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Ask Mr. Tight-Watt: Geothermal Heat Pump Fans  Smart Choices Archive

Ask Mr. Tight-Watt: Geothermal Heat Pump Fans

Mr. Tight Watt answers a reader's question about geothermal fans.

Ask Mr. Tight-Watt

Question: My HVAC contractor who works on my geothermal heat pump says I should keep the fan on the pump running 24/7 to circulate air in my home. I heard that this is not good for the system. Is this correct? If that's the case, what’s the best way to keep air circulating in my home? —Robin, a Smart Choices reader

To answer this question, Mr. Tight Watt asked for advice from Steve Anderson, a geothermal specialist formerly with the Iowa Geothermal Association.

Steve’s Answer: There is very little detriment to the HVAC system by running the blower fan 24/7. In fact, constantly circulating the air has two main benefits: air quality and comfort. Moving air continually through the air filter or other indoor air quality devices incorporated in the air delivery system means the air quality in the home will be at it best. Hot and cold spots in the home are reduced as the constantly moving air mixes different air temperatures, which means the air temperature throughout the entire home is more constant and consistent.

Most of the premium models of geothermal equipment are equipped with ECM (electronically commutated motor) blower motors or “variable speed” motors. This allows the motor to change the blower output as its speed increases and decreases.

From an energy standpoint, a reduction in blower motor speed results in an exponential reduction in power or energy (kWh) consumption. When a geothermal heat pump is equipped with an ECM blower motor and has a “constant fan” option, the blower output is in the range of 500–700 cfm or a reduction of 50–70 percent from the output when the geothermal unit is heating or cooling. The blower output reduction is a result of a 50–70 percent reduction in the speed of the ECM blower motor, which results in perhaps a +90 percent reduction in power consumption. In other words, a homeowner can operate the geothermal heat pump’s ECM blower motor in a “constant fan” setting (24/7) and the energy cost will be pennies per day: an ECM constant fan has a monthly operating cost of only $3–$4 per month. On the other hand, a constant fan with regular (PSC) blower motor will cost +$25 per month to operate.

Note: It’s not feasible to retrofit a blower motor from a PCS to an ECM because not only would the blower motor need to be replaced, but also the controls, such as the circuit board, controller, and thermostat.

If you are not sure which type you have and can’t reach your installation contractor to ask about it, check with a qualified service contractor, because identification requires removing panels to gain visual access to the blower compartment. 

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