Types of residential water heaters

Other differences can include leak detection, and the 'energy save module' on some models that lets user select heating mode, such as energy-saver or standard, etc
The heater also has grid capability and can be enrolled in a demand response program that cuts power to appliances when demand on the grid exceeds capacity.
The same design heater is offered in 80 gallon size demand-response model, seen below #5.

Electric heaters make up about 39% of residential market while Gas heaters are about 59% of market with solar, wood burning, oil and other types of heaters making up the balance. Residential Electric heaters are powered by 120 or 240 volt, and require no flue pipe. Residential Gas water heaters burn either propane or natural gas and require a flue or vent pipe to vent toxic combustion by-product. Gas heaters are powered by a thermocouple, thermopile, or by 120 or 24VAC, depending on type of heater and gas valve. Both gas and electric heaters come in several sizes, dimensions and varieties. Selection of heater depends on available energy source, gallons of hot water needed and regulations. Regulations include April 2015 DOE standard for higher efficiency that require higher technology for larger heaters over 55 gallon. Some State, regional and local governments have mandates for low NOx and ultra low NOx burners on heaters with less than 100,000 BTU. All heaters with 100,000 BTU burner or more must have ultra low NOx burner. Electric heaters have higher efficiency since the elements are immersed completely in water. Gas heaters have lower efficiency since much of the combustion heat is lost up the flue pipe. Despite lower efficiency, gas heaters are cheaper to operate and generally heat more water per hour than electric heaters because burning gas releases more BTU energy than 240 volt electric element can produce. Residential heaters typically have 1"-2" non-CFC foam insulation. Most residential tanks are made from steel and are rated for 300psi, with maximum working pressure of 150psi. There is one brand with a non-metallic polybutylene tank that is likewise rated max working pressure of 150psi, but otherwise steel is universally used for water heater tanks. All gas and electric water heaters must have a TP valve that can release water if temperatures exceed 210°F or pressures exceed 150psi. The TP valve must have a rating that shows it can release more BTU energy than the heater can produce. TP Valve code Maximum temperature for any water heater, residential or commercial, gas or electric, is 210° to prevent steam explosion.
Types of Electric heaters
	1. Ordinary electric water heater/ 30-40-50-55 gallon Electric heaters 30-55 gallon are generally same design as each other, usually with 2 heating elements. All 2-element tanks are 240 volt. How electric water heaters work The thermostats on this heater are mechanical bi-metal switches that read water temperatures by sitting flat against the steel tank. Elements and other parts are generic and widely available for simple do-it-yourself repairs. The anode rod is necessary on steel tanks to prevent tank from rusting. Inspection of anode and general upkeep maintenance will result in almost indefinite life of these water heaters. This type electric heater can be connected to 120 volt, can be connected to 120 volt generator, and can be wired many ways to meet different objectives. Resources: Troubleshoot electric water heater How to maintain water heater How to wire water heater thermostats Convert water heater to 120 volt Connect water heater to generator Convert water heater to low voltage solar Convert to high volt solar Specification sheet
Larger image	2. Mobile Home Electric/ 30-40 gallon These heaters are same as ordinary 2-element 240 volt water heater #1 shown above. The only difference is mobile home heaters have side connections for water instead of top connections. All electric water heaters (ordinary top connected or side connected) are certified for manufactured housing.
