Water heaters are rated by the number of gallons of water per minute (GPM) or per hour (GPH) that they can raise 100 Degrees Fahrenheit. This measure applies to all water heaters, regardless of their construction or fuel used.
So by definition if we can increase the incoming water temperature to our heater:
- The output water temperature can be increased (subject to a safe temperature limiting), or
- The volume of controlled temperature water output can be increased, and
- The total effective capacity of any heater can be increased.
Domestic water entering your home (or business) is always significantly colder than the environment it is entering. Thus as an example you must let the water run a while before it gets cold to pull the cooler water from the outside the building (underground) water source. The effect is similar with the hot water heater supply piping, subject to the limited water piping capacity within the building. When the cooler water reaches the water heater it has to work harder to elevate temperature. Therefore by increasing the amount of building environmentally warmed water to the heater we increase performance and save energy.
By placing a non-insulated tank of water between the water service entrance and the water heater we allow a larger volume of water to acclimatize (temper) to the ambient temperature at its location, thus a “Tempering Tank”. Its construction and configuration are simple:
- A somewhat taller than wide tank with two pipe openings, one near/at the bottom and the other near/at the top. Its interior finish must be compatible with passing potable (sanitary) water through it safely.
- The incoming water is piped to the bottom and the outgoing from the top of the tank. Hot water rises and therefore the warmer water stays substantially at the top while the colder replacement water enters the bottom. Water diffuses within itself, but at a typically lesser rate than used, protracting the effect.
Practically, any water heater or water storage tank stripped of insulation and being glass, stone or otherwise lined for water cleanliness is suitable. There are other options as well, typically used for well pumps and wet processes. So, look around for an opportunity.
Note: One point to remember is that the temperature differential and flow of cold water can cause these tanks to “sweat” (condense moisture on the lower exterior of the tank). The simple solution is to provide a larger pan under the tank with an inch or so of coarse sand in it. It will absorb and then evaporate the condensation effectively.
Please accept that this is not a cure all for a too marginal heater or a plugging boiler or heater coil. The latter will surely get worse over time. But it helps save energy in the meanwhile.
This “trick” is nothing new. We sometimes refer to them as “Farmer’s Tanks” when found in older homes.
It’s a great Do-It-Yourself (DIY) Project. So that old electric water heater with the burned out elements that you just haven’t disposed of yet may have some life left in it after all.
Last Edit: 10/10/2012 pdm