We obviously going to want to drain the tank once we get this.

[Richard] Yeah, you learn actually when the water shoots out, you know it was time, you were too late.

[Kevin] All right, let get that out.

[Richard] That goes there.

[Kevin] I'll work that.

[Richard] That was a little dunky.

[Kevin] Yeah, that one's kind of beat up.

[Richard] All right, and the new one, one comes with a gasket as well. The other tip I will tell you is if you go to the trouble of draining the tank and putting in the new element, you should also put in a new thermostat and Eco at the same time.

[Kevin] Great, Richard. Now 40% of America knows what's going on in their basement.

[Richard] That's right.

Credit: How to Maintain an Electric Water Heater. This Old House. YouTube. Accessed June 5, 2026

mxw142 Fri, 03/06/2026 - 12:37

7.5 Demand Water Heaters

Demand Water Heaters do not have storage tanks, so there is no standby heat loss from the tank, and energy consumption is reduced by 10 to 30 percent depending on your hot water usage. Demand water heaters are available in propane (LP), natural gas, or electric models.

In these types of water heaters, cold water travels through a pipe into the unit, and either a gas burner or an electric element heats the water only when needed. With these systems, you never run out of hot water. However, the flow rate is limited by the outlet temperature.

The appeal of demand water heaters is the elimination of the tank standby losses, the resulting lower operating costs, and the fact that the heater delivers hot water continuously, so you will never run out!

How a Demand Water Heater works

How Tankless Water Heaters Work (1:08)

How Tankless Water Heaters Work

Transcript: How Tankless Water Heaters Work (1:08)

Conventional hot water heaters heat and store hot water 24 hours a day. That constant heating and reheating of water is an enormous waste of energy and money.

A tankless water heating system is the energy efficient way to meet all your hot water needs. These compact units can produce and supply endless hot water at a constant temperature.

Once a hot water faucet is turned on, cold water enters the tankless system. The system starts operation mode. The burners ignite as the cold water is heated in the heat exchanger. The hot water then flows to the fixtures.

When the hot water faucet is shut off, your tankless system goes into standby mode. You save energy by heating water only when you need it.

Replace your inefficient conventional water heater with one of our tankless systems today, and start enjoying the convenience of endless hot water and greater energy savings. We're the area's specialists and tankless technology. Call today, and we'll provide expert answers to all your questions and help you determine which tankless system is perfect for your needs.

The future in hot water heating is here today.

Credit: How Tankless Water Heaters Work. American Vintage Home. YouTube. Accessed June 5, 2026.

Typically, demand heaters provide hot water at a rate of 2 to 5 gallons per minute. This flow rate might meet the requirements of a household's hot water needs as long as the hot water is not needed in more than one location at a time (e.g., one cannot shower and do the laundry simultaneously). To meet hot water demand when multiple faucets are being used, demand heaters can be installed in parallel sequence.

Although gas-fired demand heaters tend to have higher flow rates than electric ones, they can waste energy even when no water is being heated if their pilot lights stay on. However, the amount of energy consumed by a pilot light is quite small. Thus, in most cases, gas demand water heaters will cost less to operate than electric water heaters.

Demand water heaters cost more than conventional storage tank-type units and often have more complicated installation. On demand hot water heaters are sized by how much hot water it can produce per minute (gallons/minute). This can be anywhere from 2-5 gallons/minute, so you need to consider how much hot water use your home will need at the same time. The more hot water the unit produces, the higher the cost.

