Heat pump never quite reaches temperature:
In the Heating Mode:
In other words... if you set your thermostat for 71 degrees in the winter and your house only seems to get up to 69 degrees. This problem/situation is very common and it generates many service calls. And sometimes this is caused by a genuine problem, but unfortunately, in extremely cold weather, even a properly working heat pump may have trouble maintaining desired temperature.
Why is this? When it gets below a certain temperature, in our area - around 35 degrees, a heat pump loses efficiency and cannot keep up with the heat loss of the structure. When the temperature in the house drops approximately 2 degrees below room temperature, supplemental heat comes on to assist the heat pump (usually in the form of electric resistance heaters). When it gets to within 1.5 degrees of room temperature, the back-up heat cycles off and the heat pump continues running; trying to reach temperature, but cannot. This usually happens when the temperature is at it's coldest - 0 to 30 degrees.
Shown above: Supplemental Electric Resistance Heater Package
This is however, the way heat pumps are designed to operate. Even though they don't put out a lot of heat into the house, and they run for long periods of time, they are still quite efficient.
So, if it is very cold out and you desire your house to be a certain temperature, you might have to raise your thermostat by 2 degrees to maintain it. Now, if it isn't extremely cold out (above 35 degrees), and your heat pump is not maintaining temperature, this indicates a problem!
Below is a list of possible causes. Items in red usually require a service call. Items in blue however can be addressed, some even fixed by the homeowner.
Red = Professional fix | Blue = Homeowner fix
- Thermostat not calibrated/not level/faulty
- Low refrigerant charge
- Refrigerant flow-related problem - restriction/bad metering device
- Poor efficiency- needs cleaning and servicing
- Bad reversing valve
- Bad compressor valves
- Compressor not running
- Outdoor unit iced-up
- Snow drift against outdoor unit
- Outdoor unit not running
- Return duct leakage - pulling in cold, unconditioned air
- Open windows/poorly insulated house
The bottom five causes in blue are commonly found problems and can be addressed by the homeowner.
Here is a checklist to go through before requesting a service call:
- Make sure your outdoor heat pump is actually running, and that the indoor unit isn't just cycling on the back-up heat.
- If your outdoor heat pump is not running, please see: "Outdoor unit won't come on".
If not reaching temperature in the Cooling Mode, please see:
Please keep in mind that the information found on our website is provided free of charge and Hannabery HVAC does not assume any liability resulting from the information we provide. We hope this information helps, but please note that these are just rough guidelines, and not all possible situations are covered. Your HVAC system should be inspected and repaired by a trained technician.