Storage Water Heaters
The storage water heater is by far the most common type of water heater in use today. They range in size from 20 to 75 gallons (or larger) and are fueled by natural gas, propane, electricity, or oil. Because heat is lost through the flue (except in electric models) and through the walls of the storage tank, energy is consumed even when no hot water is being used.
New energy efficient gas fired storage water heaters are a good cost effective replacement option if there is an existing gas line in the home. With more insulation around the tank and one-way valves where pipes connect to the tank, standby heat loss is substantially reduced. Prices are dropping for promising new super-efficient "condensing" and "near-condensing" gas water heaters which save energy over traditional models. A condensing gas water heater works like a normal tank-type water heater, except that before the combustion gases are vented outside, the heat in those gases is captured and used to help heat the water in the tank.
In general, most choices available for natural gas are also sold for propane. For safety as well as energy efficiency, fuel-burning water heaters should be installed with sealed combustion ("direct-vented" or "power-vented"). Sealed combustion means that outside air is brought in directly to the water heater and exhaust gases are vented directly outside, keeping combustion totally separate from the house air.
If there is no access to natural gas or propane, rather than choosing an electric storage water heater a homeowner may want to consider a heat pump water heater, which is more efficient, but also more expensive. Conventional electric storage gas water heaters will still comply with Title 24 standards when using the performace calculation method.