Advantages and Disadvantages of Demand Water Heaters

Advantages and Disadvantages of Demand Water Heaters
Advantages	Disadvantages
Compact in size Virtually eliminates standby losses Wastes less water because warm water is provided immediately where it is used (no need to wait for water to warm up) Provides unlimited hot water as long as it is operated within its capacity Equipment life is longer (20 years vs. 10-15 years for tank-type heaters) than tank-type heaters because they are less subject to corrosion	Demand water heaters usually cannot supply enough hot water for simultaneous uses such as showers and laundry. Unless your demand system has a feature called modulating temperature control, it may not heat water to a constant temperature at different flow rates. That means that water temperatures can fluctuate uncomfortably—particularly if the water pressure varies wildly in your own water system. Electric units will draw more instantaneous power than tank-type water heaters. If electric rates include a demand charge, operation may be expensive. Electric demand water heaters require a relatively high electric power draw because water must be heated quickly to the desired temperature. Make sure your wiring is up to the demand. Demand gas water heaters require a direct vent or conventional flue. If a gas-powered unit has a pilot light, it can waste energy.

mxw142 Fri, 03/06/2026 - 12:38

7.6 Solar Water Heaters

The most efficient type of hot water heater is a solar hot water heater. These can sometimes be called solar domestic hot water systems. This uses the energy from the sun to heat water for use in your home. The collector is usually mounted on the roof of the home.

A roof mounted solar water heater.

Credit: Thermodynamic Panels Installed by KVDP from Wikimedia (Public Domain)

Collector Types

Batch collectors, also called Integrated Collector-Storage (ICS) systems, heat water in dark tanks or tubes within an insulated box, storing water until drawn. Water can remain in the collector for long periods of time if household demand is low, making it very hot. A tempering valve is your protection from scalding at the tap. The tempering valve mixes in cold water to decrease the water's temperature before it's delivered to the tap. Batch collectors are incompatible with closed-loop circulation systems. Thus, they are generally not recommended for cold climates.
Flat-plate collectors typically consist of copper tubes fitted to flat absorber plates. The most common configuration is a series of parallel tubes connected at each end by two pipes, the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box, and covered with tempered glass.
Flat plate collectors are typically sized to contain 40 gallons of water. Two collectors provide roughly half of the hot water needed to serve a family of four.
Evacuated tube collectors are the most efficient collectors available. Each evacuated tube is similar to a thermos in principle. A glass or metal tube containing the water or heat transfer fluid is surrounded by a larger glass tube. The space between them is a vacuum, so very little heat is lost from the fluid.
These collectors can even work well in overcast conditions and operate in temperatures as low as -40°F. Individual tubes are replaced as needed. Evacuated tube collectors can cost twice as much per square foot as flat plate collectors.

Source: Energy Star: How It works- Solar Water Heaters

Circulation Systems

Direct systems circulate water through solar collectors where it is heated by the sun. The heated water is then stored in a tank, sent to a tankless water heater, or used directly. These systems are preferable in climates where it rarely freezes. Freeze protection is necessary in cold climates.
Closed-loop, or indirect, systems use a non-freezing liquid to transfer heat from the sun to water in a storage tank. The sun's thermal energy heats the fluid in the solar collectors. Then, this fluid passes through a heat exchanger in the storage tank, transferring the heat to the water. The non-freezing fluid then cycles back to the collectors. These systems make sense in freezing climates.
Active, or forced-circulation, systems use electric pumps, valves and controllers to move water from the collectors to the storage tank. These are common in the U.S.
Passive systems require no pumps. Natural convection moves water from the collectors to the storage tank as it heats up.

Source: Energy Star: How It works- Solar Water Heaters

How a Solar Water Heater Works

Comparing active and passive hot water heaters (8:05)

Comparing active and passive hot water heaters

Transcript: Comparing active and passive hot water heaters (8:05)

In this video, we'll explain the inner workings of both Active and Passive Solar Water Heaters, examining their advantages, disadvantages, and real-world applications.

Active Solar Water Heaters are a marvel of engineering that relies on fluid circulation, advanced controls, and the tireless power of pumps to efficiently warm water for diverse applications in commercial and residential buildings. On the flip side, the Passive Solar Water Heater takes a more elegant, simplified approach, using nature's thermosyphon principle to create a self-sustaining flow of warm water.

