Heat Pumps and Extreme Cold–What’s the Problem?

Two residential heat pumps buried in snow

Heat pumps can be a very efficient solution for heating and cooling your home, but if you live in the D.C. area you are at the northern limits of their effectiveness. Extremely cold weather can affect heat pump efficiency. This is why your cousin in Michigan owns a furnace. 


Why doesn’t my heat pump work as well in really cold weather?

In the simplest terms, heat pumps cool or heat your home by transferring the heat in the air from one area to the other. In the summer your heat pump grabs the heat from inside your house and pumps it outside. This process is reversed in the winter — your heat pump grabs the heat from the outside air and pumps it inside. And yes, even in air colder than 32 degrees there is some amount of heat in the air. The issue is how efficiently can your heat pump capture that heat in the cold air. To understand why that’s a problem we need to take a quick peek into weather maps…

Are heat pumps a southern thing?

Manufacturers design heat pumps for use in regions that don’t experience long spells of frigid temperatures. Your heat pump heats your home best when the outside temperature is between 55° and 35° Fahrenheit. In fact, your heat pump is designed to gather heat when the air temperature drops to 10°! It just can’t do it as efficiently.

The D.C. area is in the northernmost recommended area for efficient heat pump use since our region experiences several winter days below 35°. A glance at this map of average winter temperatures in the U.S. highlights these temperature zones.

As you can see, our area’s average winter temperatures are 30° or above. This means heat pumps can handle most D.C. winters. However, over the past few winters we have dipped to these lower extremes of 10° or below.

How does a heat pump cope with colder temperatures?

Heat pumps need to work harder to capture heat from that cold air. They also capture the heat generated from the compressor motor to help warm the air. Heat pumps grab the heat from wherever they can to run as efficiently as possible. When it gets really cold they can heat your home, but not as efficiently as other solutions like oil or natural gas systems. Heat pumps deliver the air differently to heat your home.

The air from a gas furnace is higher in temperature (around 125°) and feels very warm coming out of your vents. A heat pump’s air is lower in temperature (around 107°) and feels cooler. Now, 107° is more than warm enough to heat your home (unless you’ve set your thermostat to 108°) but some people think it feels drafty while others prefer the less intense temperatures of a heat pump. So, while it may feel as if the air coming out of your vents is not hot, it is probably the correct temperature, your heat pump is just working as efficiently as it can to keep your home at your set temperature.

Don’t worry, if it gets really cold outside your heat pump has a solution to help keep you warm.

It’s, like, zero degrees out there! How is my heat pump going to push warm air into my house?

The answer is that the heat pump comes with a heating component to assist with warming the air. Known as “auxiliary heat,” or “emergency heat,” an electrical heating element turns on when the temperatures are too low for the heat pump to effectively gather all the heat from the cold air. While this will help warm the air it comes at a substantial cost by using almost three times as much energy as the heat pump alone.

My heat pump looks like the inside of my grandmother’s freezer!

It is normal for a heat pump’s coils to gather white frost, or even ice, on some winter days.

Don’t worry, the heat pump will cycle into a defrost mode to de-ice the coils. The heat pump will reverse to air conditioning mode. Yes, the air conditioning mode. The outdoor fan will turn off and the outdoor coil will warm, melting the frost. At the same time, the auxiliary heat will turn on to warm the cold air blowing through the vents. When the coils are clear the heat pump returns to the heating mode. You may hear the fan turn on and the sound of the refrigerant changing direction in the system. The process normally takes under 10 minutes.

Malfunctioning Heat Pump covered with excessive snow frost

Common issues with heat pumps in winter.

The heat pump is filling with ice.

This is normal on some winter days. Frost or ice collects in the coils on the sides of the unit. The heat pump has a programmed cycle to defrost the unit and return to normal operation. If you see ice forming on top of the unit or building up around the unit without defrosting, this may be an indication of a problem. You should call for service to prevent the unit from being damaged.

A few things NOT TO DO.

  • Do not pour hot water in an attempt to defrost the unit. The extreme temperature change can damage the equipment.
  • Do not chip at the ice with a sharp or hard object. The coils and fins are delicate.
  • Do not let leaves or snow pile up around the unit. The heat pump needs good air flow to operate.
The fan is running but the air isn’t hot.

Heat pumps use a milder heat than furnaces. This allows them to run more efficiently. The air may not feel hot, but it is warm enough to keep your house at temperature. However, if the air feels cold, and it is very cold outside, your auxiliary heat may not be operating correctly.

The heat pump is making weird noises.

If the weird noises happen infrequently you may be noticing a defrost cycle of the heat pump. The refrigerant runs in opposite directions in this mode and the fan turns on and off. If the noises are new and constant, your heat pump may need service.

Parts of my house are colder than others.

This may not be a heat pump issue. See our post on uneven heating. Proper ductwork and airflow are more important than the type of heat your system generates. Issues with airflow can affect the efficiency of your heat pump and problems with the ductwork can affect the comfort of certain rooms in any season. One item you can check is your air filter. If your air filter is dirty, clean or replace it to maintain proper airflow.

Contact us for your Seasonal Heat Assessment.  We serve Northern Virginia (Fairfax, Arlington, Alexandria, Woodbridge, Vienna, Springfield, Burke, etc.), Washington, DC, and Suburban Maryland (Rockville, Potomac, Silver Spring, Laurel, College Park, etc.)  Our technicians will evaluate and test 32 different components for proper functioning and give you a completed report card on your system’s performance.  Call us at 703-750-4008.

Corey Rodgerson

Corey is a third-generation HVAC technician. Both of his grandfathers started in the trade in its infancy and both of his parents continued the tradition with Climate Heating & Cooling. Corey has earned master's licenses as an HVAC Mechanic, Electrician, Gas Fitter, and Plumber. He has been certified in lead remediation, building performance through BPI, and he has completed five NATE certifications for service and installation of HVAC units. He is committed to training and deploying the best technicians in the industry.

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