When the furnace runs but some rooms stay cold, the cause is usually airflow: a clogged filter, closed or blocked vents, a blocked return grille or a loose duct. Check those first. If every room is cool, or the furnace keeps shutting off, it’s more likely the furnace itself.
Free Checks First
- Replace the filter if it’s grey or packed with dust.
- Open the supply vents in the cold rooms and move furniture, rugs and curtains off them.
- Clear the return grilles (the big ones that pull air back to the furnace). A blocked return starves the whole system.
- Close doors less: a room with a supply vent and no return often needs the door open or a gap under it.
- Check the thermostat isn’t next to a heat source that makes it shut off early.
Common Patterns
| Pattern | Usual cause |
|---|---|
| Upstairs hot, basement cold | Heat rises. Partly closing upper vents and opening lower ones often helps. |
| Basement suite cold, main floor fine | One furnace heating two spaces, with few vents or a closed damper to the suite |
| One room always cold | A long duct run, a disconnected or crushed duct, or an outside wall with poor insulation |
| Every room cool, furnace runs a lot | A clogged filter, weak blower or the furnace not reaching full heat |
| Rooms warm, then cold, then warm | Short cycling. See furnace short cycling. |
Basement Suites
Many Metro Vancouver houses have a basement suite on the same furnace as the main floor. The suite usually has fewer vents, and the thermostat is upstairs, so the furnace stops when the main floor is warm. Tell David where the thermostat is and which part of the house stays cold. Sometimes the answer is adjusting the dampers in the ducts; sometimes the suite needs its own heat.
When It’s the Furnace
If the filter is clean and vents are open but airflow is weak everywhere, the blower may be slowing down or set to the wrong speed. See blower motor problems. If the air from the vents is cool, see furnace blowing cold air.
What David Checks
He measures the temperature rise across the furnace and the airflow, checks the blower speed setting, looks at the ducts he can reach for loose or crushed sections, and checks the dampers. You get his findings and any price before he changes anything.
Questions About Uneven Heating
Why are some rooms cold when the furnace is running?
Usually airflow: a clogged filter, closed or blocked vents, a blocked return grille, or a loose or long duct to that room. Check those first.
Why is my basement suite always cold?
One furnace often heats the main floor and the suite, with the thermostat upstairs. The furnace stops when upstairs is warm. Damper adjustment can help, or the suite may need its own heat.
Should I close vents in rooms I don’t use?
Partly closing a few vents is fine, but closing many can restrict airflow and make the furnace overheat. Keep most vents open and never block the return grilles.
Can a furnace service fix uneven heating?
Sometimes. A clean filter, correct blower speed and a checked airflow can help. If the cause is the ductwork, David explains what would fix it and what it costs.
Talk to David
Done the free checks and still have cold rooms? Tell David which rooms, which floor and where the thermostat is.
SkyLimit Heating & Gas is owner-operated. David answers the phone, does the work and gives you the price before he starts. Parts we supply carry a 1-year parts and labour guarantee. We work across Metro Vancouver and the Fraser Valley, Monday to Saturday, 9 AM to 9 PM, and don’t run a 24-hour line.
Call 778-892-5119 or request service online. Find your city in the furnace services directory.
Sources
Published by SkyLimit Heating & Gas. Updated . General homeowner information; gas, electrical and combustion work inside the furnace needs a licensed gas fitter.
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