Solar water heaters are described by the type of solar collector and circulation system that they use.

Active Solar Water Heaters

Active solar water heaters come in two main types: direct circulation systems and indirect circulation systems. These systems harness solar energy to heat water for various applications, such as domestic hot water, space heating, or industrial processes. Let's delve into the specifics of each type:

Direct Circulation Systems

Direct circulation systems, also known as open-loop systems, involve the direct transfer of water from the collector to the end-use application without an intermediate heat transfer fluid. This simplicity makes them suitable for regions with mild climates where freezing is not a concern.

Indirect Circulation Systems

Indirect circulation systems, also known as closed-loop systems, use an intermediate heat transfer fluid to transfer thermal energy from the solar collectors to the water in the storage tank. This allows them to operate in colder climates without the risk of freezing.

Passive Solar Water Heater

A Passive Solar Water Heater operates without the need for mechanical pumps or electrical components. These systems are less expensive than Active systems but are usually not as efficient. Without the need for moving parts, these systems can be more reliable and last longer.

Thermosyphon Systems

Like an active system, a passive system relies on a solar collector to absorb sunlight. This collector is often a dark-colored, heat-absorbing material like metal or special coatings on a surface. In a passive system, the sunlight heats the water directly without the use of a separate fluid. The collector absorbs the solar energy, and this heat is transferred directly to the water circulating through or stored in the system.

Thermosyphon Principle

The core principle behind passive solar water heaters is thermosiphon. As water absorbs heat, it becomes lighter and rises. Simultaneously, colder, denser water descends to replace it. This creates a natural circulation of water through the system.

The heated water typically rises from the collector to a storage tank located at a higher elevation. This tank is positioned above the collector to facilitate the thermosiphon effect. The warm water is stored in this tank until it is needed.

When hot water is required, it is drawn from the storage tank. The cold water that enters the collector to replace it completes the natural circulation loop, creating a continuous flow of warm water if there is sunlight.

Passive solar water heaters are characterized by their simplicity and reliance on natural processes. They are often used in residential and small-scale applications, providing a cost-effective and energy-efficient way to obtain hot water. While they may not be as suitable for large-scale commercial projects, the principles of passive solar design can still be applied to aspects of building construction to enhance energy efficiency and reduce reliance on traditional heating systems.

Storage Tanks and Solar Collectors

Most solar water heaters require a properly insulated storage tank. These tanks typically feature an extra outlet and inlet that are linked to the collector. In two-tank configurations, the solar water heater heats the water in advance of it entering the standard water heater. Conversely, in one-tank setups, the backup heater is integrated with the solar storage within a single tank.

Collector Types

Solar water heaters for residential properties usually use three different types of collectors to capture sunlight and convert it into heat for heating water. These collectors are critical components that determine the efficiency and performance of the system. Here are the main types of collectors used in solar water heaters:

Flat-Plate Collectors

Flat-plate collectors are the most common type and consist of a flat, insulated box with a transparent cover, usually glass, on top. Inside the box is a dark absorber plate, typically made of metal or other materials with high thermal conductivity. Sunlight passes through the transparent cover and strikes the absorber plate, which absorbs the solar energy and converts it into heat. The heat is then transferred to a fluid, usually water or a heat transfer fluid, flowing through tubes attached to the absorber plate.

Flat-plate collectors are versatile and used in both residential and commercial solar water heating systems. They are suitable for moderate climates and are effective for domestic hot water applications.

Evacuated Tube Collectors

Evacuated tube collectors consist of rows of glass tubes with an outer and inner tube. The air is evacuated from the space between the tubes to create a vacuum, reducing heat loss through conduction and convection. Like flat-plate collectors, sunlight passes through the outer glass tube and strikes an absorber within the inner tube. The absorber transfers the heat to a fluid circulating within the tube.

