Today’s high-efficiency commercial gas water heaters include on-demand tankless water heaters, indirect water heaters, and gas-condensing water heaters.
Indirect water heaters use your building’s space heating system to heat water. They're part of what's called integrated or combination water and space heating systems.
Indirect Water Heaters
An indirect water heater uses the main furnace or boiler to heat a fluid that's circulated through a heat exchanger in a 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 is used with a high-efficiency boiler and well-insulated tank can be the least expensive means of providing hot water.
Tankless Water Heaters
A tankless water heater provides hot water on demand without a tank. When a hot water faucet is turned on, water is heated as it flows through a heating coil or heat exchanger installed in a main furnace or boiler. Tankless coil water heaters are most efficient during cold months when the heating system is used regularly and can be a less-efficient choice in warmer climates.
Gas condensing water heaters
Gas condensing water heaters work much like regular gas water heaters: a large, insulated tank of water is heated by a gas burner. But instead of venting the combustion gases directly outside, those gases are captured and utilized to heat the water even more.
A standard gas storage water heater is like a water tank sitting atop of a gas fireplace with the chimney running straight up through the middle, exiting at the top. A gas condensing water heater has its "chimney" or flue designed with greater surface area. The heat and combustion gases have much farther to travel before they exit the water tank, so more heat is transferred to the water in the tank.
Condensing gas water heaters require:
- A different exhaust system with a blower since the cooler exhaust gases cannot be vented up the chimney
- A floor drain to condensate pump to remove condensate
- Connection to a 120 V electric outlet