| Square Footage | Furnace BTU |
|---|---|
| 1,000-1,200 sq. ft. Home | 40,000 - 60,000 BTU |
| 1,200-1,500 sq. ft. Home | 60,000 BTU |
| 1,500-1,800 sq. ft. Home | 60,000 - 80,000 BTU |
| 1,800-2,500 sq. ft. Home | 80,000 - 100,000 BTU |
| 2,500-3,500 sq. ft. Home | 100,000 to 120,000 BTU |
Let’s face it—you probably don’t think about your furnace until it stops working. And when that happens, it’s usually during a freezing Canadian winter, right when you need it the most.
But don’t panic! Many furnace problems can be fixed easily without calling a professional. All you need is a little knowledge, a careful approach, and this handy guide.
We’ll walk through the 22 most common furnace problems, what might be causing them, and how to fix them—or when it’s better to call a certified HVAC technician.
If the blower is running but no warm air is coming out, it could be:
🔧 Fix It:
Check thermostat settings. Set the mode to “heat” and fan to “auto”. Then verify gas supply is active and, if applicable, relight the pilot. Still nothing? Time to get expert help.
Tired of your basement freezing while your upstairs feels like a sauna?
Causes:
🔧 Fix It:
Open all vents, replace filters, and check for airflow blockages. If you suspect duct issues, consider professional duct sealing or inspection.
Banging, clicking, hissing, or buzzing? These can signal:
🔧 Fix It:
Turn off the unit and check screws, filter, and flame color. If it’s scraping or thumping, shut it down and call a pro.
This is called short cycling, and it’s bad for your furnace’s health.
Common causes:
🔧 Fix It:
Change the filter, test thermostat batteries, and ensure airflow isn’t blocked. If it persists, schedule a system check to avoid long-term damage.
Clicking but not firing? No flame? That’s likely due to:
🔧 Fix It:
Replace thermostat batteries, clean the igniter carefully, and ensure the gas line is open. If ignition still fails, don’t DIY—it’s a safety risk.
If your furnace isn’t pushing air, it could be:
🔧 Fix It:
Reset breakers, change the filter, and inspect belts. If there’s no power to the blower motor, call an HVAC tech.
Symptoms include:
🔧 Fix It:
Change batteries, clean the inside, and ensure it’s not near a heat source. Consider upgrading to a smart thermostat for more accurate control.
Dirty filters = low airflow = high energy bills.
🔧 Fix It:
Replace filters every 1–2 months in winter. If reusable, vacuum + wash it gently and let it dry before reinserting.
📖 Related: How to Replace a Furnace Filter
Standing water near your furnace? Your condensate drain line may be blocked.
🔧 Fix It:
Vacuum the line, flush it with vinegar, or clear it with a flexible brush. If leaks continue, check for cracked tubing or faulty pumps.
Could be:
🔧 Fix It:
Relight using the manual’s instructions. If it won’t stay lit or burns yellow/orange, shut down the system and call a licensed tech.
A bad limit switch can shut your furnace down for safety, especially if it’s overheating.
🔧 Fix It:
Turn off power and test it with a multimeter. If you’re not sure, leave this one to the pros.
This is extremely serious.
Signs:
🚨 Emergency:
Evacuate immediately. Call 911. Install CO detectors near the furnace and bedrooms. Don’t wait!
The thermocouple is a small safety device that shuts off gas if the flame isn’t burning.
🔧 Fix It:
Use a multimeter to test output (should be 25–30 mV). If below, replace it. Clean any corrosion on the tip.
Modern furnaces often use electronic igniters which can fail due to:
🔧 Fix It:
Call a pro to match correct voltage and replace if needed.
Leaky or blocked ducts reduce airflow and comfort.
🔧 Fix It:
Inspect visible ducts and seal joints with UL 181 metal foil tape. Avoid cloth duct tape. Consider duct inspection services for older homes.
Main culprits:
🔧 Fix It:
Check for visible leaks and clean drainage areas. Replace faulty pump if necessary.
No sound, no lights?
Check:
Still nothing? Call a technician.
🔧 Fix It:
Set fan to AUTO, check pilot, and change filters. If the air is still cold, your system may be overheating or misfiring.
Types:
🔧 Fix It:
Turn off furnace, clean filters, and inspect ducts. Call a pro if smell persists.
📖 Read more: Burning Smell from Furnace – Causes & Fixes
If stuck open, furnace won’t fire up. Could be:
🔧 Fix It:
Clear vents, inspect the motor. Replace switch if needed (or call a tech).
🔧 Fix It:
Switch to AUTO mode. Replace faulty parts if necessary.
This usually points to:
🔧 Fix It:
Replace filter, test thermostat, and check airflow. Still happening? Call a pro for diagnostics.
Call an HVAC tech if:
🔧 Pro Tip: Book an annual tune-up before winter hits.
Furnace acting up? Don’t sweat. With this guide, you now have the knowledge to handle the most common issues confidently. And remember, when in doubt—play it safe and call a trusted HVAC pro.
🏡 Keep your home warm, safe, and comfortable all winter long.
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