HVAC Blog
When Your Heat Pump Stops Heating Below 30 Degrees: Is It Broken or Normal?
June 15, 2026 · 7 min read
Every January we get panic calls from heat pump owners who think their system died overnight when temps hit the teens. Most of the time it is working exactly as designed. If your installer did not explain this to you on day one, that's a problem with the installer, not the system. Here is how to tell what is actually happening.
The short version
Heat pumps work by pulling heat out of cold outdoor air and moving it inside. That sounds backwards but it is real physics, and it works very well in mild weather. When outdoor temps drop below about 30 degrees Fahrenheit, there is less heat in the outside air to grab, the system gets less efficient, and on most installs in OKC the auxiliary heat (electric strip or gas furnace) kicks in to help.
Air at the vents starts to feel cooler than it does with a straight gas furnace. The outdoor unit goes through a defrost cycle that looks alarming. Your electric bill goes up if the auxiliary heat is electric strip. None of that is the system breaking. It is the system doing what it was designed to do.
What is NOT normal is auxiliary heat running 24 hours a day in 45 degree weather, a heat pump that never gets the indoor temp anywhere near setpoint even with aux running, or a heat pump that makes loud grinding or popping sounds during defrost. Those are real problems.
The temperature thresholds you need to know
Heat pump efficiency drops on a curve as temperatures fall. The numbers here are approximate and depend on equipment, but they are accurate enough for OKC homeowners to use as mental anchors.
- Above 47 degrees: heat pump is at peak efficiency. COP (coefficient of performance) is roughly 3.5 to 4.0. That means for every 1 unit of electricity in, you get 3.5 to 4 units of heat out.
- 35 to 47 degrees: still very efficient. COP around 2.8 to 3.5. Auxiliary heat should not be running.
- 30 to 35 degrees: efficiency dropping noticeably. COP around 2.0 to 2.6. Some systems start to engage auxiliary heat for short stretches.
- 20 to 30 degrees: COP around 1.5 to 2.0. Auxiliary heat engages regularly. Air at the vents feels noticeably cooler. This is normal.
- Below 20 degrees: COP approaches 1.0 (the same as electric resistance heat). Auxiliary heat carries most of the load. This is also normal.
Why your air feels cool in cold weather (and why that is OK)
A gas furnace heats air to around 120 to 140 degrees at the vents. A heat pump in mild weather heats air to about 95 to 105 degrees. In cold weather (below 30 outside) that drops to 80 to 95 degrees at the vents.
80 to 95 degrees feels cooler than your skin (which is 92 to 98 degrees), so the air can feel almost cool when you stand in front of a vent. The room is still heating because the air is still warmer than the room and the system runs longer to compensate. But it is psychologically uncomfortable in a way a gas furnace is not.
We tell heat pump customers to expect this and not to panic. The thermostat will reach setpoint. It just takes longer in cold weather.
The defrost cycle: what it sounds like, why it happens
When the outdoor unit pulls heat out of cold air, frost forms on the outdoor coil. Every 30 to 90 minutes (depending on conditions) the system runs a defrost cycle: it reverses the refrigerant flow briefly so the outdoor coil heats up and melts the frost. While this happens, the auxiliary heat takes over indoors so you do not feel a temperature drop.
Defrost cycle symptoms that are normal: the outdoor unit makes a whoosh sound as the reversing valve switches, steam rises off the outdoor unit (this is just melted frost evaporating, not smoke), the unit may shut down for 5 to 15 minutes, and indoor temp may briefly feel slightly cooler if the auxiliary heat is slow to engage.
Defrost cycle symptoms that are NOT normal: loud grinding or popping (could be a failing reversing valve), the outdoor unit running but never shutting off (defrost cycle not completing), or visible ice persisting on the coil 30 minutes after a defrost cycle should have run.
3 signs your heat pump is actually broken (call us)
Most of the cold-weather concern we hear is not a real problem. These 3 specific symptoms are.
