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"Air-condition your house while heating your water for free"

Click here to see a descriptive illustration showing several devices to cool house while heating water

Dear Jim: When my air conditioner is running, it gives off a lot of heat outdoors. Are there any devices to capture this waste energy to heat my hot water for free? If so, can I install one myself? - Ron M.

A: You can heat your hot water for free using the heat given off from air conditioners. Air conditioners don't actually cool overall. Using a refrigeration cycle, they draw heat from indoor air and transfer that heat, plus the heat from their motors, to the outdoor air.

Add-on or integral heat pump water heaters (HPWH) are efficient devices to do what you want. These operate similar to a window air conditioner. They draw heat from your utility room or basement cooling the air inside your house.

Instead of having the hot condenser coils outdoors, the HPWH has a built-in heat exchanger connected to your existing water heater. When the HPWH is running, your house is being cooled and the water is being heated.

Overall, a HPWH operates three to four times more efficiently than a standard electric water heater so your water heating costs are reduced by up to 75 percent. An added advantage is a HPWH dehumidifies the indoor air for better comfort, less mold growth and reduced allergy problems.

Several of the add-on HPWH's are easy to install yourself. A special two-way valve is attached to the standard drain valve near the base of your water heater. The HPWH operates on 110 volts, so you just plug it in. It can be placed on the floor or mounted on the wall and the cool, dry air can be ducted to other rooms in your home.

Another add-on HPWH design is circular and mounts on top of your electric water heat. This generally requires professional installation, but it saves floor space. Complete integral models that include the entire water heater tank are also available. Desuperheater devices are available to connect your central air conditioner hot condenser to the water heater tank. This can be done with a coil in the water heater or a separate heat exchanger. Some simple models have the heat exchanger built into a circular base upon which your water heater rests. Built-in desuperheaters are common on whole-house geothermal heat pumps.

Other devices are effective for improving comfort while lowering air-conditioning costs. If you have an old central air conditioner, installing a dehumidifying heat pipe coil can help. This coil precools the room air to increase dehumidification for better comfort and electricity savings.

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.

Instant Download Update Bulletin No. 458 - buyer's guide of nine heat pump water heater (add-on and integral with tank), desuperheater, whole-house dehumidifying heat pipes and dehumidifier manufacturers, and other cooling/comfort and payback/savings tables and water heating efficiency tips.

Dear Jim: During last winter, whenever I took a shower and ran the bathroom vent fan, the fan dripped water a few minutes after I turned it off. What was causing this and how can I correct it? - Michael H.

A: You are most likely getting water condensation in the vent pipe that runs through the attic. At least this shows you have adequate attic ventilation so your attic is staying cold as it should.

You can run your vent fan longer so it exhausts all the moisture-laden air, but this will use more electricity. Try rerouting the vent duct in the attic to make it shorter and slope it downward to a soffit outlet.

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