The phrase “hot water heaters” used to mean big tanks with fires underneath powered by oil or gas. Now, hot water heaters may be gas- or electric-powered, may make use of new technologies, and are so varied in design and implementation that the homeowner often finds himself overwhelmed with options galore. In this blog article, I will try to put these numerous options into perspective.
The traditional tank hot water heaters are still what I as a home inspector most commonly see. But with the trend towards green buildings and energy conservation, I expect to see high efficiency implementations more often. These might be stand-alone hot water heaters with elongated heat exchangers and/or direct venting, or they might use heat pump technology (either wholly separate or in conjunction with a conventional tank). High-efficiency hot water heaters introduce new requirements, such as the need to drain condensate, but the savings is usually worth it.
Evolution of General Heating Concepts
Heat began with fire, which requires a reasonable mix of both fuel and combustion air to burn. Heating a space or room with fire is relatively inefficient, plus the exhaust fumes and other byproducts need to be vented away from the space, such as through a chimney. Centralizing the heat source for several rooms led to the concepts of heat transfer, heat exchangers, and heat distribution. Chimneys are still needed to vent the fairly hot exhaust after it has passed through the heat exchanger.
To increase efficiency, heat exchangers were lengthened (to capture as much heat as possible), which in turn resulted in cooler exhaust that could now be vented through a wall. Better control of combustion air also improved efficiency. But the cooler exhaust tends to condense, requiring a drain mechanism.
Applying General Heating Concepts to Heating Water
In gas and oil hot water heaters, the fire occurs below the tank, with exhaust passing by a heat exchanger up through the tank center. (I.e., the heat is transferred to the water in the tank.) In an electric water heater, elements in the tank make the water hot directly. The various methods to improve efficiency have been applied to all technologies.
Be Alert to the Potential Dangers of Hot Water Heaters
Familiarize yourself with the key elements of your water heater. The cold intake usually comes into the top of the tank and should have a water shutoff valve. There should also be a shutoff for fuel or power. Find the thermostat and check its setting; I recommend keeping the water temperature no higher than 120°F. Near the bottom of the tank should be a drain valve.
Now the most important part is the temperature/pressure relief (TPR) valve. It is designed to open when temperature exceeds 210°F or the pressure exceeds 150 psi. If this valve is missing or installed improperly, the tank is in danger of exploding and causing major damage. If you have any safety questions, contact a plumber or schedule a home inspection.
Weighing the Options
Every technology has its requirements and tradeoffs. Tank size is inversely proportional to recovery rate. If space is tight, tend towards technologies that don’t require frequent access or high volume of surrounding air. If high efficiency is desired, make sure your house can accommodate the condensate drain and/or direct venting needs.