HVAC Tips
Should You Run Your Furnace Fan in Summer?
Running your furnace fan on ON instead of AUTO circulates and filters air all summer — great for even temperatures and air quality, at a small electricity cost. Here’s when it’s worth it.
What does the furnace (HVAC) fan actually do?
The blower fan inside your furnace moves air through your ducts — in winter it pushes heated air, in summer it pushes cooled air from your A/C. On its own (without heating or cooling) the fan just circulates and filters the air in your home, pulling it through the furnace filter and pushing it back out the vents. It doesn’t cool the air, but moving air feels cooler and evens out hot and cold spots between rooms and floors.
ON vs AUTO — the difference
| Setting | What it does |
|---|---|
| AUTO | Fan runs only when the furnace or A/C is actively heating/cooling, then stops. |
| ON | Fan runs continuously, circulating and filtering air even when not heating or cooling. |
Running the fan continuously in summer — pros & cons
Pros:
- More even temperatures between upstairs and basement
- Constant air filtering — helpful for dust and allergies
- Reduces stuffiness and humidity pockets
Cons:
- Uses some electricity (a modern ECM/variable-speed blower is cheap to run; an older PSC motor costs more)
- The filter loads up faster, so check and change it more often
- In very humid climates it can re-introduce humidity — less of an issue in dry Alberta
So should you run it?
If you have a newer variable-speed furnace and want more even temperatures and cleaner air, running the fan on ON in summer is usually worth the small cost — especially in two-storey Edmonton homes where the upstairs runs warm. If you have an older single-speed blower and want to save power, AUTO is fine. Either way, a clean filter and clean ducts make the fan far more effective — see our A/C coil & central vac cleaning and furnace & duct cleaning.
Furnace fan in summer — FAQ
What does running the furnace fan do?
It circulates and filters the air in your home through the furnace filter, evening out temperatures between rooms and floors. It doesn’t cool the air, but moving, filtered air feels fresher and more comfortable.
Should I run my furnace fan continuously in summer?
With a newer variable-speed furnace it’s usually worth it for even temperatures and cleaner air at a low electricity cost. With an older single-speed blower, AUTO saves more power. Check your filter more often when running ON.
Does running the fan cool the house?
No — the fan alone doesn’t lower the temperature, but circulating air makes a room feel cooler and spreads your A/C’s cooled air more evenly.
Does running the fan use a lot of electricity?
A modern ECM/variable-speed blower costs only a little to run continuously. An older PSC motor uses more, so factor that in if your furnace is older.