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Matthew, HVAC Technician
Category: HVAC
Satisfied Customers: 2014
Experience:  14 years experience in the HVAC field of service, installation, Manual J & D calculations
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My heat pump runs continuely when the temp is 40 or below.

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My heat pump runs continuely when the temp is 40 or below. It does not swtich to auxilery heat or shut off. I have had several tech change the thermostat in the house but can't figure out what is wrong with the system

If the auxiliary heat strips are not coming on to help the heat pump during these cold temperatures then it will run continuously because it can not keep up with he heat loss of the structure.


Heat pumps are rated and tested at 47 degree outdoor temperature and 17 degree outdoor temperature.


At 47 degrees a 5 ton heat pump will produce 52,000 BTU of heat

At 17 degrees it will produce 33,000 BTU so it needs the help of the electric auxiliary strips in the furnace to help produce the extra BTU's to keep the house up to temperature when it gets cold.


Have they tested to see if your strips are working? What type of thermostat do you have on the wall? Does your thermostat have the ability to switch to emergency heat, and if it does do you get heat out of the vents when you switch it to emergency? Have they checked the refrigerant charge of the heat pump to see if it is producing the correct amount of BTU?

Customer: replied 7 years ago.

The strips are working. It is a honeywell thermo and was tested to swtich to auxil. When it is on em heat/auxil there is heat coming out of the vents. The refrigerant was checked. We have done all of this.....but last night the system ran nonstop. Today I monitor it and it ran not stopping but for a minute or two. It switched to auxil one time and that was in the a.m. the rest of the day it was in heat on mode. Now at 2:38 this afternoon it did shut off for approx 4 min and then came back on in the heat mode. Current temp is 44. Any other suggestions?


If the refrigerant charge is good and the the strips work then I would have to say that it is just running to keep up with the heat loss of the house. How old is the house and how is the insulation, windows and doors age, and other factors that would influence heat loss. The aux strips should come on 3 different ways.


1. The heat call is 4 or more degrees over the current temperature displayed on the thermostat


2. The heat is on for (normally 8 mins but it varies for each stat nd piece of equipment) with a 3 degree or less heat demand and still has not reached temperature


3. The heat pump goes into defrost while in a heat demand of 3 degrees or less.


Take a temperature reading and see what you are getting out of the registers a good rule of thumb is with heat pump only heat it should be about 50 degrees over the outdoor temperature coming out of the register and for heat pump+aux it should be about 60 degrees over the outdoor temperature.

Customer: replied 7 years ago.

We purchased the house 4years ago in May. It was built in the late 70's. The windows are replacement-done approx 7-8 years ago. We did just weather strip the front door. The heating/cooling unit was replaced less than 3 yrs. Our temp got down to 10 last night. The unit did not shut off once We have two separate units one for the upstairs and one for the down stairs. They are both set at 67. The upstairs unit ran some then shut off. The downstairs unit ran either on heaton or aux. It did not turn off one time. At the current time 9.28, it is 18 and the unit still in running on heat on / aux- more on aux than in the past days. How cost effective is it to run the unit? I have checked that the unit did not freeze up because we have had that happen has not froze up. I understand it will run more in extreme cold. However, my electric bill was over 600 dollars last month......I'm trying to make sure this is functioning or do I have a problem somewhere. Thank you for your help.


Your unit is just doing everything it can I am afraid. Heat pumps are not designed to work in these temperatures. Most of the time when they are installed in areas where it gets this cold they are installed with a duel fuel setup so that you can switch to gas heat when the temperature's dip below freezing.

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Customer: replied 7 years ago.

Thank you Matthew. I guess I need to look for alternative heat....pellet stove when the temp are extremely cold. I appreciate you help.