Heat Pumps in Cold Weather — What You Should Know

When discussing the operation of heat pumps in cold weather — what you should know is that at some point they become inefficient or worse, ineffective.  In this article we’ll look at how heat pumps work in cold weather and offer suggestions for keeping warm as the temperatures fall.

Most heat pumps maintain their effectiveness down to roughly 30 degrees.  It varies slightly from model to model but that’s a ballpark figure that is within a few degrees for most heat pumps.  If your heat pump is properly sized for your home, at roughly 30 degrees it won’t be able to maintain the temperature of your home at the 68-72 F that most of us like.  Things will get worse as the temperature gets colder.  Of course, if your heat pump is much too large for your home — a 5 ton unit when it should be 3.5 tons — than it will keep up longer.  However, you’ll have serious problems with an oversized unit that include energy waste, poor dehumidification when cooling, and probable mechanical problems from running short cycles.

For using heat pumps in cold weather — what you should know is that you have 2 options based on your climate.

1. In moderate climates, add one or more heat strip.  A heat strip is like the heating coil in a space heater.  It uses electricity to create heat which supplements that which is produced by the heat pump.  Heat strips are installed in the air handler.  The heat strips activate when the heat pump is operating and the heat is blown into the home by the blower. They are typically 5 or 10 kilowatt each and an air handler may have up to 20 kilowatt of heat strip capacity.

Heat strips also provide emergency heat when a heat pump is not working properly.  Most systems have an emergency heat mode that energizes the heat strips and activates the blower.  These heat strips don’t make enough heat to replace the heat pump, but they will make it more comfortable until you can get the heat pump serviced, and they may keep pipes from freezing in extreme cold.

2. In cold climates, consider a dual fuel heat pump.  A dual fuel heat pump may also be called a hybrid heat model.  Dual fuel heat pump split systems use a gas furnace instead of an air handler.  The homeowner can set the temperature point at which the system switches from heating with the heat pump to heating with the gas furnace.  This temperature point is usually between 30 and 40 F.

The value of a dual fuel system is that it makes a heat pump a viable choice even in cold climates.  Some may ask why a homeowner wouldn’t skip the heat pump and install an air conditioner/gas furnace split pump instead.  The primary reason is that heat pumps heat more gently and evenly than gas furnaces, and many people find this more comfortable and preferable.  The heat they create is at a lower temperature than the heat made by a gas furnace. The result is that the home warms up more gradually, giving heat time to reach all areas of the house before the thermostat shuts down the system.

Conclusion

Heat pumps today are much more efficient than they were 15 years ago.  They are now a very viable source of heat compared with earlier models, in some cases being twice as energy-efficient.  Dual fuel capability takes them to the next level of versatility and performance.  If you are considering heat pumps in cold weather — what you should know is that they make more sense than ever.

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