Fan "On" or "Auto"?

[wobble]

Running my furnace with fan "on" certainly keeps the temperatures uniform throughout my house. I'm aware of some of the pros and cons of doing this, but I haven't read much about what the extra cost of this practice might be.

I couldn't find the power consumption for my Carrier 58MVC, but, according to data for a comparable Trane, the draw appears to be from 100 watts to 290 watts on low speed, depending on static pressure. With my electric prices, this is somewhere between $8 and $25 per month, not a trivial amount. To get a more realistic number I should deduct the time the furnace is active, so these numbers are certainly worse case.

It seems to me that constantly circulating room air through the crawl space ducts, though insulated, would result in an appreciable loss of heat, thus leading to higher gas consumption. I have no idea how to calculate that.

Any thoughts?

[seadragon]

I keep my fan on low all year except when I have the windows open. I've never done the math to figure out how much it costs, but my electric bills aren't that crazy.

Reasons I keep the fan on all the time:

- more even temps in the house
- ERV fresh air is ducted into the return plenum
- prevents "dirty sock" smell from AC since the coil dries off faster

One argument for keeping the fan running I've read many times is that it cycles on and off less and is easier on the motor. I've never understood this one since my furnace shuts off the blower while the burner ignites, so it stops and starts the same amount whether its set to Auto or On.

[platchford]

Running my furnace with fan "on" certainly keeps the temperatures uniform throughout my house. I'm aware of some of the pros and cons of doing this, but I haven't read much about what the extra cost of this practice might be.

I couldn't find the power consumption for my Carrier 58MVC, but, according to data for a comparable Trane, the draw appears to be from 100 watts to 290 watts on low speed, depending on static pressure. With my electric prices, this is somewhere between $8 and $25 per month, not a trivial amount. To get a more realistic number I should deduct the time the furnace is active, so these numbers are certainly worse case.

It seems to me that constantly circulating room air through the crawl space ducts, though insulated, would result in an appreciable loss of heat, thus leading to higher gas consumption. I have no idea how to calculate that.

Any thoughts?

Yeah, my issue with running the fan in the on position if the ductwork is located in unconditioned space is exactly that. The heat loss/gain that your unit has to make up for by running more frequently. Yes, its hard to quantify exactly how much it is exactly. You have to weigh the pros and cons really. Personally, I have a VisionPro stat that has a 'Circulate' option that I use in the cooling season... during the winter I use Auto... and my ductwork is all in conditioned space.

[gary_g]

Personally, I have a VisionPro stat that has a 'Circulate' option that I use in the cooling season... during the winter I use Auto... and my ductwork is all in conditioned space.

I have the same t-stat and operate the fan exactly as you do.

I'll run the fan "on" in the summer at nights to drown out the street noise for better sleeping.

Take care.

[badtlc]

IMO, running it when you aren't home is a waste.

I also have a visionPRO IAQ and I only use 'on' mode during the heating season. Also, it is only set to "on" during the periods of the day when the lower level of the house is being used. This is typically from 5pm to 10pm. All the bedrooms are upstairs so no point in running it at night and definitely not during the day when everyone is gone.

[skizot]

IMO, running it when you aren't home is a waste.

I also have a visionPRO IAQ and I only use 'on' mode during the heating season. Also, it is only set to "on" during the periods of the day when the lower level of the house is being used. This is typically from 5pm to 10pm. All the bedrooms are upstairs so no point in running it at night and definitely not during the day when everyone is gone.
So are you manually turning it to on from 5pm to 10pm every day? It doesn't have a way to set time periods for "on" operation, does it? Just curious because I have the same stat.

[badtlc]

So are you manually turning it to on from 5pm to 10pm every day? It doesn't have a way to set time periods for "on" operation, does it? Just curious because I have the same stat.

You can program the fan setting from auto to on in the same time periods and methods that you set your 4 different temperature settings for each day. I do not manually set/override anything.

On the weekends, during heating season, I set the fan to run in 'on' mode from around 9am to 10:30pm since we are home most of that time. I like having the t-stat do it all for me.

[skizot]

You can program the fan setting from auto to on in the same time periods and methods that you set your 4 different temperature settings for each day. I do not manually set/override anything.

On the weekends, during heating season, I set the fan to run in 'on' mode from around 9am to 10:30pm since we are home most of that time. I like having the t-stat do it all for me.

Nice, I'll have to look into that.

[skizot]

Just looked at the manual. It looks like the fan settings can be changed for each time period that you use for heat/cool, but not independent of those periods. Still helpful, but unfortunate that it's not truly independent.

[badtlc]

Just looked at the manual. It looks like the fan settings can be changed for each time period that you use for heat/cool, but not independent of those periods. Still helpful, but unfortunate that it's not truly independent.

correct. You'd still have to reset the fan mode programming when switching from AC to heating and vice versa. I'm not complaining about changing settings twice a year.

[skizot]

correct. You'd still have to reset the fan mode programming when switching from AC to heating and vice versa. I'm not complaining about changing settings twice a year.
I was referring to the time periods themselves. For example, your "arrive home" period might be from 5:00 PM - 10:00 PM, and the period after that from 10:00 PM to 7:00 AM. What I meant by independent was being able to set the fan to run in on from say 8:00 PM - 12:00 AM (independent of the heat/cool time periods).

Still a useful feature, nonetheless.

[commerce48]

I keep my fan on low all year except when I have the windows open. I've never done the math to figure out how much it costs, but my electric bills aren't that crazy.


Your blower should be using about 75 watts at low speed. If your electric costs are 12 cents per kW, that is about 22 cents a day to run always on or $80 a year. From that you would have to subtract the time your system would be running anyway, or times you have it off.

If your comfort increases from running always on to the point where you can decrease your heat a couple of degrees, or increase AC temp a couple of degrees, that may end up saving you money.

[SerafinsAC]

Running the fan in "ON" with a good air filter will help clean your air too.

[NorthWet]

Decided to give this a shot during heating season which we are in. I set the fan to on during the periods we are home but a quick question for you guys. Does the fan status area on the stat show on and auto at the same time? Mine does.

[HPGui]

Decided to give this a shot during heating season which we are in. I set the fan to on during the periods we are home but a quick question for you guys. Does the fan status area on the stat show on and auto at the same time? Mine does.

Typically, "ON" by itself means the fan is running 100% of the time. "AUTO" means the fan runs when needed for a cooling or heating call. If available on your stat, you might also see "CIRC" which means the fan will run for 15 minutes or so every hour + when needed on colling/heating calls. If you set an automatic schedule calling for certain settings at certain times (including fan settings at specific times), you can then set the fan to "AUTO" and it will follow your choices. If so, you may see both "AUTO" and the "CIRC" at the same time (and perhaps even "AUTO" and "ON" simultaneously.) If you only see "ON" or "CIRC" by themselves, that means you have selected those fan settings manually, not via a schedule.