Evacuated tube collectors are more efficient than flat-plate collectors, especially in colder climates. The vacuum insulation minimizes heat loss, allowing them to capture solar energy even on cloudy days.

Evacuated tube collectors are commonly used in colder climates and are suitable for both residential and commercial applications.

Integral Collector Storage (ICS) Systems (Passive System)

ICS systems, also known as batch or breadbox collectors, integrate the solar collector and the storage tank into one unit. The collector is a black tank with a transparent cover, or dark tubes in an insulated tank. Water is heated directly in the collector, eliminating the need for separate pipes or heat exchangers. The heated water is stored in the same unit until it is used.

ICS systems are simple and cost-effective, often used in residential settings for domestic hot water applications. There should be a tempering valve that allows cold water to be mixed with the hot water coming from the tank.

They are used in open loop systems and aren’t suitable for cold climates.

The choice of collector depends on factors such as climate, available space, and the specific requirements of the solar water heating system. Each type of collector has its advantages and disadvantages, and the selection is often tailored to meet the needs of the project.

Credit: Solar Water Heaters. MEP Academy. YouTube. Accessed June 5, 2026

By reducing the amount of heat that must be provided by conventional water heating, solar water-heating systems directly substitute renewable energy for conventional energy, reducing the use of electricity or fossil fuels by as much as 80%.

Today's solar water-heating systems are proven reliable when correctly matched to climate and load. The current market consists of a relatively small number of manufacturers and installers that provide reliable equipment and quality system design.

A quality assurance and performance-rating program for solar water-heating systems, instituted by a voluntary association of the solar industry and various consumer groups, makes it easier to select reliable equipment with confidence.

Building owners should investigate installing solar hot water-heating systems to reduce energy use. However, before sizing a solar system, water-use reduction strategies should be put into practice.

Advantages and Disadvantages of Solar Hot Water Heaters

Advantages and Disadvantages of Solar Hot Water Heaters
Advantages	Disadvantages
Fuel Source is Free Passive Solar systems are great for warm climates and is a relatively simple system.	Solar hot water heating may not be suitable for every climate. Warmer climates are better suited for SHW. Indirect hot water heating will require using a heat transfer fluid, typically anti-freeze. May need additional back up system for times when weather is bad or additional hot water is needed. High upfront cost.

mxw142 Fri, 03/06/2026 - 12:39

7.7 Heat Pump Water Heaters

Heat pumps are a well-established technology for space heating. The same principle of transferring heat is at work in heat pump water heaters (HPWHs) except that they extract heat from air (indoor, exhaust, or outdoor air) and deliver it to water. Some models come as a complete package, including tank and back-up resistance heating elements, while others work as an adjunct to a conventional water heater.

The simplest HPWH is the ambient air-source unit, which removes heat from surrounding air, providing the additional benefit of space cooling. Exhaust air units extract heat from a continuously exhausted air stream and work better in heating-dominated climates because they do not cool ambient air. Some units can even be converted between the two modes of operation for optimum operation in either summer or winter.

In mild climates, you can place ambient air-source units in unheated but protected spaces such as garages, essentially using outdoor air as a heat source.

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Because it extracts heat from air, the HPWH delivers about twice the heat for the same electricity cost as a conventional electric resistance water heater.

Parts of a Heat Pump Water Heater (HPWH)

Heat Pump Water Heater Parts

Desuperheaters

The Desuperheater feature is available on some central air conditioners and is a variation of the stand-alone HPWH. It provides economical supplemental water heating as a byproduct of air conditioning.

Desuperheater water heating can be part of an integrated package with a heat pump or air conditioner system. In most such systems, the heat pump water heating only occurs during normal demand for space conditioning, with resistance electric coils providing water heating the rest of the time.

During the cooling season, the Desuperheater actually improves the efficiency of the air conditioning system while heating water at no direct cost. In an average climate, a desuperheater might meet 20 to 40 percent of annual water heating demand.

