HVAC and Electrical Experts
Written by Peter
Master Electrician at PRO Electric plus HVAC, serving Fairfax, Loudoun, Arlington, and Prince William Counties. Virginia License #2705181607.
Auxiliary Heat Running All the Time Is Quietly Running Up Your Bill.
Heat pump repair across Fairfax, Loudoun, Arlington, and Prince William Counties.
Hi, I am Peter, the Master Electrician at PRO Electric plus HVAC. If you have a heat pump and you keep seeing the aux heat or emergency heat light on the thermostat, and your winter bill jumped, those two things are connected. Auxiliary heat is meant to help out now and then, not run as your main source of heat. When it runs constantly, something is making the heat pump fall behind, and it is worth finding out what. Let me walk through it.
Your heat pump heats the house efficiently by moving heat from the outside air indoors. The auxiliary heat is a backup set of electric strips that use a lot more power. They are supposed to step in only during very cold weather or a quick warm up, so if they are running all the time, the efficient part of your system is not keeping up.
Why auxiliary heat runs too much
- Very cold weather. Below a certain outdoor temperature, the heat pump cannot pull enough heat from the air on its own, and the aux strips are supposed to help. In a hard cold snap this is normal, and I cover the why in how heat pumps handle cold weather.
- A clogged air filter. Restricted airflow makes the heat pump struggle to deliver heat, so the thermostat calls for aux heat to make up the difference. This is one of the most common and cheapest fixes.
- The thermostat is set to emergency heat. If someone switched it to emergency or em heat, the heat pump is locked out and the expensive strips are doing all the work. That is a setting worth checking first.
- Low refrigerant or a dirty coil. If the heat pump has lost refrigerant or the outdoor coil is dirty or iced, it cannot make enough heat, and the aux strips run to cover the gap.
- Big thermostat jumps. Asking for a large temperature jump at once, such as from 62 to 72, often triggers aux heat. Smaller steps keep it on the efficient setting longer.
Check that you are not stuck in emergency heat
Before anything else, look at the thermostat. There is a real difference between auxiliary heat, which the system calls automatically, and emergency heat, which you turn on by hand and which locks out the efficient heat pump entirely. If it is set to emergency or em heat by mistake, you are paying top dollar to heat the house. I explain the difference in emergency heat versus auxiliary heat, and switching it back is often the whole fix.
Why it matters for your bill
Those electric strips can use several times the power the heat pump uses on its own, so when they run constantly, the cost adds up quickly. A little aux heat in a deep freeze is expected. Aux heat running in mild weather, or running for hours every day, is a sign the heat pump is not doing its share, whether that is airflow, refrigerant, a dirty or frozen outdoor unit, or a setting. Catching it keeps a comfortable house from turning into a painful bill.
How we help
We find out why the heat pump is leaning on its backup, whether that is a dirty filter, low refrigerant, a coil problem, a defrost issue, or a thermostat setting, and we get the efficient side carrying the load again. We handle heat pump repair across Northern Virginia.
Frequently asked questions
Why is my auxiliary heat always on?
Common reasons are very cold weather, a clogged air filter, the thermostat being set to emergency heat, low refrigerant or a dirty coil, or asking for a large temperature jump at once. In a hard cold snap some aux heat is normal, but running constantly in mild weather points to a problem worth checking.
Is it bad if my heat pump runs on auxiliary heat?
Occasional auxiliary heat in cold weather is normal and by design. Constant auxiliary heat is not, because the electric strips use much more power than the heat pump alone, so your bill climbs. If aux heat runs in mild weather or for hours daily, the heat pump is not keeping up and it should be looked at.
What is the difference between auxiliary and emergency heat?
Auxiliary heat is called automatically by the system to assist the heat pump when needed. Emergency heat is something you switch on by hand, and it locks out the heat pump so only the expensive electric strips run. Emergency heat is meant for when the heat pump has failed, not for everyday use.
Can a dirty filter cause auxiliary heat to run?
Yes. A clogged filter restricts airflow so the heat pump cannot deliver heat well, and the thermostat calls for auxiliary heat to make up the difference. Replacing the filter is the first and cheapest thing to try and often reduces how much aux heat runs.
Why did my electric bill spike in winter with a heat pump?
Most often because the auxiliary or emergency electric heat ran far more than it should. That can come from cold weather, a dirty filter, low refrigerant, a frozen outdoor unit, or the thermostat being left on emergency heat. Finding why the heat pump fell behind is how you bring the bill back down.
Aux heat running nonstop this winter?
Heat pump repair across Northern Virginia.