Furnace Takes Too Long to Heat Home in Greater Vancouver

A furnace that runs for hours but never gets the home to the set temperature — or takes much longer than it used to — is losing capacity somewhere in the system.

What This Symptom Means

Long heat-up times mean the furnace is delivering less heat than the home is losing to the outdoors. The gap could be on the equipment side (reduced output) or the building side (increased heat loss). Most commonly, it is a combination.

Common Causes

• Clogged filter reducing heat output
• Dirty heat exchanger reducing heat transfer efficiency
• Duct leakage losing conditioned air before it reaches living spaces
• Home heat loss increase — failed window seals, new air gaps, or unsealed renovation penetrations
• Furnace running at reduced output due to component wear
• Very cold outdoor temperature — demand exceeds what the system was sized for
• Furnace undersized for additions or recent insulation removal

What Homeowners Can Check Safely

• Replace air filter
• Check for obvious drafts — candle or incense stick near window frames and door edges reveals air infiltration
• Verify all registers are open

When to Call a Licensed Technician

Some furnace issues require a licensed HVAC technician. Do not attempt to open gas lines, replace internal components, or reset persistent lockouts without professional diagnosis.

• Combustion efficiency test
• Duct leakage test
• Building envelope assessment for air sealing opportunities
• Heat load calculation to confirm system sizing adequacy

Frequently Asked Questions

My furnace used to heat the house in 20 minutes. Now it takes over an hour. Why?

If the home and thermostat settings are the same, the most likely causes are: dirty filter or heat exchanger reducing output, duct leakage that has worsened, building envelope degradation increasing heat loss, or age-related efficiency decline in the furnace. An annual tune-up that includes combustion analysis would identify the equipment side of this.

Can duct cleaning help my furnace heat faster?

Duct cleaning itself does not typically improve heating speed unless the ducts have significant debris blockage. However, duct sealing — addressing gaps that leak heated air into unconditioned spaces — can meaningfully improve how quickly conditioned air reaches living areas.

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