7.4 Storage Tank Hot Water Heaters
7.4 Storage Tank Hot Water HeatersThe 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
Text description of the Electric Hot Water Heater image.
The image is a labeled diagram of a vertical cylindrical water heater with various components numbered and listed. The main body of the heater is shown in a cross-sectional view, revealing the internal parts. The outer shell is gray, with the top and bottom ends colored in blue. On top, component 1 is the cold water valve, and component 3 is the temperature and pressure relief valve. Component 2, labeled as the electric supply, is depicted with wires entering from above. Component 4 is the overflow pipe extending to the side. A vertical yellow pipe inside the cylinder represents component 5, the anti-corrosion anode. Another vertical pipe, component 6, labeled as the dip tube, runs alongside it. Two red rectangular zones within the heater represent the upper and lower heating elements, components 7 and 8, respectively. Component 9, the drain valve, is located near the bottom right side of the heater. Components 10 and 11, the upper and lower thermostats, are indicated on the side next to the heating elements.
Transcribed Text:
- Cold Water Valve
- Electric Supply
- Temperature and pressure relief valve
- Overflow pipe
- Anti-corrosion anode
- Dip tube
- Upper Element
- Lower Element
- Drain valve
- Upper thermostat
- Lower thermostat
Parts of a Gas Hot Water Heater
Text description of the Gas Hot Water Heater image.
The image is a labeled diagram of a water heater, illustrating various parts and their functions. The heater is depicted in a vertical cutaway view, showing interior and exterior components. At the top, an outlet to the chimney is connected to a flue, allowing exhaust gases to escape. A cold water valve is situated at the top left, feeding into the dip tube which runs vertically along the side. Below the flue is a draft-diverter. The body of the heater contains a temperature and pressure relief valve and an overflow pipe, positioned on the left. Inside, an anti-corrosion anode runs along the vertical length. On the right, externally mounted, is an on/off pilot, shutoff valve, temperature control, and gas supply line leading to the burner at the base. A drain valve is also placed towards the bottom right. The thermocouple and air shutter are positioned near the burner to regulate gas flow and ensure safe operation.
Transcribed Text:
- Outlet to chimney
- Flue
- Cold water valve
- Draft-diverter
- Temperature and pressure relief valve
- Overflow pipe
- Anti-Corrosion anode
- Dip tube
- On/Off pilot
- Shutoff valve
- Temperature control
- Gas supply
- Drain valve
- Thermocouple
- Burner
- Air shutter
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)
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.
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
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