Home & Garden

Leave Furnace fan On or Off

  • Last Updated:
  • Aug 16th, 2018 6:52 am
[OP]
Member
Nov 11, 2007
218 posts
4 upvotes
Cambridge

Leave Furnace fan On or Off

When I have the furnace in heating or cooling I leave my fan on to circulate the air in the house ( bungalow). I have a new high efficiency furnace and have been told that I should leave my fan on 24/7 even when the furnace is off and I have all the windows and doors open. I have searched around and have not found a definitive answer. I can see the benefits of running the fan when the house is closed up and the heat or cooling system is functioning. Not sure what benefits are to be gained running the fan when all windows etc are open. Appreciate your thoughts on this subject. Thanks in advance.
27 replies
Deal Addict
Jun 17, 2009
1525 posts
117 upvotes
richmondhill
we just leave ours on the automatic setting
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Deal Addict
Jul 3, 2017
2994 posts
2042 upvotes
Leaving the fan on 24/7 will cost you on your electric bill, as well as reducing its lifespan. As you say, it's not needed when the windows are open, so it doesn't seem like a good idea.

The fan is usually either wired to come on automatically with the furnace or AC, or else it's controlled by the thermostat via the G wire. In the latter case the thermostat turns it on and off as needed. If you have a smart thermostat, you can usually set the fan to Auto or On with the thermostat controls. If it's a smart WiFi thermostat, you can do that remotely or set rules for how you want it to work.
Deal Fanatic
Feb 9, 2006
9340 posts
3301 upvotes
Brampton
It depends.
If you have an furnace with an ECM motor with a special low contunous mode sure leave it 24/7 to circulate air and aids in filtering the air thru the furnace filter. This special low mode should be so low that it doesnt negatively affect humidity in the cooling season by accelerating evaporation of water from the A coil.

If you have an older PCM motor and no special modes. It's best to leave it off until you need it.
I personally don't believe in using cycling from smart thermostats for a number of reasons.
[OP]
Member
Nov 11, 2007
218 posts
4 upvotes
Cambridge
I should have mentioned I have an ECM motor and an Ecobee smart thermostat. Thanks so far for the input.
Deal Addict
User avatar
Oct 12, 2007
3567 posts
726 upvotes
Ottawa
I run ours on continuous. We have a variable speed, DC motor on our furnace. Continuous has eliminated hot or cold spots in the house. Yes, I am probably paying $15/month for the electricity to run it but - in my house - it's worth that small price for the additional comfort it provides.
Deal Addict
Aug 29, 2011
3379 posts
1076 upvotes
Mississauga
Same as the above poster. Evening out the temperature between the storeys in the house means I don’t have to run the a/c as much to keep the second floor comfortable and the basement from becoming a meat locker.
Newbie
Mar 13, 2006
50 posts
24 upvotes
Bowmanville
Echoing the above two posts, the circulation provided is great.

For your house, remember that builds vary and there is no steadfast rule. This approach may not make as much a difference in a bungalow, but in our two storey the added circulation really helps the rooms furthest from the furnace. I don't care if it costs us more in electricity -- it's worth it in comfort.
Deal Expert
User avatar
Dec 12, 2009
16580 posts
5138 upvotes
Toronto
CaptSmethwick wrote:
Aug 12th, 2018 11:02 am
I run ours on continuous. We have a variable speed, DC motor on our furnace. Continuous has eliminated hot or cold spots in the house. Yes, I am probably paying $15/month for the electricity to run it but - in my house - it's worth that small price for the additional comfort it provides.
I run my fan 24/7 for exactly this reason.
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Tangerine Bank
Sr. Member
Apr 12, 2008
645 posts
109 upvotes
I have mine run for "X minutes in 60 minutes" setting from the Nest.
Deal Addict
Nov 2, 2005
3219 posts
742 upvotes
Ottawa
24/7, helps even out the temperature and humidity levels in the house.
Member
Jan 7, 2013
328 posts
117 upvotes
Whitby Ontario
One small issue with 24/7 fan use during AC weather is that you end up re-humidifying all the moisture left from your AC coils into the air as the fan continues to run.

But it helps even out floor temperatures for 2 story homes.
Member
Jan 13, 2007
282 posts
158 upvotes
Toronto, Ontario
Would it make sense to leave the furnace fan on circulation mode even if it's a single speed motor?
Deal Addict
User avatar
Oct 12, 2007
3567 posts
726 upvotes
Ottawa
woofster wrote:
Aug 13th, 2018 1:30 pm
Would it make sense to leave the furnace fan on circulation mode even if it's a single speed motor?
The answer to that question is in the assessment of the comfort impact of circulation mode against the costs - only you can decide if it's "worth " it. I have run our two storey house on continuous mode for 28 years - including years when we had a two speed fan.
Deal Fanatic
Feb 9, 2006
9340 posts
3301 upvotes
Brampton
woofster wrote:
Aug 13th, 2018 1:30 pm
Would it make sense to leave the furnace fan on circulation mode even if it's a single speed motor?
No motor is single speed really. They usually have multiple taps.
Usually these types of motors are PCM and will draw see 600-800W continuously since a call for fan usually runs it at the "Hi" or AC fan speed
An ECM motor equipped HVAC system usually has a special circulation speed that draws under 100W, usually 50.

If want to use Continuous with a PCM motor I would bypass the thermostat and look for the "Cont" header on your furnace board and hook the low tap to it. At least you won't be drawing 600-800w.

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