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"Geothermal heat pumps for lowest utility bills, best comfort"

Dear Jim: I should replace my old heating/cooling system with a more efficient one. With gas prices going up, shortages of propane, etc., is installing a geothermal heat pump wise and what types are best? - Shel K.

Dear Shel: Making the significant investment in installing a geothermal heat pump does make sense. Keep in mind, a geothermal heat pump also becomes the most efficient central air-conditioning system during summer and provides free water heating.

I just replaced my old heat pump with a WaterFurnace 7-Series geothermal heat pump in my own home. Even though the overall installed cost is higher than other systems, it will pay back its cost in savings and the comfort level is excellent. Also, if one is installed by 2016, there is a 30-percent Federal tax credit on the total cost.

I chose this WaterFurnace model because of its superhigh heating and cooling efficiencies. It has a heating efficiency COP (coefficient of performance) of 5.3. Using the constant temperature underground, it produces more than $5 worth of heat for each $1 on my utility bill. When cooling during summer, the EER (energy efficiency ratio) is as high as 41. This is more than twice as efficient as the best new standard heat pumps and central air conditioners. Instead of the heat from the house being exhausted through the outdoor condenser unit, it goes into the water heater for free heat.

For most homes, several five-inch diameter holes are drilled about 150 feet deep for the tubing to use the Earth's heat. This is called a vertical loop. I have a large backyard so I installed a long horizontal, five-foot-deep loop. The loop replaces the outdoor condenser unit so there is no noise to bother you or neighbors. The indoor compressor is very quiet.

The 7-Series model, because it uses a special variable-output compressor, fine tunes the heating and cooling output to the instantaneous needs of my house. This is the most expensive system design, but it provides the best savings and year-round comfort. The installation cost of the ground loop is the same no matter what geothermal system you install.

By constantly varying the output, it runs in more efficient slower, quieter cycles and the air from the register feels hot. A common complaint for standard heat pumps is it never feels warm. The energy-guzzling backup resistance heating seldom, if ever, comes on. During very hot weather, the compressor can run in supercooling mode to produce an extra 20 percent output.

The next step down in comfort and efficiency is a model with a two-stage compressor. Most of the time, it runs at the lower-output speed. When it cannot heat or cool your house to the thermostat setting, it automatically switches to the higher speed for more output. Its EER is as high as 30. The simplest design is a single-output compressor which either is on or off. This still provides much better comfort and savings over a standard heat pump.

Dear Jim: We have adequate blown-in insulation in the attic. I can get some free R-19 fiberglass batt insulation at work. Would it make sense to staple this insulation up under the roof sheathing between the rafters? - Dan H.

Dear Dan: Unless you need to control the attic temperature for some reason, adding the insulation will not make any difference. If it is unfaced, just lay it over the existing floor insulation to get some benefit from it. A better use of the insulation is to wrap around your water heater. If your water heater is gas, make sure to leave clearance for the combustion air and flue draft. Wrap reflective foil over the insulation.

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