Furnace Blowing Cold Air? 3 Checks First, Fixes $133 to $505

Installed prices for parts and labor: HomeAdvisor (Jun 2026) and HomeGuide (Aug 2025). HomeAdvisor's average furnace repair is $318.

Do this now: furnace blowing cold air

Start with safety, then work through the checks that do not involve opening the gas side of the furnace.

1. Smell gas? Leave now. Do not touch light switches, the thermostat or appliance controls. From outside, call 911 and the gas utility (Southwest Gas).
2. CO alarm sounding? Do not look for the source. Get everyone outside, call 911, and stay out until responders say it is safe (CPSC).
3. Thermostat: set it to HEAT, above room temperature, and set the fan to AUTO. Carrier calls a fan left on ON the most common cause of cold air. Replace the batteries (Lennox).
4. Filter: if it is gray and clogged, replace it. Carrier says to change basic filters every 1 to 3 months.
5. Power: check the breaker and the furnace's power switch. Bryant says not to keep resetting a breaker that trips again.
6. Fuel: check that other gas appliances work, or that the oil or propane tank is not empty (Carrier, Lennox).
7. Protect the pipes while you wait. Open kitchen and bathroom sink cabinet doors and let cold water drip from faucets on exposed pipes (American Red Cross). Keep space heaters at least 3 feet from drapes, furniture and bedding, and never heat the house with the stove, a grill or a generator (CDC).

Is it an emergency? When cold air means call today

Cold air from a furnace is an emergency when it comes with a gas smell, a CO alarm, soot around the furnace, or a house that is dropping toward freezing. Otherwise, run through the checks and book a normal visit if they do not fix it.

• Soot around the furnace: Carrier says to turn off the system and call a professional.
• Yellow flame instead of blue: Lennox says it suggests a blockage.
• Breaker trips again: leave it off and call (Bryant).
• House getting cold: the Red Cross says to keep heat no lower than 55 F when away, because pipes can freeze. The CDC says a body temperature below 95 F is an emergency; get medical help.

HomeGuide puts emergency or after-hours furnace labor at $140 to $210 an hour, against $75 to $150 during normal hours. See emergency HVAC repair for a night or weekend breakdown, and gas leak if you smell gas.

Why is my furnace blowing cold air? The common causes

Most furnaces that blow cold air have a thermostat problem, an airflow problem, or a burner that will not light or stay lit, according to Carrier, Lennox and Bryant. Here is how each one happens.

Thermostat set wrong

A fan set to ON runs the blower all the time, so it pushes room-temperature air between heating cycles. Carrier calls this the most common cause; set it to AUTO so the blower runs only while the furnace heats. Lennox says low batteries can make a battery-powered thermostat misbehave.

Dirty filter and the high-limit switch

A clogged filter starves the furnace of air until it overheats, and the high-limit switch shuts off the burners while the blower keeps running, which feels like cold air (Bryant, Carrier). A new filter often fixes it. If the switch itself has failed, HomeAdvisor puts a relay or high-limit switch at $150 to $300.

Pilot light or igniter

Lennox says most furnaces made since 2010 have no pilot light; they use an electronic igniter. On older furnaces, Carrier says relighting a pilot by the instructions on the unit is a homeowner task, while pilot assembly repairs are for a professional. Lennox says a pilot that keeps going out can point to a faulty thermocouple, which needs a technician, or to the gas valve. Never relight a pilot if you smell gas.

Flame sensor

A dirty flame sensor fails to detect the flame, so the furnace shuts off the burners as a precaution, says Carrier. Bryant and Lennox both recommend leaving the sensor to a professional. HomeGuide puts the repair at $80 to $250.

Condensate line on a high-efficiency furnace

High-efficiency gas furnaces drain water through a plastic line, and Lennox says a blockage in those lines can shut down the burners and make the furnace blow cold air. Lennox says to make sure the PVC pipe that runs to the floor drain is clear. Carrier says malfunctioning condensate lines need a professional.

Gas supply, ducts and the control board

A furnace shuts off without enough gas, and a gas line problem can knock out the water heater or stove too (Lennox). Leaky ducts can pull in cold air, and closed vents or blocked returns cut airflow (Carrier, Lennox). A failing control board can run the blower without firing the burner (Lennox). Carrier says to note any blinking light code on the board and report it, not to repair the board yourself.

Why is my heat blowing cold air from a heat pump?

A heat pump's air feels cooler than a furnace's because it is: Carrier says heat pump supply air is typically 85 to 100 degrees F, against 120 to 140 degrees from a gas furnace. During a defrost cycle it can blow cool air for a few minutes; Trane says its cycles usually last 3 to 5 minutes, and Carrier says about 5 to 10. Trane says steam from the outdoor unit and a stopped outdoor fan are normal during defrost. Cold air all the time is not normal. See heat pump repair for ice, defrost and refrigerant problems.

What is safe to check yourself

The thermostat, batteries, filter, breaker, vents and the condensate drain pipe are safe for a homeowner to check. Leave the rest alone:

• Safe: thermostat mode and fan setting, batteries, filter, breaker and furnace switch, open supply vents and clear returns, the PVC condensate pipe, relighting a standing pilot by the label instructions when there is no gas smell.
• Leave to a technician: gas valves, burners, the flame sensor, the control board and any blinking code. Carrier says to open the cabinet only if your owner's manual allows it, and that DIY work on gas components can lead to safety hazards. CPSC says never to service fuel-burning appliances without the knowledge, skill and tools.

How much does it cost to fix a furnace blowing cold air

Fixing a furnace that blows cold air costs $133 to $505 for most repairs in HomeAdvisor's 2026 data, with a $318 average. HomeGuide puts the average repair at $125 to $480 and labor at $75 to $150 an hour. A thermostat setting or a filter costs little or nothing; a limit switch, igniter or flame sensor sits in the low hundreds; a gas valve or control board can reach $600 to $800. Full part prices are in furnace repair costs.

Furnace repair near me: what to ask

• What is the service call fee, and does it count toward the repair?
• What failed, and can I see it? Ask for the part and labor as separate lines.
• Is the part under warranty? Ask before you pay for a board or valve.
• How old is the furnace? If it is over 15 years, ask for a replacement price too. How long a furnace lasts explains the repair or replace rules.
• License: ask for the license number and proof of insurance. The HVAC license table lists who issues licenses in six states.

More heating guides are on the HVAC repair hub, and prices for every trade are in home repair costs. Calls go to an independent company that serves your area and takes this kind of job. How calls work.