Zombie Heat Pumps: The Reason Your Electric Bill Went Up

Couple Who Look Confused While Looking at Their Electric Bill

Understanding Zombie Heat Pumps and Increased Electric Bills


How Zombie Heat Pumps Affect Your Electric Bill

If your air conditioning goes out in the middle of the summer, you realize it pretty fast as the house heats up.  But if your heat pump is not operating properly in the winter, you might not realize it – until the electric bill shows up!  That is because heat pumps usually use electric backup resistance heaters, which use more electricity to produce heat than the heat pump.  For an energy-efficient home, let’s explore how this works.

Heat Pump Operation and Efficiency

A heat pump takes heat from outside and moves it inside your house.  Even cold winter air contains some heat, and heat pumps can extract heat from the outside air on a cold day and transfer it indoors to maintain a comfortable temperature.  It does this by operating as a refrigeration system – essentially an air-conditioner running in reverse.  If the heat pump is taking heat from the outside air (as opposed to a geothermal ground loop), the efficiency of the heat pump decreases as the outdoor air temperature decreases. The colder it is, the harder it gets to keep your home comfortable.

The efficiency of a heat pump varies significantly with the outdoor temperature. While a heat pump may be twice as efficient as a conventional heating system at 50 degrees F, when the outdoor temperature drops to less than 30 degrees, supplemental electric resistance heating kicks in.

Electric Backup Heaters and Supplemental Heating

At very low outdoor temperatures, the heat pump compressor will shut off completely and the backup heating system takes over – using much more electricity.  Most smart thermostats support many stages of heating and cooling and can run the heat pump and auxiliary heat simultaneously to maximize comfort and reduce overall energy costs.

Smart Thermostats and Energy Optimization

In case of compressor or general system failure, many thermostats have an emergency heat switch that bypasses the thermostat and activates the supplemental heater.  You may have noticed that after a power outage, the supplemental electric resistance heater runs for a while to heat the house.  This is normal, as the system is designed to reheat the oil in the crankcase of the compressor before restarting the compressor.

Troubleshooting and Maintenance

If you notice that your system is heating but the outdoor compressor is not running, or if the emergency heat light is on, there could be several reasons for this.  The power might be off to the outdoor unit because of a blown fuse or tripped circuit breaker.  A very dirty air filter, or debris on the outside unit (such as snow) could also be the problem.  Drastic changes to the settings on the thermostat might also force the system into emergency heating mode.

If the auxiliary or emergency heat light is always on when the unit is heating, there is probably some problem with the system.  A service professional can quickly check if the system is low on refrigerant, or if there is a more serious problem.

Keep an eye on your thermostat light and your system, as well as your electric bill.  If there is an increase in electrical usage for no apparent reason, you may have a zombie heat pump running on expensive backup electric resistive heat.

Read Next: Four Steps to Keeping Your Home Comfortable and Energy Efficient This Winter

Keep your home comfortable in winter


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13 thoughts on “Zombie Heat Pumps: The Reason Your Electric Bill Went Up

  1. My miller furnace sometimes will not ignite the gas when suppose to. The blower motor still turns on as it thinks it to heat the house but it sounds like the ignitor does not light the thermostat to light the gas. I have replaced the ignitor and thermostat and still when I come home from a vacation the house is 45 degrees when calling for 70? Any suggestions. Mod.# G3RC100C-20

    • Hi Al, If your blower turns on when there is a call for heat it tells me the thermostat is operating. What you wish to determine is if the lighting of the burners is an occasional issue or is it happening consistently.
      While you are standing in front of the furnace have someone turn up the heat set point on the thermostat to start the sequence for ignition. Just observe what occurs.
      1- The ignitor should start to glow a bright red as it heats up. The typical warm up time is 17 to 45 seconds.
      a. If it doesn’t glow the ignitor may need replacement.
      2- After 17 to 45 seconds you should hear a click from the gas valve and the gas will be ignited.
      a. If there is ignition of the gas but it only stays lit for 5 seconds or so and then shuts off the likely problem is the flame sensor. The flame probe will need to be cleaned and polished with a “scotch brite” type cleaning pad or 00 steel wool till the surface is shiny.
      b. If after cleaning it continues to lockout after 5 seconds it will require a qualified HVAC technician to replace the flame probe and inspect the wiring.
      3- If, on the other hand, you hear a click from the gas valve and occasionally it will not light the gas burners it may be something as simple as moving the ignitor over a ¼” to be more centered on the burner it is trying to light. Locating an ignitor out of the “sweet spot” for ignition can lead to not lighting the burners consistently.

  2. my heater wont start my husband cleaned filter now it wont turn on we haven’t used until now we we turned it off it worked air was working all summer is there anything I should look for is it something he bumped? is it something simple? please help thank you

  3. with our unit, when running the air conditioner I noticed that the air would turn warm like the heater was blowing not the air. I shut the unit off for several minutes and then turned it back on and it was blowing cool air again. It does this off and on continuously. What could be causing this?

    • Hi Tina. Based on the information you have provided, there could be a possibility that your system might have a leak and may have lost some of the refrigerant. If the system has lost charge and is tripping on internal overload protection and it is starting to enter a “loss of charge” failure mode. We would suggest that you hire a certified HVAC technician and have your system check.

    • Hi Jerry – It is not clear from your description as to where the rings are and how big they are. Sometimes frost can show up from time to time as a heat pump cycles but this should not last long or build up over time. In addition, if your heat pump is running on auxiliary heat on a relatively mild day that might be an indication that it needs to be repaired or at least serviced by an HVAC contractor to make sure it is operating properly.


    • I am having the same problem now. As compressor runs, but not fan, Frost builds up on outside unit. Once it stops, Frost eventually goes away, them compressor cuts back on

      • John, your unit may be going through a defrost cycle where the compressor will run with the fan off in a reverse cycle to clear the frost off the outdoor unit. It would then switch back to heating mode and start the compressor. If you feel that this is not what is happening we would suggest contacting a HVAC contractor to troubleshoot.

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