Heat pump water heaters can provide up to 60 percent energy savings over conventional water heaters.

How a Heat Pump Water Heater Works

The Heat Pump Water Heater (HPWH) consists of three circuits. The HPWH consists of three circuits. Watch the video below to learn more about how a HPWH works. (29 seconds)

How a Heat Pump Water Heater Works (0:29)

How a Heat Pump Water Heater Works

Transcript: How a Heat Pump Water Heater Works (0:29)

How a Heat Pump Water Heater Works

The heat pump water heater (HPWH) consists of three circuits; a Heat Pump circuit, a Geothermal Heat circuit, and a Desuperheater circuit.

The Heat Pump circuit consists of an indoor coil, a compressor, and a Desuperheater. Cool water flows from the indoor coil to the compressor. The water becomes heated as it travels through the compressor to the Desuperheater. The heat from the water is transferred to the water in the Desuperheater circuit through the adjacent coils.

The cool water then flows to the coils adjacent to the Geothermal Heat circuit and becomes heated as it flows back to the indoor coil.

The Geothermal heat circuit consists of a geothermal unit in the ground, a "from earth connection," and a "to earth connection." Water warmed by the earth flows from the "from earth connection" through the coils adjacent to the Heat Pump circuit, transferring the heat energy. The cool water flows back into the geothermal unit in the ground.

The Desuperheater circuit consists of the hot water tank that supplies water to the house and a set of coils adjacent to the Desuperheater coils in the Heat Pump circuit. The water from the tank cycles through the coils and is heated by the Heat Pump circuit.

Note: The concept shown in the animation is applicable to all HPWH: heat is picked up and delivered into some source – which could either be the ground, air, or water.

Most of the heat delivered to the water comes from the evaporator of the unit, not through the electrical input to the machine. Consequently, the efficiency of the HPWH is much higher than for direct-fired gas or electric storage water heaters.

The installed cost of commercial HPWH systems is typically several times that of gas or electric water heaters; yet the low operating costs can often offset the higher total installed cost, making the HPWH the economic choice for water heating.

The HPWH becomes increasingly attractive in building applications where energy costs are high, and where there is a steady demand for hot water. This attractiveness is less a function of building type than it is of water demand and utility cost.

Advantages and Disadvantages of Heat Pump Hot Water Heaters

Advantages and Disadvantages of Heat Pump Hot Water Heaters
Advantages	Disadvantages
Heat pump hot water heaters are more expensive than traditional electric hot water heaters, however they are 3-4 times more efficient than comparable electric hot water heaters.	HPHW need to be stored in a location with good airflow at least 1,000 cubic feet of air space. They should not be located in cold spaces, like a basement or garage. They are more efficient in a conditioned space with temperatures between 40-90^o F. HPHW last about 15 years, slightly longer than traditional tank hot water heaters, but not as long as on demand.

mxw142 Fri, 03/06/2026 - 12:40

7.9 Energy Efficiency

The federal efficiency standards for water heaters took effect in 1990, assuring consumers that all new water heaters meet certain minimum-efficiency levels. The latest standards went into effect in 2010, and even more strict standards will go into effect in 2029.

Water heater efficiency is reported in terms of the universal energy factor (UEF). UEF is an efficiency ratio of the energy supplied in heated water divided by the energy input to the water heater, and it is based on recovery efficiency, standby losses, and cycling losses. The higher the UEF, the more efficient the water heater.

Electric resistance water heaters have EFs ranging from 0.93 and 0.95. T
Gas water heaters from 0.63 and 0.8 with some high-efficiency models ranging around 0.93. To meet Energy Star requirements must be greater than 0.81.
Tankless gas water heaters 0.82-0.97. To meet Energy Star requirements must be greater than 0.95.
Heat-pump water heaters from 3.3-4.1. To meet Energy Star requirements must be greater than 3.30.
Solar Hot water heaters To meet Energy Star requirements must be greater than 3.00 with electric back up, and greater than 1.80 with gas back up.

