Conventional storage water heaters remain the most popular type of water heating system 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. It operates by releasing hot water from the top of the tank when you turn on the hot water tap. To replace that hot water, cold water enters the bottom of the tank through the dip tube where it is heated, ensuring that the tank is always full.
Conventional storage water heater fuel sources include natural gas, propane, fuel oil, and electricity.
Since water is heated in the tank until the thermostat setpoint temperature is reached, energy can be wasted even when a hot water tap isn’t running due to standby heat losses, which result from the tank losing heat to the surrounding environment. Only tankless water heaters — such as demand-type water heaters and tankless coil water heaters — avoid standby heat losses. Some storage water heater models have heavily insulated tank, which significantly reduce standby heat losses and lower annual operating costs. Look for models with tanks that have a thermal resistance (R-Value) of R-24 and above to avoid adding an insulation blanket (electric water heaters only).
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. Visit the Energy Basics site to learn more about how conventional storage water heaters work.
For low energy bills the best choice to consider are heat pump water heaters and solar water heaters. These water heaters are usually more expensive but they have significantly lower annual operating costs that result in short payback periods.
Selecting a Storage Water Heater
The lowest-priced storage water heater may be the most expensive to operate and maintain over its lifetime. While an oversized unit may be alluring, it carries a higher purchase price and increased energy costs due to higher standby energy losses.
Before buying a new storage water heater, consider the following:
- Size and first hour rating
- Fuel type and availability
- Energy efficiency and costs.