Larger image	3. Energy Smart electronic water heater/ 40-50-55 gallon Formerly called energy smart, now called 'heaters with electronic thermostat,' or 'electronic display.' These heaters are generally same as ordinary 2-element 240 volt water heaters shown above. The main operational difference is they have electronic upper thermostat and a thermistor (heat sensitive resistor) located in lower part of tank instead of generic upper and lower mechanical thermostats. Other differences can include leak detection, and the 'energy save module' on some models that lets user select heating mode, such as energy-saver or standard, etc The heater also has grid capability and can be enrolled in a demand response program that cuts power to appliances when demand on the grid exceeds capacity. The same design heater is offered in 80 gallon size demand-response model, seen below #5. Promotional literature says the 'Electronic thermostat gives faster response to water temperatures," which might mean more accurate range of calibration. Otherwise the electronic parts add no value for customer unless the display model is installed and set to more efficient mode. Even so, any gain is questionable since it takes same KWh of energy to heat water no matter which mode is set, and if the purpose is to avoid peak pricing, a simple timer is more versitile. Resource: Boxtype The non-generic electronic thermostat and thermistor can be ordered from water heater manufacturer when they fail. Ordinary electric heaters #1 and #2 use generic mechanical thermostats from hardware store. The energy smart series heaters can be converted into regular heater. Resources: Review Energy Smart Convert Energy Smart into regular heater Spec sheet with electronic thermostat Energy Smart spec sheet 2020 Energy Smart manual 2020
	4. Under counter/ Point of use heaters/ 5-10-20 gallon Small one-element heaters can provide 'instant' hot water at a sink. The 20 gallon size can provide enough hot for quick shower. Typical shower is 104° and consumes 9 gallons hot water.. Small heaters can also assist main water heater. Resource: How to install point of use water heater
Larger image	5. Dual-element 80 gallon grid enabled or demand response water heaters/ Since the April 2015 energy standard, you can no longer buy a dual-element 80 gallon electric heater of any brand without enrollment into a demand response program where grid can disable lower element when needed. 80 gallon grid enabled/ demand response spec sheet Marathon demand response spec sheet
	6. Heat pump electric water heaters/ If home has 5-7 people, and needs tank that is larger than 55 gallon electric water heater ... or home needs more hot water for walk-in bathtub or high usage, then a heat pump (hybrid) heater is mandated by the April 2015 DOE energy standard. Or home can install two 40-50 gallon heaters. Heat pumps are expensive to buy and require regular maintenance, but have higher efficiency than typical tank type electric water heater. Heat pumps are large, heavy and generally not DIY repair. The 80 gallon heat pump can deliver just 80 gallon of hot water and less in cold winter months. 80 gallon heat pump takes 4-6 hours or longer to reheat full tank. While government and manufacturer resources show amazing savings from a heat pump vs ordinary electric heater, real-world numbers are not available to prove the 'savings' vs cost of purchase, installation, maintenance, repair, limited lifespan, aggravation and replacement cost. It is probably the case that Heat pumps can save money in some installations. Because heat pumps draw heat for the water from the furnace, while cooling the room, they are best suited to warm climates ... in colder regions it might be cheaper overall to buy and operate 2 ordinary electric water heaters instead of using furnace to heat water. Resources: Which is best heat pump hybrid Review GE heat pump Two-water-heaters

Gas Water Heaters/ about 58% of market
Larger image	1. Ordinary Atmospheric vented water heaters/ 30-40-50 gallon Atmospheric vented water heaters have a pilot flame, and a thermopile or thermocouple depending on gas control valve. Resources: Troubleshoot gas water heater Basic parts for gas water heater
	2. Atmospheric vent mobile home/ 30-40 gallon Same as ordinary residential heater except smaller 35,000 BTU burner, lower efficiency, 30-40 gallon size for less width, and side connections for water. Otherwise, the mobile home atmospheric installs and functions same as ordinary atmospheric heater shown above. Resources: Manual Mobile home spec sheet
Larger image	3. Direct vented water heaters/ 40-50 gallon Direct vented heater functions same as ordinary atmospheric heater #1 shown above, except the vent and air intake are designed differently. All direct vent type water heaters draw some or all air supply needed for combustion from outside the home. All direct vented water heater have a dual vent ... with a 3" vent pipe inside 6" inlet pipe. The heater draws 'make-up air' from outside home through the 6" inlet pipe and then vents air out through the 3" vent pipe. Make up air would be the air that is pulled in from outside to replace the air needed for complete combustion of fuel. As the gas water heater burns fuel, it draws air into the heater via the 6'' tube and exhausts air out through the 3'' vent. There are two general types of direct vent. The mobile home type that vents up through the roof, and the household type that vents through sidewall of home, or through the roof. Both have dual vent system. These heaters have a pilot flame, and a thermopile or thermocouple depending on gas control valve. Resources: Direct-vent-manual Direct vent manual 2020 AO Smith direct vent spec sheet Install direct vent
