When my air conditioner runs, I can feel hot air coming from it outdoors. Can I capture this heat for my hot water? Also, is there anything to make it dehumidify better?—Kyle L.
Air conditioners don’t actually cool the air. What they really do is move indoor heat outdoors. There is more heat overall because the electricity used by the air conditioner ends up as additional heat outdoors.
Several devices you can install use the air conditioner’s waste heat to warm your hot water. Others make your central air conditioner more efficient, improve comfort, and reduce allergies.
Desuperheaters connect your central air conditioner hot condenser coils to the water heater tank. Instead of the condenser coils giving off the heat to the outdoor air blowing past them, they heat the water inside the water heater tank.
One common method uses a sealed coil inside the water heater through which the hot air conditioner refrigerant flows. Another uses a separate heat exchanger to heat the water. Some simple models have the heat exchanger built into a circular base upon which your water heater rests. Built-in desuperheaters are common on geothermal heat pumps and can be used with standard heat pumps.
Add-on or integral heat pump water heaters (HPWH) are efficient devices that both heat your water and cool and dehumidify whenever they are heating the water. This reduces the amount of time your central air conditioner has to operate, so you save electricity overall.
HPWHs draw their heat for the hot water from the air in your utility room or basement. Instead of having the hot condenser coils outdoors, the HPWH has a built-in heat exchanger, which is connected to your water heater.
An HPWH operates two to three times more efficiently than a standard electric water heater, so your water heating costs are reduced by about half. With the added advantage of its dehumidification, you can set your central air conditioner thermostat higher without sacrificing comfort.
Several of the add-on HPWHs are easy to install yourself. A valve is attached to the standard drain valve near the base of your existing water heater. The HPWH can be placed on the floor or mounted on the wall. If you want the cool, dehumidified air in another room, you can duct the output air to an adjacent room.
Another add-on HPWH style is circular and designed to mount on top of your existing electric water heater. This generally requires professional installation, but it saves floor space. Complete integral HPWH models that include the entire electric water heater tank are also available.
There are also some devices that are effective for improving comfort while lowering your air-conditioning bills. If you have an old central air conditioner and you have made your home more efficient over the years, it is probably oversized now. This results in a cool, clammy feeling inside your home because it does not run long enough to adequately dehumidify the air.
Installing a dehumidifying heat pipe can cure this problem. Using simple heat pipe technology developed by NASA, the coil super-cools the return air to increase dehumidification. This heat energy is reintroduced into the air on the other end of the heat pipe. The final output air is slightly warmer but much drier for better comfort and less mold and allergies.
New super-efficient whole-house dehumidifiers are also money-savers. They can be attached to the duct system and bring in filtered fresh outdoor air during the summer. If the air is drier, you can set the thermostat higher.
Write for Utility Bills Update No. 458, a guide of water heater manufacturers. Include $3.00, a business-size SASE, and Update number. Mail requests and questions to James Dulley, Kentucky Living, 6906 Royalgreen Drive, Cincinnati, OH 45244. Go to www.dulley.com to instantly download.