Want more info Icon DOE replaced Energy Factor (EF), the previous measure, in 2017 with the adoption of revised testing procedures and metrics to help consumers and contractors easily and precisely compare the efficiency among water heaters for a given installation scenario. UEF provides a consistent standard, simplifies the selection process, and more accurately measures energy usage under real-world conditions compared to previous measurement models. For more information, check out Energy Star's website on "What is Uniform Energy Factor and Why Does it Matter?"

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Other Considerations

In addition to UEF, also look for a water heater with at least one-and-a-half inches of tank insulation and a heat trap. If your (tank) hot water heater is older, you can increase the efficiency by adding a hot water heater blanket. The can increase the R-value (insulation) of the hot water heater by trapping the heat inside. They can be purchased at any home improvement store for about $20-$40.

In addition, capacity of a water heater is an important consideration. The water heater should provide enough hot water at the busiest time of the day. For example, a household of two adults may never use more than 30 gallons of hot water in an hour, but a family of six may use as much as 70 gallons in an hour.

The ability of a water heater to meet peak demands for hot water is indicated by its "first hour rating." This rating accounts for the effects of tank size and the speed by which cold water is heated. Water heaters must be sized properly. Over-sized water heaters not only cost more but increase energy use due to excessive cycling and higher standby losses.

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7.10 Comparing Hot Water Heaters

Let’s use the Energy Guide to perform a life-cycle analysis to help choose a water heater. Different models of water heaters with roughly the same capacity can vary dramatically in the amount of energy they use.

Instructions: Look at the Energy Guides for these three different water heaters and answer the questions below.

The prices of the water heaters are not included on the Energy Guide labels, so I've listed them for you.

Electric Water Heater (Tank) $549
Natural Gas Water Heater (Tank) $689
On Demand Electric Water Heater $459

Energy guide label for three different water heaters. Each label is described in detail below. — Energy Guide Labels

Quiz Yourself

After looking through the information on the three Energy Guide labels, see if you can answer the following questions.

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Still trying to figure out the payback period between the two tank heaters? The price difference between the two models was $140, with the electric water heater being cheaper to buy, and your annual savings for operating the water heater were $164, with the gas water heater being cheaper to operate. So after one year, you got back $164 out of the $140 extra you spent on the superior model. It took you less than a year to pay back the extra money you spent on the more expensive model.

Obviously, over time, it pays to buy an energy-efficient water heater. It also helps the environment by not using as much energy and thereby not emitting as much CO₂, NO_x, SO_2,CO and particulate matter into the environment.

mxw142 Fri, 03/06/2026 - 12:42

7.11 Heating Hot Tubs and Pools

Heating pools and hot tubs require a lot of energy use because we are heating A LOT of water. As we learned earlier in the lesson the amount of energy required to heat water depends on the amount of water and pools an hot tubs use a significantly larger volume of water compared to residential hot water use.

Pool water temperatures typically range from 78-82°F. The volume of water in a pool can vary significantly compared to the size, style and depth of the pool. The manufacturer will likely tell you the amount of water your pool can hold, but you can estimate it based upon online calculators or simple geometry.

Example - Heating a Pool

A round above ground pool that is 4 feet in depth. We can estimate the volume of water required by getting the radius (or diameter) of the pool. If the radius of the pool is 6 feet (diameter is 12 feet) the volume of the water is ${Volume = Pi×Radius}^{2} ×depth$ .

${Volume = Pi×(6 ft)}^{2} ×(4 ft)$

${Volume = 3.14×(6 ft)}^{2} ×(4 ft)$

${Volume = 452.16 ft}^{3}$ so we need to convert that to gallons, knowing that ${1 ft}^{3} = 7.48 gallons$ .

${Volume = 452.16 ft}^{3} \times (7.48 gallons / {1 ft}^{3}) = 3,382 gallons$

So this pool would require about 3,382 gallons of water!

