Heat Pump Not Heating? Normal vs Broken, Sorted
By the HVAC Responder Editorial Team
Half of "broken" heat pumps are performing normally: supply air at 85–105°F feels cool to a hand expecting furnace heat, light frost in damp cold is routine, and the periodic whoosh-and-steam-cloud is the defrost cycle doing its job. The genuine failure signs are different: a house that cannot hold setpoint, an outdoor unit encased in solid ice through multiple defrost cycles, backup heat running constantly in mild weather, or an outdoor fan that never spins.
Normal things that look broken
Mild-feeling supply air is the physics of moving heat rather than making it. Frost on the coil in 30–45°F damp weather is expected, and the unit clears it by briefly reversing into cooling mode — fan stops, steam rises, something whooshes. Five minutes later it is heating again. None of this needs a service call, and knowing it saves the after-hours fee.
Broken things that look subtle
A solid ice shell that survives defrost cycles means defrost controls, sensors, or charge have failed — and fan blades striking ice will destroy them. Auxiliary heat running in mild weather (check for an AUX indicator glowing constantly) means the changeover logic or the heat pump itself is failing, and the electric bill is absorbing the evidence. A dead outdoor fan with a humming unit is the same capacitor story as an AC.
The thermostat is a frequent villain
Heat pump thermostats are configuration-sensitive: wrong equipment settings run backup heat as primary, and aggressive setback schedules trigger expensive aux recovery every morning. If bills spiked after a thermostat change, the thermostat is suspect number one. Modest setbacks (2–3°F) or none at all suit heat pumps better than deep nightly dips.
The wider failure picture for heat pump services
This guide covers one symptom cluster. The same equipment produces a family of related complaints, and knowing the neighbors helps you describe yours precisely on the phone:
Considering replacing both furnace and AC at once
One heat pump can replace both — this is exactly the moment the heat-pump math is strongest.
Existing heat pump ices over and stays iced
Normal defrost handles light frost; an ice ball means defrost controls, sensors, or charge need service.
Electric bills spike in winter
Auxiliary resistance heat running more than it should — controls, balance point, or capacity problem.
All-electric home heated by baseboards or an electric furnace
A heat pump typically delivers the same heat for a half to a third of the electricity.
Chasing utility rebates or the federal credit
Heat pumps carry the largest residential HVAC incentives available — the biggest federal credit in the category plus local stacking.
If the checks point to a pro: how the call unfolds
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Describe the project, not just the equipment
Age of the current system, rooms that never worked right, fuel type, timeline. Replacement is a design job, and context shapes the quote quality.
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Matched to an installer, not a salesman
Your call routes to an independent local company that installs your equipment type week in, week out — and can show licenses and insurance without being chased.
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Load calculation before price
A legitimate replacement quote follows a Manual J load calculation and a duct check. Model numbers, scope, permits, and commissioning steps go in writing.
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Compare bids like a buyer
No obligation and no exclusivity — take the quote, set it against any competitor, and award the job to whoever earns it on scope, not just price.
Timing matters here too: this is planned-work territory, and planned work quoted in shoulder season — spring and fall, when contractor calendars have room — consistently draws sharper bids than the same request made mid-rush.
What separates a good install from an expensive one
The equipment brand matters less than the installation decisions around it: a load calculation instead of a driveway guess, ducts measured for the airflow the new system actually needs, refrigerant charge and airflow verified with instruments at commissioning, and the permit pulled rather than skipped. Two crews installing the identical unit can deliver measurably different efficiency for its entire fifteen-year life.
Read competing bids by scope, not bottom line. Model numbers for every component, line-set and drain handling, electrical work, permit responsibility, commissioning steps, and the labor warranty — in writing. The cheapest bid is usually cheapest because something on that list is missing, and the missing item is rarely missing by accident.
Deeper heat pump services questions
Do heat pumps actually work in cold climates?
Modern cold-climate models hold most of their rated capacity at 5°F and keep producing useful heat below -10°F — the Maine and Minnesota markets run on them. The engineering requirements are real, though: proper sizing to the heating load (not the cooling load), a correctly set balance point, and adequate backup for the coldest tail of the year. The technology stopped being the limitation a decade ago; installation quality is the limitation now.
Why is there ice on my heat pump — and when is it a problem?
Light frost on the outdoor coil in cold, damp weather is normal, and the unit periodically reverses into defrost to clear it (steam and a whooshing sound — also normal). A solid ice shell, ice that persists through defrost cycles, or fan blades striking ice are service calls: typically defrost controls, a bad sensor, low charge, or blocked drainage under the unit.
What does a heat pump cost to run versus a gas furnace?
