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Furnace fan - AUTO or ON?

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  • Dec 14th, 2009 7:16 pm
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Newbie
Nov 30, 2007
85 posts
Ottawa

Furnace fan - AUTO or ON?

When to keep the furnace fan ON vs AUTO? Winter vs Summer?
29 replies
Deal Expert
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Aug 9, 2004
21622 posts
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Mississauga
I use auto most of the time. it means the blower will run when the furnace/air cond kicks in, but not at other times.
When I want to recirculate the air (say the basement is cold in the summer, but its not cold enough to justify running the ac, I put it on to "on" which makes the blower run constantly.
Thanks for the memories, RFD.
Good-bye.
Deal Addict
Jan 5, 2003
3065 posts
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Toronto
Auto: turns on the blower only when the A/C or furnace is on.

ON: means the blower is blowing constantly. Uses more electricity, but cleans the air more, as more air is forced through your air filter. Also evens out the temperature in your house as air is constantly being moved around the house.

This doesn't necessarily mean summer or winter. Most people have it on one setting year-round. If you have uneven temps around the house in summer, you will in winter, as well.
Deal Addict
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Oct 12, 2007
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Ottawa
We keep ours "on" year round. As a consequence, heating and cooling is very even and dust is well under control. We pay higher electricity bills and go through more furnace filters but we'll spend less on heating and cooling because there are no cold/warm spots in our house. I consider the expense a wash and go with the option that gives us the greatest comfort (leaving it "on").

In theory, you can move it to "auto" for those months when you are neither heating nor cooling but I would certainly forget about it and eventually have it set where I don't want it... :rolleyes:
Sr. Member
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Jul 13, 2006
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I leave mine on "VENT", which is an option on my thermostat (Noma 7-day programmable). It turns the fan on approx 15 minutes of every hour to circulate air, but doesn't run all the time. I find it a nice balance and have tried "ON" and "AUTO", but prefer VENT... a happy medium. If I did not have this option, I'd definitely leave it on "ON" as I really can tell a difference in dust, comfort, and freshness levels between AUTO and ON.
Deal Addict
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Sep 5, 2004
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Guelph, ON
I have Auto, Low, Medium and High Speed Fan Control with my Carrier Infinity System and leave it on Low speed when home in the evening and overnight, but Auto during the day. It's a DC Motor so practically no cost to run the fan.
Deal Addict
Aug 24, 2002
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CaptSmethwick wrote:
Oct 14th, 2009 7:50 pm
We keep ours "on" year round. As a consequence, heating and cooling is very even and dust is well under control. We pay higher electricity bills and go through more furnace filters but we'll spend less on heating and cooling because there are no cold/warm spots in our house. I consider the expense a wash and go with the option that gives us the greatest comfort (leaving it "on").

In theory, you can move it to "auto" for those months when you are neither heating nor cooling but I would certainly forget about it and eventually have it set where I don't want it... :rolleyes:
Unless your fan is DC or has been wired so that 'on' is low speed, you are wasting a lot of electricity to get a lot less benefit than you think.

You mention putting it Auto for the moderate times of year... but you know the difference would be so neglible that you would forget to change it. I would say that's a strong indicator Auto IS the best setting. If it comes to the middle of summer or winter and you are actually noticing cold or warm spots, then flick the switch. Easy. Saves lots of money. Saves pointless wear on your system. Saves the planet.
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Aug 24, 2002
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I'm curious about people claiming a difference in dust level idling your fan 24x7x365.... I mean, really? I've tried both and there is a miniscule difference if any. Is it that maybe expectations are influencing your perception? You expect less dust, so you look and declare "that's less dust". How would you even measure that?!?

Something to keep in mind is a fact that air filter sales companies market very hard to delude you about: the furnace filter is mainly to protect your equipment, not clean the breatheable air.

