There is a specific kind of confusion that happens when you walk past a heat vent, feel air blowing, and realize… it’s cold. Your furnace is running. The fan is spinning. But instead of a cozy blast of warmth, you’re getting a chilly breeze that feels like someone left the front door open.
For homeowners in Calgary, where heating is a survival necessity for 8 months of the year, this is a frustrating problem. The good news? It doesn’t always mean your furnace is broken.
Before you pick up the phone to call Shift Heating & Cooling for a furnace repair, there are several checks you can do yourself. You might just save yourself a service call fee! However, if these tips don’t work, our team is ready to dive into the complex mechanical issues that require a professional touch.
Here is our comprehensive troubleshooting guide for when your furnace blows cold.
1. Check Your Thermostat Settings (The “Fan” vs. “Auto” Mistake)
It sounds simple, but this is the #1 reason we get called out for “cold air” issues.
Check your thermostat. Is the fan setting switched to “ON” instead of “AUTO”?
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AUTO: The fan only runs when the furnace is actually heating the air. This is what you want.
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ON: The fan runs 24/7, constantly circulating air. When the burners turn off, the fan keeps spinning, circulating room-temperature air that feels cold against your skin (the wind chill effect).
** The Fix:** Switch it back to “AUTO.” If the air warms up within a few minutes, problem solved!
2. The Dirty Filter Disconnect
In Calgary, our air is dusty and dry. Furnace filters here get clogged faster than in many other cities. A completely blocked filter restricts airflow so much that the furnace overheats.
When the internal temperature gets too high, a safety switch called the Limit Switch trips. This shuts off the burners to prevent a fire, but the blower fan stays on to cool the unit down. The result? Your furnace blows cold air.
The Fix: Pull out your filter. If it looks like a grey carpet of dust, replace it immediately. Turn the furnace off at the breaker for 5 minutes to reset the switch, then turn it back on. If heat returns, be sure to change your filter every 1–3 months.
3. Check Your Intake Vents for Snow
This is a uniquely “Calgary” problem. If you have a high-efficiency furnace (which most newer homes in Calgary do), you likely have two white plastic PVC pipes sticking out of the side of your house. One is for exhaust, and one is for fresh air intake.
After a heavy snowfall or a blizzard with drifting snow, these pipes can get buried. If the fresh air intake is blocked by snow or ice, the furnace “suffocates” and shuts down the burners for safety.
The Fix: Bundle up, go outside, and check the pipes. Clear away any snow drifts, ice, or leaves blocking the openings. Note: Be gentle—don’t crack the PVC pipes in the cold.
4. The Pilot Light (For Older Furnaces)
If your home in an older Calgary neighbourhood still has a mid-efficiency furnace (usually built before 2010), you might have a standing pilot light. If a draft blew it out, the burners won’t ignite.
The Fix: Check the instructions on your furnace panel. If you feel comfortable, try relighting it. If it lights but goes out again immediately, you likely have a faulty thermocouple, which requires a professional furnace repair.
5. When to Call Shift Heating & Cooling
If you have checked the thermostat, replaced the filter, cleared the vents, and you still have cold air, the issue is mechanical. Common culprits include:
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Faulty Flame Sensor: Over time, soot builds up on the sensor that detects if the gas is burning. If it’s dirty, it shuts the gas off as a safety precaution.
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Broken Ignitor: If the ignitor is cracked, the gas never lights.
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Gas Valve Failure: The valve may be stuck closed, preventing fuel from reaching the burners.
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Ductwork Leaks: If you have massive tears in your ducts (perhaps in an unheated crawlspace), cold air from the basement could be getting sucked into the system.
Why Choose Shift Heating & Cooling?
Diagnosing these internal components requires a multimeter and gas-fitting certification. Attempting to DIY repairs inside the cabinet can be dangerous and may void your warranty.
At Shift Heating & Cooling, our technicians carry the diagnostic tools to pinpoint the exact cause of the “cold blow” within minutes. We service all major brands found in Calgary homes. Plus, with our transparent pricing, we’ll tell you exactly what the part costs—whether it’s a $50 sensor or a $400 control board—before we proceed.
Conclusion
A furnace blowing cold air is your home’s way of asking for help. Sometimes it’s just asking for a new filter, but other times it’s a cry for professional repair.
Don’t settle for wearing a parka in your living room. If you’ve tried these troubleshooting steps and the chill remains, contact Shift Heating & Cooling. We provide fast, reliable furnace repair in Calgary to turn that cold breeze back into the cozy warmth you deserve.