Water Heater Types
Conventional Tank, Natural Gas
A gas burner, typically located at the bottom of the unit, heats water in the tank above. The tank stores heated water until use. Exhaust gases are vented through a vertical flue in the center of the tank. Conventional models pull make-up air for combustion directly from the house and use the natural rise of hot air to vent exhaust gases. Power vent models add an electrically powered fan to vent exhaust gases with more force, overcoming wind and house depressurization. Direct vent models improve on this system by providing makeup air directly to the burner, eliminating the need to pull make-up air from the house. This creates a sealed combustion chamber so that the unit consumes no house air and exhaust gases cannot spill into the house.
Gas Condensing Tank
Rather than venting exhaust gases straight out of the water heater, condensing units force the exhaust gases through a long helical coil. This helps extract more heat from the combustion process and cools the exhaust gases to the point of condensation. This phase change from exhaust gas to liquid adds further heat to the water in the tank. Condensed exhaust liquid is drained away as slightly acidic water and an electrically powered fan vents the remaining exhaust.
When hot water is called for, a gas burner ignites to heat water as it flows through the unit. A heat exchanger is used to transfer heat from the exhaust gases to the water loops. No hot water is stored within the unit. Larger capacity units can heat water at a higher rate, increasing hot water flow (gallons per minute) or the temperature gain of the incoming water. Cold incoming water temperatures (below 50°F) can slow the rate of hot water delivery. In general, tankless systems require some electricity for power venting and computer controls.
Conventional Tank, Electric
Electric resistance heating elements submerged in the tank heat water directly. No exhaust gases are produced at the site of the water heater. The tank stores hot water until use.
Solar Hot Water
Solar hot water heaters warm water through direct solar energy. A number of system types are readily available, including active systems, passive systems, flat panel systems, and evacuated tube collectors. Solar hot water can be used for domestic hot water or space heating with radiant systems.