- Auxiliary heat running constantly in 35 to 50 degree weather. This means the heat pump itself is not contributing and the auxiliary is doing all the work. Common causes: refrigerant leak, failed reversing valve, or a controls problem. You will see this on your electric bill before you notice it any other way.
- Indoor temp drops below thermostat setpoint and stays there even with auxiliary heat running. Heat pump and auxiliary together should be able to maintain setpoint in any normal OK winter weather. If they cannot, something is undersized or failing.
- Outdoor unit fails to complete defrost cycles. Visible thick ice on the coil that has been there for over an hour, or the unit running continuously without the periodic whoosh of the defrost cycle, means the defrost control or the reversing valve has failed. This will eventually damage the compressor if not addressed.
If you are buying a new heat pump system in OK, ask these questions
A lot of heat pump installs in OKC have come from out-of-state installers or from companies that do not properly explain cold-weather behavior. The result is panicked customers in January. Before you sign on a new heat pump install, ask these specific questions.
- What is the heating load on my home, and what size heat pump are you sizing for? Sizing matters more on heat pumps than on straight AC.
- Am I getting strip heat backup or gas backup? In OKC, gas backup (dual fuel) is usually the better long-term choice if you have gas service. Strip heat is fine but more expensive to operate below 25 degrees.
- At what outdoor temperature does the auxiliary heat lock in to support? This should be programmed to a balance point that matches your home, not a default like 30 degrees universally.
- What is the operating cost estimate at 15 degrees outdoor? Real number, not a hand wave.
- What does the maintenance look like? Heat pumps need a couple of items checked twice a year (defrost cycle, reversing valve) that a straight AC does not.
Damaging admission: heat pumps are not always the right answer in OK
We install heat pumps. We service heat pumps. They are good equipment for a lot of OKC homes. But they are not the right answer for every home.
If you have working gas furnace under 12 years old and your AC dies, the right answer is usually to just replace the AC and keep the gas furnace. You do not need to convert to heat pump just because someone told you it was the modern thing to do. The math on doing that for the next 8 years rarely beats keeping the gas furnace.
If your home is large (over 3500 square feet) with high heating demand and an installer is recommending a single heat pump with strip backup only, push back. Either size up to a larger heat pump, add a gas furnace as dual fuel, or look at a different system architecture. Single heat pump with strip backup on a big OK home is going to deliver expensive January bills and uncomfortable cold-weather performance.
FAQ
- Why is my electric bill so high in January with a heat pump?
- Either auxiliary strip heat is running more than it should (which can mean a heat pump problem) or your home has higher heating demand than the original sizing accounted for (insulation, infiltration). January electric bills on heat pump only systems in OK with strip backup commonly run 200 to 400 dollars on a 2500 square foot home. If yours is higher, ask us to check.
- Should I switch from heat pump to gas furnace because of cold weather performance?
- Usually no, but the alternative is to add gas backup (dual fuel) if you do not already have it. Dual fuel gives you heat pump efficiency in mild weather and gas furnace efficiency in cold weather, with automatic switching. Conversion cost from electric strip backup to gas backup is usually 1800 to 4500 dollars depending on existing infrastructure.
- How much does emergency heat cost per hour to run?
- Electric strip emergency heat for a typical OK home runs roughly 2 to 4 dollars per hour at 2026 OG&E summer rates and 1.40 to 2.60 dollars per hour at winter rates. Run it during the rare emergency only, not as a default setting.
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Disclaimer
This post describes general heat pump behavior and is for educational purposes only. Specific performance depends on your equipment make and model, sizing, install quality, home efficiency, and local weather. Cost estimates reflect 2026 OG&E rates and OKC averages and are not binding quotes. Refrigerant handling is regulated by the EPA and should be performed only by certified technicians. Always have a licensed HVAC technician inspect your specific system before making repair or replacement decisions.
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