As you can see, this is a relatively small pool, but uses a significant amount of water.

The calculations get more complicated if you have a different shaped pool or have a deep end. However, there are lots of online calculators that will help you estimate the gallons of water needed.

Hot Tubs are another high hot water demand device that may be found in some homes. Hot tubs are typically operated at higher temperatures between 100-104°F. Most of the energy use is to heat the water, over 75%. The remaining energy use can be from the pumps, jets and lighting. In colder climate conditions the energy use may be higher to get that temperature up.

Example - Heating a Hot Tub in Maine vs. Florida

Calculate the energy used to heat water for a 500 gallon hot tub in Maine versus Florida. In Maine the outdoor temperature is 25°F while in Florida is 65°F. Assume the operation temperature of the hot tub is 102°F.

Calculate the amount of energy required in each location.

Recall our Water Heating formula is:

$Q = m \times C_{p} \times ∆ T$

We also know:

$C_{p} = 1 B T U / (l b \times ° F)$

and

$1 gallon of water = 8.34 pounds$

Energy Calculations
Maine	Florida
$m =500 gal× (8.34 lbs / gal) = 4,150 lbs$	$m =500 gal× (8.34 lbs / gal) = 4,150 lbs$
$C_{p} = 1 BTU / lb \times ° F$	$C_{p} = 1 BTU / lb \times ° F$
$Δ T = 102 ° F - 25 ° F = 77° F$	$Δ T = 102 ° F - 65 ° F = 37° F$
$Q_{Maine} = 4,150 lbs× (1 BTU / (lb \times °F)) \times 77° F$	$Q_{Florida} = 4,150 lbs× (1 BTU / (lb \times °F)) \times 37° F$
$Q_{Maine} = 319,550 BTUs$	$Q_{Florida} = 153,550 BTUs$

A hot tub in Maine uses more than double the amount of energy than one in Florida in order to heat the water!

Type of Water heaters for pools and hot tubs

Just like we saw with residential hot water heaters, pools and hot tubs can be heated in a variety of ways including electric, natural gas, solar and heat pump.

Heat Pump Hot Water Heaters

Just like we saw with residential hot water heaters, heat pumps have higher efficiency because they use some of the energy available in surrounding air to help heat the water. Heat pump will work more efficiently in temperatures above 50°F.

Diagram of a heat pump system for pool heating with components labeled 1 to 10. — Heat Pump Hot Water Heater for Pools

Just like we saw with other types of water heating, the heat pump hot water heater is more expensive, but has less operating costs. Heat pump efficiencies range from 3.0-7.0, which means they get more energy out per unit of electricity put in. This isn’t magic, heat pumps just pull some energy out of the ambient air.

Solar Swimming Pool Heaters

Solar Swimming Pool Heaters use a solar collector to convert energy from the sun to heat the pool water. They tend to have the lowest operating cost and can be the most cost-effective solution in some climates.

Most solar pool heating systems include the following:

A solar collector — the device through which pool water is circulated to be heated by the sun
A filter — removes debris before water is pumped through the collector
A pump — circulates water through the filter and collector and back to the pool
A flow control valve — automatic or manual device that diverts pool water through the solar collector.

Pool water is pumped through the filter and then through the solar collector(s), where it is heated before it is returned to the pool. In hot climates, the collector(s) can also be used to cool the pool during peak summer months by circulating the water through the collector(s) at night.