They know that people won't pay 10 or 20X the normal value of a filter if it's for some mundane reason, so they prey upon people's motivational buttons and sell them on the idea of cleaner, healthier air. They show sunlight falling down an impossibly clean hallway, and baby sleeping soundly, his little chest rising and falling. But unless you have a real actual air cleaning system, there's not much reason to use the boutique filters, and they aren't doing much to change the air you are breathing.
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Oct 12, 2007
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Ottawa
I'm not going to argue right or wrong on this one - it's a personal preference and I stated mine. Keeping your fan on 24/7 costs at most ~$150/yr in electricity (the true delta depending, obviously, on your electricity rates and how long the fan would run in the "auto" setting). In favour of keeping it in the "on" setting: better dust collection, evening-out of the air temperature, a reduction in on-off cycling of your a/c unit and furnace burner, better diffusion of odors, and the movement of air reducing condensation on windows (in winter). The downsides: costs and the air movement can feel drafty to some.

Most home comfort experts recommend that you leave it "on" but switch to "auto" if you find it too expensive or don't like its "drafty" feel. But, then again, most home comfort experts are probably part of that covert furnace filter cartel conspiracy about which we've now been enlightened. :rolleyes:

I personally think that there are more benefits from an "on" setting in a two storey home where hot air can migrate upstairs, creating distinct temperature zones in the home. Using a ceiling fan will partially mitigate that but won't do as good a job as a furnace fan.
Sr. Member
Nov 24, 2005
697 posts
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Southwestern Ontario
stealth wrote:
Oct 14th, 2009 7:21 pm
I use auto most of the time. it means the blower will run when the furnace/air cond kicks in, but not at other times.
When I want to recirculate the air (say the basement is cold in the summer, but its not cold enough to justify running the ac, I put it on to "on" which makes the blower run constantly.
This is what we do, I hate running the A/C if the fan will do
Deal Addict
Aug 24, 2002
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CaptSmethwick wrote:
Oct 15th, 2009 7:18 am
I'm not going to argue right or wrong on this one - it's a personal preference and I stated mine. Keeping your fan on 24/7 costs at most ~$150/yr in electricity (the true delta depending, obviously, on your electricity rates and how long the fan would run in the "auto" setting). In favour of keeping it in the "on" setting: better dust collection, evening-out of the air temperature, a reduction in on-off cycling of your a/c unit and furnace burner, better diffusion of odors, and the movement of air reducing condensation on windows (in winter). The downsides: costs and the air movement can feel drafty to some.

Most home comfort experts recommend that you leave it "on" but switch to "auto" if you find it too expensive or don't like its "drafty" feel. But, then again, most home comfort experts are probably part of that covert furnace filter cartel conspiracy about which we've now been enlightened. :rolleyes:

I personally think that there are more benefits from an "on" setting in a two storey home where hot air can migrate upstairs, creating distinct temperature zones in the home. Using a ceiling fan will partially mitigate that but won't do as good a job as a furnace fan.
Agree with most of this except the dust collection/air cleaning. The air filter is for keeping dirt out of the furnace motor, not cleaning air in your living space. You may be improving your air quality but if it's only by 0.000000000001% then it that really worth wearing out your equipment and burning a couple hundred in fuel every year?

Most practical experts recommend the Auto setting. That's why it is the auto setting after all.
Deal Fanatic
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Jul 4, 2004
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You'll know the answer when the motor eventually burns out and if you're not handy to buy and change it yourself. ;) I think a ceiling fan made for continuous use would be better if you must.
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Jun 27, 2007
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I've used ON setting entire summer and after a couple of hydro bills almost doubling, decided to go back to AUTO. In my case, consumption was 12-15 kWh per day (running the fan). What have I learned?
- air wasn't noticeably cleaner, still plenty of dust
- temperature was somewhat evenly distributed, esp in the west facing rooms late afternoon/evening

If I notice colder/warmer spots, I run fan constantly for 1-2 hours and voila!
Member
Sep 28, 2009
333 posts
1 upvote
London
The new furnaces are designed to be on constantly. With the DC motors in the newer models, having it on 24/7 only costs a couple of bucks a month.
Member
Sep 28, 2009
333 posts
1 upvote
London
dlhunter wrote:
Oct 15th, 2009 2:04 pm
I've used ON setting entire summer and after a couple of hydro bills almost doubling, decided to go back to AUTO. In my case, consumption was 12-15 kWh per day (running the fan). What have I learned?
- air wasn't noticeably cleaner, still plenty of dust
- temperature was somewhat evenly distributed, esp in the west facing rooms late afternoon/evening

If I notice colder/warmer spots, I run fan constantly for 1-2 hours and voila!
How old is your furnace? Does it have a DC motor?
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