Symptom
Furnace blowing cold air?
A furnace blowing cold air is often a thermostat set to fan On rather than Auto, a furnace that has shut its burners off on a safety limit, or an ignition problem. With a heat pump, briefly cool air during a defrost cycle is normal. If the air stays cold with the thermostat set correctly, the system needs to be diagnosed.
Soon. Uncomfortable, and in a cold snap it can become urgent. For no heat at all on a cold night, call — emergency service runs 24/7.
What usually causes this.
These are the common possibilities, not a diagnosis. A page cannot tell which one it is — that takes a technician testing the system.
- Outdoor unit
- Thermostat
- Ducts & vents
- Filter & return
- Heat section
- Blower
- Fan set to On
- With the thermostat fan set to On, the blower runs between heating cycles and moves unheated air. Setting it to Auto usually fixes this.
- Warm-up delay
- Many furnaces start the blower a moment after the burners light. A few seconds of cool air at start-up is normal.
- Burners shut off by a safety limit
- A clogged filter or blocked return makes the furnace overheat. The limit switch turns the burners off while the blower keeps running, so air turns cold.
- Ignition or flame-sensor fault
- If the burners fail to light or drop out, the blower may still run and push cold air.
- Heat pump defrost or low charge
- Heat pumps briefly blow cooler air during defrost. Air that stays lukewarm can mean a low refrigerant charge or a reversing valve problem.
- Leaking ducts
- Ducts leaking in a cold attic or crawlspace can deliver air noticeably cooler than it left the furnace.
What you can safely check.
- Set the thermostat fan to Auto and the mode to Heat.
- Replace a dirty filter.
- Check that return grilles aren't blocked.
- For a heat pump, watch the outdoor unit: steam and a few minutes of cooler air during defrost are normal.
Leave these alone
- The burners, gas valve, flame sensor and igniter.
- Resetting the furnace repeatedly to get it to light.
Call rather than book online if:
- You smell gas — leave the house and call the gas utility or 911 from outside
- A carbon monoxide alarm sounds
- There's no heat and temperatures are dropping below freezing
What we check when we get there.
In order, and every time — the point of a diagnostic is to find out which cause it is before anything is replaced.
- 01The technician confirms the thermostat call, then watches a full heating cycle to see whether the burners light and stay lit, or whether a limit or flame-sensing fault is shutting them down.
- 02For heat pumps, pressures, reversing valve operation and defrost behavior are checked.
What it is likely to cost.
A thermostat setting costs nothing. Flame sensors and igniters are moderate repairs; blower motors and reversing valves cost more. You get the price before work starts.
- Heating diagnostic
- $89
- Flame sensor
- From $149
- Ignitor
- From $199
- Blower motor
- From $499
- Reversing valve
- From $699
Prices are starting points for standard work in the Savannah area. Final price depends on the system and site, and is confirmed before work begins. Permits and code-required upgrades may be additional.
Questions people ask about this.
- Is it normal for a heat pump to blow cool air in winter?
- Briefly, yes. During defrost the system reverses for a few minutes to clear frost off the outdoor coil. Air that stays lukewarm for long periods isn't normal.
- The furnace blows warm air, then cold, then warm again.
- That pattern often means the furnace is overheating and tripping its limit switch — frequently because of a clogged filter or restricted airflow. Replace the filter; if it continues, have it checked.
Work out the decision:Seasonal Checklist
Further reading:Getting a furnace ready for its first cold night
The service that fixes it.
Heating & Furnace Repair is the work behind this symptom. Its page covers what is involved, how it is quoted and what we stand behind.
Symptoms that sit next to it.
Systems rarely fail in one way only. If one of these is also true, say so when you book — it narrows the diagnosis before anyone arrives.
Furnace or heat pump not heating, blowing cold air, cycling or running up the bill.
- Furnace won't turn on or lightA gas furnace that won't light is most often a worn igniter, a dirty flame sensor, a clogged filter tripping a safety limit, or a thermostat or power problem.
- Furnace turning on and offA furnace that runs for a few minutes, shuts off and restarts over and over is short cycling.
- Heat pump not heatingA heat pump that runs but doesn't heat well may have a thermostat set incorrectly, a dirty filter, an iced-up outdoor coil, a low refrigerant charge, or a reversing valve or defrost problem.
- Heat pump iced up or stuck in defrostIn cold, damp weather a heat pump's outdoor coil collects frost, and the system runs a defrost cycle to melt it — steam and a few minutes of cooler indoor air are normal.
- Aux heat always on / high winter billAuxiliary heat is the backup — usually electric resistance — that helps a heat pump in very cold weather or during defrost.
Not sure which it is?Describe it to the assistant
Everything else we are called about.
The whole index, in three groups.
HUMIDITY, AIRFLOW & ENERGY BILLS
House feels humid or dampSome rooms too hot or coldPower bill suddenly higher
Get it looked at.
We cover Savannah, the Coastal Empire and the South Carolina Lowcountry. Tell us what the system is doing — you do not need to know the cause. The diagnostic price is given to you before the visit, and the repair price before any work starts.
No heat, or no cooling at all?Call rather than send a request — (912) 858-3737 is answered around the clock.