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When you think “heat pump” you probably associate the words with cozy winter warmth, not a coat of frost covering your outdoor heat pump unit. How can a unit that’s dusted with frozen water vapor generate heat to warm your house? There must be something malfunctioning.

Probably Not, But Maybe Yes

Don’t jump to conclusions just yet. Heat pumps extract latent heat from outdoor air through a coil circulating refrigerant, concentrating heat energy with a compressor, then conveying it into the house. When moist, cold winter air makes contact with the outdoor coil, the temperature variance between the two causes water vapor to condense out of the air. Since the refrigerant circulating inside the coil is usually about 20 degrees colder than air temperature, that condensation may turn to frost.

What To Do

  • First, check back in an hour or two to see if the frost is still evident. Heat pumps incorporate an automatic defrost cycle that melts frost away at regular intervals when the unit senses outdoor temperatures dipping low.  
  • If frost persists for more than two hours, or if it increases to a thicker coating of ice, you may have other problems. Rule out obvious causes, like leaves and other debris, obstructing free flow of air into or out of the outdoor heat pump unit. Also verify that you’re not simply seeing the accumulation of natural precipitation like falling sleet or freezing rain, or water dripping from a leaky gutter overhead, and then freezing.  
  • Remaining issues, like a possible refrigerant leak or component failure, can only be addressed by a qualified HVAC professional. In most cases, a heat pump will activate backup supplemental heating coils while the defrost cycle runs, so you may still feel warmth coming from the system indoors. However, electrical supplemental heating will dramatically increase your monthly operating costs, so the problem should be resolved ASAP.

If you’re in need of a professional to resolve outdoor heat pump unit issues in Fairfax, contact Brennan’s Heating & Air Conditioning.