Hot Water Tanks
This section discusses:
Why you should be concerned over the type of hot water tank chosen for your house
As houses become more energy efficient, the demand for space heating energy is reduced. As a result, in a new home, the energy used by the hot water tank represents an ever-increasing percentage of the overall energy bill. In some smaller, very efficient R-2000 homes, the hot water tank uses as much energy as the spacing heating equipment in the house.
The proper selection and installation of your hot water tank can save energy dollars.
Reducing energy losses in domestic hot water systems
Reducing standby losses
A typical hot water tank is actually used for only about two hours a day. It sits idle for the rest of the time, giving off its heat to the surrounding space. Increased levels of insulation surrounding the tank will reduce these standby losses.
Both natural gas fired and electric hot water tanks are available in various models with differing levels of insulation. The least expensive tanks have about 1" of fiberglass insulation around the tank.
Mid-range tanks have about 1" of foamed in place urethane insulation around the tank for a higher R-value and less standby energy losses. These units also generally come with a longer manufacturer warranty.
The most energy efficient hot water tanks are supplied with 2" – 3" of foamed in place urethane insulation around the tank, allow minimum standby energy loss and come with the longest manufacture warranty.
 When installed on a concrete basement floor, natural gas hot water tanks should be placed on top of a piece of rigid insulation and plywood to reduce heat loss through the bottom of the tank. In order to allow heat transfer from the burner, a gas hot water tank is not insulated on the bottom portion. Rigid insulation installed between the uninsulated tank bottom and the cold concrete floor will mitigate heat loss in this area.
Heat traps
Within a hot water tank, the warmer water tends to rise to the top and the cooler water will fall. The warmer water wants to keep rising and will do so up the hot water supply pipe leaving the top of the tank. Once the water rises up into the water supply pipe, it loses its heat to the room, cools and falls back down into the tank. This convective loop of water movement needlessly transfers excessive hot water heat to the room.
To limit this type of water movement and heat loss, a heat trap is installed. This simple trap restricts the convective movement of water and limits energy loss.
Reducing pipe losses
The best way to reduce heat loss from the pipe is to minimize the length of hot water pipe between the tank and the fixture served. This also saves on water consumption, as homeowners tend to run a hot water tap straight down the drain for the length of time it takes to get hot water to the fixture. Consider locating the hot water tank close to the bathroom and kitchen locations.
Pipe insulation should also be installed for at least the first three feet of pipe from the tank.
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