Diagram of a solar pool heating system with pool equipment, solar collectors on a roof, and a conventional pool heater. — Diagram of a solar pool heating system

How to reduce your energy use in your pool or hot tub:

Use a high quality cover to keep as much heat inside. A lot of heat is lost from the top of the pool or hot tub, so keep it covered and insulated as much as possible when not in use. A cover will also reduce evaporation.
Lowering the temperature just a few degrees can reduce your energy costs
Maintaining a constant temperature is more efficient than increasing and decreasing the temperature constantly.
Off peak heating, using a timer to heat during off peak (cheaper) times
Keep filters clean and free of debris

mxw142 Fri, 03/06/2026 - 12:43

7.12 Water Heaters: Energy Saving Tips

Do as much cleaning as possible with cold water to save the energy used to heat water.
Check your faucets for leaks. They waste both water and energy!
Conserve hot water by installing water-saving showerheads.
Once your water is hot, insulate to help keep it that way. Wrapping exposed hot water pipes with insulation will minimize heat loss. So will installing an insulation blanket around your water heater.
Reduce your water heater's temperature to 120 degrees Fahrenheit. That will produce plenty of hot water and still save energy. For homes with a dishwasher, a setting of 140 degrees is required to clean properly, but most of the new dishwashers have a built-in water temperature booster.
Replace old hot water heaters with more efficient technologies like heat pump or on demand hot water heaters.
Many new water heaters have a "vacation" setting you can use to save energy if you're away for more than a few days. Turn the thermostat "down" or "off" when you're gone for more than three days.
If you have a pool or hot tub, make sure you keep it covered with a well-insulated cover when not in use to keep heat inside.

mxw142 Fri, 03/06/2026 - 12:44

7.13 Review

In this lesson, we explored the many ways homes heat water and why those choices matter. From traditional hot water tanks to high‑efficiency heat pump systems, you saw how different technologies balance cost, convenience, and energy use. We also looked at how solar hot water systems can tap into renewable energy, and how pools and hot tubs—often overlooked—can become major energy users if they aren’t heated wisely.

The big takeaway is that hot water isn’t just something that “shows up” when you turn on the tap. Every gallon requires energy, and the systems we choose have real impacts on our utility bills and the environment. As you continue learning about energy use in the home, keep thinking about how everyday technologies—like water heaters—shape both our comfort and our energy footprint. Understanding these systems is the first step toward making smarter, more sustainable choices.

mxw142 Fri, 03/06/2026 - 12:45

Lesson 7: Hot Water

7.1 Lesson 7 Introduction

Welcome to Lesson 7

Lesson Objectives

7.2 Water Heaters

Types of Water Heaters

Costs of Water Heaters

Typical Water Use at Home

7.3 Energy Required for Water Heating

Example 1

Example 2

7.4 Storage Tank Hot Water Heaters

Parts of an Electric Hot Water Heater

Parts of a Gas Hot Water Heater

How a Gas Hot Water Heater Works

How Do Gas Hot Water Heaters Work? (8:18)

Advantages and Disadvantages of Tank Water Heaters

To Learn More

How to Maintain an Electric Water Heater (4:46)

7.5 Demand Water Heaters

How a Demand Water Heater works

How Tankless Water Heaters Work (1:08)

Advantages and Disadvantages of Demand Water Heaters

7.6 Solar Water Heaters

Collector Types

Circulation Systems

How a Solar Water Heater Works

Comparing active and passive hot water heaters (8:05)

Advantages and Disadvantages of Solar Hot Water Heaters

7.7 Heat Pump Water Heaters

Parts of a Heat Pump Water Heater (HPWH)

Desuperheaters

How a Heat Pump Water Heater Works

How a Heat Pump Water Heater Works (0:29)

Advantages and Disadvantages of Heat Pump Hot Water Heaters

7.9 Energy Efficiency

Other Considerations

7.10 Comparing Hot Water Heaters

Quiz Yourself

7.11 Heating Hot Tubs and Pools

Example - Heating a Pool

Example - Heating a Hot Tub in Maine vs. Florida

Type of Water heaters for pools and hot tubs

Heat Pump Hot Water Heaters

Solar Swimming Pool Heaters

Example - Heating a Freshly Filled Hot Tub

Test Your Knowledge

7.12 Water Heaters: Energy Saving Tips

7.13 Review