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Heat Pump It

I want to install the most efficient heat pump for lower electric bills. I am also concerned about getting one that provides the best year-round comfort. What features should I look for?—Bob M.

With the new minimum energy-efficiency requirements for 2006, there have been improvements in heat pumps that make them an excellent choice for almost any home. The prices of fossil fuels, such as natural gas, oil, and propane, are at record highs, so using a heat pump may be the least expensive source of year-round heating and cooling.

Your local electric co-op can give you excellent advice on the ideal heat pump for you.

Heat pump efficiency in the cooling mode is rated by SEER (seasonal energy efficiency rating), similar to a central air conditioner. In the heating mode, the efficiency is rated by the HSPF (heating seasonal performance factor). Generally, the ones most efficient at cooling your home are also the most efficient when heating. If you now have an old heat pump with a SEER in the 8.0 range, installing one of the most efficient (SEER of 19) new ones can significantly cut your utility bills.

Many HVAC (heating, ventilation, air-conditioning) manufacturers are starting to recommend hybrid heating, even in colder northern climates. Hybrid heating refers to installing a heat pump, instead of just a central air conditioner, along with a fossil fuel furnace.

During mild weather, the heat pump can be less expensive to operate than even the most efficient fossil fuel furnace. When the outdoor temperature drops, the furnace takes over. A heat pump of the same capacity, efficiency, and features may cost only about $400 to $500 more than the equivalent (cooling only) central air conditioner.

As a brief background, a heat pump is basically a central air conditioner with a reversing valve. When switching from the cooling to the heating mode, the reversing valve reverses the direction of the refrigerant. The hot gases flow through the indoor blower coil to heat the air inside your home. The wall thermostat takes care of automatically switching the reversing valve depending on whether you need heating or cooling.

A two-stage heat pump is your most efficient option. The heat pump has two different output levels when heating and when cooling. This allows the heat pump to be sized to handle some of the coldest or hottest days, yet also be effective during milder weather. Depending on the compressor design, the heat pump lower-output level will be from 50 to 67 percent of the maximum higher-output level.

This is a great advantage because the heat pump runs in longer, more efficient cycles when it is operating in the lower-output level. Even though it is running longer, the compressor is using less electricity in this lower-output level, so the overall electricity usage is reduced. By running longer and slower, there is less indoor blower and airflow sound, and indoor temperatures remain more constant.

Most HVAC manufacturers have switched to using a two-stage scroll compressor with R410A refrigerant instead of R-22 (commonly called Freon). R410A is more environmentally friendly than R-22 and it operates at slightly higher pressures. This requires more stout tubing, so the noise level from the outdoor unit is less noticeable. By 2010, manufacturers will no longer be allowed to produce units using R-22.

Most two-stage heat pumps use a General Electric variable-speed ECM blower motor in the indoor air handler.

One advantage of the variable-speed blower, when used with the proper thermostat, is in controlling indoor humidity. This impacts comfort and common allergens such as mold spores and dust mites.

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