It hinges on local rates. A heat pump moving 3 units of heat per unit of electricity competes with gas whenever electricity costs less than about 3–4× gas per unit of energy. At typical national averages the heat pump wins in mild and moderate climates and roughly ties in cold ones — where dual-fuel setups capture the best of both. Your utility’s actual rates decide it, not national averages.
Can a heat pump reuse my existing ductwork?
Usually, with a caveat: heat pumps move more air at lower temperatures than furnaces, so ducts sized for a furnace sometimes run high static pressure with a heat pump — noise, weak rooms, and efficiency loss. A competent installer measures static pressure and either confirms the ducts or scopes the fixes. Skipping that measurement is how "my new heat pump is loud and the back room is cold" happens.
What incentives apply to heat pumps right now?
The federal 25C credit: 30% of installed cost up to the category’s largest annual cap, for qualifying models. Many states and utilities stack rebates from a few hundred dollars to several thousand on top, especially where gas-to-electric conversion is policy. Check dsireusa.org and your utility, and get the model’s qualification status in writing from the contractor before signing.
Terms you'll hear during this diagnosis
Heat Pump — A heat pump is a refrigerant-based system that moves heat rather than generating it: out of the house in summer (exactly like an air conditioner) and into the house in winter, by extracting heat from outdoor air even when that air is cold. Because moving heat takes far less energy than creating it, a heat pump typically delivers two to four units of heat per unit of electricity consumed.
The winter trick is the reversing valve, which flips the refrigerant flow so the outdoor coil absorbs heat and the indoor coil releases it. Modern cold-climate models hold useful capacity below 0°F. Most homes pair the heat pump with backup heat — electric strips or a gas furnace ("dual fuel") — for the coldest tail of the year. Nearly every ductless mini-split is a heat pump too.
Balance Point — A heat pump’s balance point is the outdoor temperature at which its heating output exactly equals the house’s heat loss. Above it, the heat pump carries the load alone; below it, backup heat — electric strips or a furnace — must make up the difference. Typical balance points fall between 25 and 40°F depending on equipment capacity and the house envelope.
This is the setting that quietly decides winter bills on heat pump systems. Configured lazily, auxiliary heat runs during mild weather at triple the cost per BTU; configured well, expensive backup runs only when physics requires it. Insulation upgrades lower the balance point for free, and cold-climate equipment pushes it far down the thermometer. Ask, at commissioning, what yours is set to — and why.
HSPF2 — HSPF2 (Heating Seasonal Performance Factor 2) rates a heat pump’s heating efficiency: seasonal heat output in BTUs divided by watt-hours of electricity consumed, under the test conditions in force since 2023. The federal minimum is 7.5 HSPF2; efficient units score 8.5 or higher. Higher numbers mean more heat per kilowatt-hour, which directly sets winter operating cost.
HSPF2 is the winter sibling of SEER2 — one machine, two ratings. For cold climates the rating to interrogate is capacity retention at low temperature (output at 5°F), which HSPF2 summarizes only loosely; two units with equal HSPF2 can behave very differently at zero degrees. Cold-climate certified models publish those low-temperature tables — ask for them.
SEER2 — SEER2 (Seasonal Energy Efficiency Ratio 2) is the federal efficiency metric for air conditioners and heat pumps in cooling mode, in force since 2023. It measures seasonal cooling output divided by electricity consumed, tested under more realistic external duct pressure than the old SEER standard — which is why SEER2 numbers run about 4.5% lower than equivalent SEER ratings.
Federal minimums sit at 13.4 SEER2 in northern states and 14.3 in the South and Southwest. Mid-efficiency equipment lands at 15–17 SEER2, and premium variable-speed systems reach 20+. The economics: each SEER2 point trims roughly 5–7% off cooling energy, so high ratings pay back fastest in long cooling seasons. Past ~18, you are buying comfort features as much as efficiency.
When to stop troubleshooting and call
- The house loses ground against the setpoint in weather the system used to handle.
- Ice persists or thickens through defrost cycles.
- AUX/emergency heat runs in weather above ~40°F.
- The outdoor unit trips breakers or the fan stops spinning.
Ready for a pro?
One call routes you to an independent local contractor for heat pump service — fee quoted up front.
Call (800) 555-0100Related questions
Should I switch to Emergency Heat when it gets really cold?
No — emergency heat is for actual heat pump failure, not cold weather. It abandons the efficient machine entirely for resistance strips at triple the cost. A properly configured system already blends backup heat automatically as temperatures fall; the manual switch is for the day the outdoor unit is genuinely dead.
Why is there a puddle of water under my heat pump in winter?
Defrost meltwater — normal, and the reason units sit on raised pads. It becomes a problem when it refreezes into a growing ice base that reaches the coil or fan; keep the drainage path clear and the unit elevated above ice level.