Hot Water Heaters Conventional Storage Water Heaters
Conventional storage water heaters remain the most popular type of water-heating systems for the home. Here you'll find basic information about how storage water heaters work, what criteria to use when selecting the right model and some installation, maintenance, and safety tips.
How They Work A single-family, storage water heater offers a ready reservoir—from 20 to 80 gallons—of hot water. When you turn on the hot water tap, hot water is released from the top of the tank. Cold water then fills into the bottom of the tank, ensuring that the tank is always full.
Conventional storage water heater fuel sources include natural gas, propane, fuel oil, and electricity.
Natural gas and propane water heaters basically operate the same. A thermostat opens the gas valve as the water temperature falls and a gas burner under the tank heats the water. The valve closes when the temperature rises to the thermostat's set point turning off the gas.
Oil-fired water heaters operate in much the same way but they have power burners that mix oil and air in a vaporizing mist ignited by an electric spark. Electric water heaters have one or two electric elements each with their own thermostat, a standby element maintains the minimum thermostat setting while another provides hot water recovery when demand heightens.
Because water is constantly heated in the tank, energy can be wasted even when a hot water tap isn't running. This is called standby heat loss. Only tankless water heaters—such as demand water heaters and tankless coil water heaters—avoid standby heat losses. However, you can find some storage water heater models with heavily insulated tanks, which significantly reduce standby heat losses, lowering annual operating costs. Look for models with tanks that have a thermal resistance (R-Value) of R-12 to R-25.
Gas and oil water heaters also have venting-related energy losses. Two types of water heaters—a fan-assisted gas water heater and an atmospheric sealed-combustion water heater—reduce these losses. The fan-assisted gas water heater uses a draft-induced fan that regulates the air that passes through the burner, minimizing the amount of excess air during combustion, increasing efficiency. The atmospheric sealed-combustion water heater uses a combustion and venting system that is totally sealed from the house.
You might also want to consider some less conventional storage water heaters—heat pump water heaters and solar water heaters. These water heaters are usually more expensive but they typically have lower annual operating costs. Selecting A New Water Heater Whether you’re replacing a worn-out existing water heater or looking for the best model for a new house you’re building, it pays to choose carefully. Look for a heater that satisfies your needs and uses as little energy as possible. Often you can substantially reduce your hot water needs through water conservation efforts. Think About a Replacement Now If you're like most people, you’re unlikely to go out looking for a water heater until your existing one fails, leaving little time to look for a heater that most appropriately fits your needs and offers the highest level of energy efficiency. A much better approach is to do some research now. Figure out what type of water heater you want—gas or electric, storage or demand, stand-alone or integrated with your heating system, etc. and then, figure out the proper size for your household. Sizing a Water Heater The capacity of a water heater is an important consideration. The water heater should provide enough hot water at the busiest time of the day. The ability of a storage 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. Demand water heaters should be sized according to the required gallons per minute (gpm) flow rate and temperature rise required for your largest expected hot water fixture (usually a shower). Indirect water heaters offer a more efficient choice for most homes, even though they require a storage tank. An indirect water heater uses the main furnace or boiler to heat a fluid that's circulated through a heat exchanger in the storage tank. The energy stored by the water tank allows the furnace to turn off and on less often, which saves energy. An indirect water heater used with a high-efficiency boiler and well-insulated tank can be the least expensive means of providing hot water.
Indirect systems can be fired by gas, oil, propane, electric, solar energy, or a combination of any of these. Tankless systems are typically electric or gas-fired. Also, these integrated or combination water-heating systems not only work with forced air systems but also with hydronic or radiant floor heating systems. Fuel Options What type of fuel makes the most sense for your water heater?
If you currently have an electric water heater and natural gas is available in your area, a switch might save you a lot of money. Oil, Gas and propane-fired water heaters are also usually less expensive to operate than electric models in our area.
Look for Sealed Combustion or Power-Vented Systems For safety as well as energy efficiency, look for gas or oil-fired water heaters with sealed combustion or power venting. Sealed combustion means that outside air is brought in directly to the water heater and exhaust gases are vented directly outside, totally separate from the in-house air. Power-vented equipment may use house air for combustion, but flue gases are vented to the outside with the aid of a fan. In very tight houses, drawing combustion air from the house and passively venting flue gases up the chimney can sometimes result in backdrafting of dangerous combustion gases into the house.
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