Larger image	4. Direct vent mobile home/ 30-40-50 gallon Direct vented heater functions same as mobile home atmospheric heater #2 shown above, except the vent and air intake are designed differently. All direct vent type water heaters draw some or all air supply for combustion from outside the home. Side connections for hot and cold water Mechanical gas valve is factory default for natural gas ... but can be converted to propane. Call propane company for conversion. Are 18"-20-22" wide for small footprint, with 30,000 BTU burner instead of 40,000 BTU found on residential heaters Resources: Mobile-home-direct-vent-manual Mobile-home-direct-vent-spec sheet 30-40-50 gallon
Larger image	5. Flue dampered water heaters/ 30-40-50 gallon Flue dampered heaters plug into 120 volt outlet. The gas valve is powered by 120 volt or 24 volt AC depending on manufacturer. The gas valve circuit board controls all operations. Flue damper heaters have a motorized damper located on top of heater that opens and closes at top of flueway. The purpose of the damper is to slow the exit of heat when water heater is in standby mode. This increases standby efficiency. These heaters have a pilot flame, that activates when gas is released to burner. The pilot flame goes out after the heat cycle. Not having a continual, or standingpilot flame also increases overall efficiency. Resources: Flue damper manual Flue damper spec sheet Flue damper spec sheet2 Review AO Smith flue damper Review Whirlpool flue damper heater
Larger image ultra low NOx power vent	6. Power vent water heaters/ 40-50-75 gallon Power vented heaters have 120 blower motor located on top of heater. A single 2" or 3" approved vent pipe attaches to the blower. The blower draws air into the combustion chamber from inside the home, and then pushes the hot combustion gasses out of the house through the 2" or 3" or 4" vent pipe. The vent can terminate through a side wall or through a roof vent. The power vented heater can vent up to 180' because of the blower. Power direct vent heaters plug into 120 volt outlet. Correct polarity and reliable noise-free power are needed for correct operation of heater. On modern heaters with electronic gas valve, the gas valve and circuit board are powered by household voltage and heater does not have thermopile or thermocouple. Most modern power vented heaters have hot surface ignition and do not have a pilot light. Resources: Power vent spec sheet Power vent manual 75 gallon power vent manual Resource: How to troubleshoot power vent water heater Directory power vent manuals
Larger image ultra low NOx power vent	7. Power Direct vent water heaters/ 40-50-75 gallon All direct vent type water heaters draw some or all air supply for combustion from outside the home. Power direct vented heaters draw all air from outside. A power direct vent has a 2" or 3" or 4" pipe that connect to the blower motor located on top of heater ... and another 2" or 3" or 4" pipe that connect to the air intake. The blower draws air into the water heater through one pipe, and vents the combustion by-product out the other pipe. The intake and vent pipes can terminate through a side wall or through a roof vent. A power direct vented heater can vent up to 180' if the correct vent diameter is used. Power direct vent heaters plug into 120 volt outlet. Correct polarity and reliablesurge and noise-free electric power are needed for correct operation of heater. On modern heaters with electronic gas valve, the gas valve and circuit board are powered by household voltage and heater does not have thermopile or thermocouple. Modern power direct vented heaters have hot surface ignition and do not have a pilot light. Resources: Power direct vent spec sheet Power direct vent manual Power direct vent manual Directory power vent manuals
	8. Condensing water heaters/ Power vent and power direct vent If home has 5-7 people, and more hot water is needed, up to 135+ gallons first hour ... or home needs tank that is larger than the typical 50-55 gallon heater that delivers 80 gallon first hour ... then a condensing heater is mandated by the April 2015 DOE energy standard. Condensing heaters are expensive to buy, maintain and repair, but have 80-82% overall efficiency vs 62-63% efficiency of typical 50 gallon gas water heater. The high-tech condensing heater with electronic controls make the unit susceptible to surge and other failures typically found with electronic appliances, such as overpriced parts. It is probably still cheaper overall to buy and operate 2 ordinary gas water heaters, despite the lower efficiency. Resources: Review Polaris condensing heater Vertex condensing heater Two water heaters