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Heat Pump Or Resistance Furnace - Which Do You Want To Turn On?

Heat pump or resistance furnace - which one do you want to turn on?

A heat pump provides heat two ways:

1.  The mechanism is essentially an air conditioner with the ability to work backwards.  To heat a house it literally compresses the heat from outdoors and brings it inside.  When it's too cold outdoors the heat pump becomes less efficient, and eventually unable to provide heat.  So,

2.  There is a resistance furnace to help it.  The resistance furnace is a big toaster.  Electric coils heat up and air blows over them to heat the house.  The resistance heat is 100% efficient, but much more expensive than heat pump heat.

To turn on the heat pump the thermostat button should be set on "HEAT."  You can see in the photo that the button here was set on "HEAT."  When in that position only the green light should come on.

If the heat pump breaks the resistance furnace can be turned on so the house can be heated while one waits for the compressor to be fixed.

In that case the thermostat button would be set to Emergency Heat, sometimes called Supplemental Heat.

When the button is set in that position the red light should also come on.

But when the button is set on "HEAT" both lights should NOT come on!  In this house both lights did turn on, as indicated by the yellow arrows.

The resistance furnace provides much warmer heat than the heat pump alone would blow from the ducts.

So, is the problem here that the old, analog thermostat is broken and both lights are merely coming on, or is the resistance furnace actually turning on?

Mighty Mo saw that the heat in the duct just over the unit was very warm, too warm for just the heat pump to be providing heat alone.

The heat pump compressor was operating at this time, so it did turn on as demanded.  And we see that the resistance furnace must also be on as the temperature just above the unit is so warm.

My recommendation:  this was an older unit and an older thermostat - the plaque said 24 years.  The heat pump compressor's life span is about 12 - 15 years.  But that is not hard and fast.  Their life span depends on maintenance and care.  When the compressor is broken heating the house is very expensive!  And many homeowners would not know.  I have inspected houses in the past where the resistance furnace was always operating at the same time as the compressor and find out that one reason the people were selling the house was because the electric bills were so high!



Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560


Comment balloon 7 commentsJay Markanich • March 20 2017 10:54AM


I didn't know this, probably because I've never used a heat pump or resistance furnace. Good information to hold onto. Have a great week, Jay!

Posted by Nathan Gesner, Broker / Property Manager (American West Realty and Management) over 3 years ago

Good morning Jay. Had a home with an early generation heat pump! Must say, was not a fan! Enjoy your day!

Posted by Wayne Martin, Real Estate Broker - Retired (Wayne M Martin) over 3 years ago

I hope so, Nathan!  We try to inform.

Wayne - I get it!  The gas company ads still use the idea that heat pumps blow "cold" air, around 90F which is about skin temperature, so the air felt cold.  But the newer units are much more efficient and blow air that is comfortable now.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 3 years ago

Heat pumps are not used here in New Mexico, but when I was in Florida they were prevalent. You can always tell when the heat strips come on because the dust that settles on them smells for a bit as it burns off. If that compressor goes out... it is indeed an emergency!!

Posted by Fred Hernden, CMI, Albuquerque area Master Inspector (Superior Home Inspections - Greater Albuquerque Area) over 3 years ago

When I test the heat in autumn and it's the first time the heat has been on I can demonstrate to buyers that distinctive smell, Fred!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 3 years ago

Reminds me of the time I upgraded our analog thermostat to a digital WiFi unit.  First round I wired it incorrectly and that night we had emergency heat all night.  I was so used to feeling a lower temperature heat coming from the registers, I knew something had to be wrong!

Posted by Stephen Weakley (Nationwide Mortgage Services) over 3 years ago

It seems only right that you should have gotten a thank you card from the electric company, Stephen.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 3 years ago

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