Furnace Blowing Cold Air Instead of Heat in Calgary
Cold air from the vents has a few causes you can check safely, and Carrier names the most common one: the thermostat fan set to On instead of Auto. If you smell gas, leave first and call 911 from outside.
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A local furnace technician will call you back as soon as possible. If this can't wait, call other furnace technicians too.
What to do right now
Smell gas or hear a CO alarm? Leave, don't troubleshoot
Skip every step below. Get everyone outside, then call 911, and ATCO at 1-800-511-3447 for a gas smell.
Set the thermostat to Heat and the fan to Auto
Check it isn't on Cool. With the fan on On, the blower runs all the time, heat or no heat. On Auto it runs with the heat.
Give it a few minutes
Carrier says some furnaces hold the blower for about 30 to 60 seconds after the burners light.
Check the filter
A clogged filter can make the furnace overheat. A safety switch then shuts the burners off while the fan keeps going. Switch the furnace off before you change the filter.
Open the registers and clear the returns
Supply vents should be open. Return grilles shouldn't be covered by furniture or rugs.
Look at the pipes outside
ATCO's no-heat list includes making sure the intake and exhaust pipes are free of snow and ice. Clear loose snow by hand, and leave ice on the pipe alone.
If your CO alarm sounded, stay out of the house and call 911 instead. Get the furnace checked by a professional even if it heats again afterwards.
Are other gas appliances out too?
If the stove or water heater has also stopped, the gas supply may be off. Call ATCO's emergency line, 1-800-511-3447. Don't relight anything yourself; ATCO asks you to wait for instructions from its technician.
Stop there
The flame sensor, limit switch, gas valve and igniter are jobs for a qualified technician, Carrier says.
No heat from furnace: what is happening
The blower and the burners do separate jobs. The fan can run while the burners are off, or after they light and shut down again, and then the air comes out cold.
Carrier's list of causes runs from the thermostat fan setting, to a dirty filter tripping the high-limit switch, to parts only a technician should touch.
Furnace not heating house: when it's an emergency
- Gas smell or a CO alarm: get out, then call 911 from outside.
- A baby, an older person or someone unwell is getting cold: don't wait for a call back. Go somewhere warm, or call 911 if anyone is in danger.
In January, Calgary's normal overnight low is about -13 C (Environment Canada, 1981 to 2010 normals). In the January 2024 cold snap, the low at Calgary International reached -36.2 C.
If you run an electric space heater, plug it directly into the wall, not into an extension cord. Give it clear space, well away from bedding, curtains and anything that can burn.
Furnace blower on but no heat: what a professional checks
Past the thermostat, filter, vents and outside pipes, Carrier puts the flame sensor, limit switch, gas valve and igniter on the technician's side of the line. Carrier also calls the igniter delicate and high-voltage. Keep the furnace panels on.
Questions
Is a furnace blowing cold air dangerous?
Cold air alone means the house isn't being heated. It turns dangerous with a gas smell or a CO alarm: get out, then call 911 from outside.
It also matters quickly when someone at home is a baby, older or unwell. Don't wait for a call back. Go somewhere warm, or call 911 if anyone is in danger.
Is it normal for a furnace to blow cold air at first?
Carrier says some furnaces wait about 30 to 60 seconds after the burners light before the blower starts, so give it a few minutes. If the air is still cold after that, work through the checks above, starting with the fan setting.
My furnace is blowing cold air and smells like gas. What do I do?
Get everyone out of the building now. Leave lights and appliances alone on the way out. Once you're outside, call 911. For a gas smell, also call ATCO's gas emergency line: 1-800-511-3447. Don't go back inside until the fire department says it's safe, or a professional has fixed the problem.
Why is there no heat from my furnace?
Go through it in this order. The thermostat may be on Cool, or the fan on On. A dirty filter may have tripped the high-limit switch. Vents may be closed or blocked. ATCO adds two more: power to the furnace, and the outside pipes.
If every gas appliance is out, call ATCO's emergency line. Beyond that, a professional checks the flame sensor, limit switch, gas valve and igniter.
Sources
- Carrier: Furnace blowing cold air
- Carrier Canada: Furnace not kicking on
- Carrier: Furnace short cycling
- Carrier: Furnace ignitor
- ATCO Gas: Report a gas emergency (and no-heat checklist)
- Environment and Climate Change Canada: Calgary climate normals 1981-2010
- Environment and Climate Change Canada: Calgary daily data, January 2024
- Technical Safety BC: Space heater safety guide
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