Conventional gas water heaters present an additional challenge to the home owner improving the energy efficiency of their water heater. In addition to the energy loss through demand, standby and distribution (as previously discussed), the conventional gas water heater will waste a greater percentage of energy than electrical water heaters due to the design of the burner and ventilation system.
The wasted energy specific to gas and oil water heaters are: excess air, dilution air and off-cycle air circulation.
Approximately 15 cubic feet of air is required to efficiently burn one cubic foot of gas. Wasted heat and combustion by-products are carried by air through the chimney and are not heating water. Some of this waste cannot be avoided, but the more excess air that flows through the burner the more energy is wasted.
Dilution air is air from within the room that enters the flue at the draft diverter during combustion to assist in providing the draft needed to carry the dangerous combustion by-products to the outdoors. Some or all of this dilution air is air that has been heated or cooled from the home.
Off-Cycle Air Circulation
Surrounding indoor air circulates through the burner and flue, carrying the heat away from the water (and conditioned air away from the home) and up the chimney.
There are improved gas and oil water heaters that reduce these losses that are directly related to ventilation by restricting the air that flows through the flue and chimney. Some designes have eliminated the draft diverter.
By restricting the air flow through the flue and chimney, air circulation carrying the heat away from the tank has been reduced.
None of these are modifications that the home owner should do on their own since proper drafting through the flue and chimney are necessary to ensure that the dangerous by-products and gases produced during the combustion process are safely vented to the outdoors.
Since gas is a less expensive energy resource than electricity, many home owners will want to find the way to efficiently use it as opposed to replacing their gas appliances with those using more costly electricity. The professional who conducts the diagnostic home performance evaluation will assist the home owner in locating a qualified contractor who can safely affect these changes.