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Heat Pump Basics

If you have an all-electric home, are wary of propane costs, want to avoid combustion in the home, and/or want to be able to both heat and cool your home with one unit, a heat pump is worthy of consideration. The two main types of central heat pumps to choose from are air source heat pumps (ASHPs) and ground source heat pumps (GSHPs).

Air Source Heat Pumps

ASHPs work similarly to air conditioners but can heat when flowing in reverse: heat is removed from the outdoor air and transferred to the refrigerant flowing through the condenser before being released into the home through the unit’s indoor air handler and ductwork. A drawback with ASHPs is that some residential units become inefficient when trying to remove heat from outdoor air when it’s less than 40 degrees F. (They rely on electric resistance coils or gas furnaces to provide backup heat.) Since even daytime winter temperatures of less than 40 degrees F are common throughout Colorado, it’s important to consider a cold climate ASHP when shopping. Cold climate heat pumps have been shown to extract heat from air as low as -13 degrees F. If considering an ASHP, you’ll want to look at the unit’s heating season performance factor (HSPF) and seasonal energy efficiency ratio (SEER) to determine its efficiency. The most efficient units have HSPFs between 8-10 and SEER ratings between 15-18, and can deliver 1.5 to 3 times more heat energy than the electrical energy they consume when installed properly with the correct amount of refrigerant charge.

Like conventional ASHPs, ductless mini-splits have both an outdoor condenser and indoor air handler for both heating and cooling. The difference is that the air handler is not connected to a network of ducts but instead distributes conditioned air directly into a space. Air handlers can be mounted to a ceiling, inside a dropped ceiling, or to a wall. Multiple air handlers can distribute conditioned air from one outdoor condensing unit into multiple spaces or zones, and the air handlers are connected to the outdoor condenser via conduits. An advantage of these systems is that energy will not be lost in transport from the outdoors to the indoors as is often the case when heating or cooling through ductwork. Drawbacks of these systems include their high upfront cost and a limited pool of qualified installers/servicers in some parts of the state.

Ground Source (Geothermal) Heat Pumps

GSHPs transfer heat with the ground instead of the outdoor air. Coils of pipe run from the unit’s indoor pump underground – either horizontally at least 6 feet underground or vertically 250 feet or more underground—in a “loop field”. Horizontal loop fields require more space but can be less expensive to install than vertical loop fields. GSHPs can be considerably more efficient than ASHPs, don’t necessarily require backup heat, and can heat either air or water to run through the home. On the other hand, they are also significantly more expensive and land-intensive to install. Like ASHPs, the success of the system depends largely on the quality of the installation. If using electricity from Colorado’s grid to power the pump, greenhouse gas emissions from GSHPs may or may not be less than emissions associated with high efficiency natural gas furnaces. Maintenance of both ASHPs and GSHPs should include regular tune-ups from qualified technicians and cleaning or replacing filters every month or as needed.

Last updated: August 17, 2018 at 16:15 pm