Setting fan to auto: cost savings?


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Old 12-19-07, 02:47 PM
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Setting fan to auto: cost savings?

My older house has a recently installed central heat/air, with gas heat. It works well enough, though the house doesn't have insulated walls, so the outer rooms are colder than the rest of the house. I have found that by creatively setting the dampers and running the fan in the on position instead of auto, the outer rooms are as warm as the rest of the house.

Will it cost me much more per month to run the fan in the on position instead of auto?

By the way, it is a 1000 sf house with two bedrooms, if the size makes a difference. The system does not serve my converted garage, just the original living space.
 
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Old 12-19-07, 03:11 PM
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If you have a reasonable electric rate and the blower motor on your furnace is a DC var speed, the cost to run continuously would be inconsequential. If the blower motor is a conventional AC motor, then that's a different story.

IMO
 
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Old 12-19-07, 03:32 PM
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Heat Pumps and Electric Heating > Setting fan to auto: cost savings?

i am sold on variable speed DC fans. I got one with my new furnace and I even saved money on AC plus had more confort.

Even if you have a non-DC variable fan, you can save money depending on your situation.

To get a level of comfort in some of your rooms without a fan running constantly, you may have to set your temperature on the thermostat in a different area higher to do this. - That is a waste of energy.

Running a traditional, older fan system will provide more uniform comfort and can save money IF you have a good return and supply system. A very important factor is the return air and vent sizes.

I learned this since I have a two level townhouse with an open stair that can become a wind tunnel with the resulting hot and cold areas. I have learned how to adjust my supply different between summer and winter to get the comfort and humidity and dust control. Fortunately, I have excess duct capabity for this on a one zone system.

As you see, every family and house has different needs and criteria. In any case, running a fan constantly gives you the opportunity to save in the long run.
 
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Old 12-19-07, 03:35 PM
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I am not sure if you mean the added cost of running the blower motor itself or the total heating cost.
TigerDunes is right about the costs of running the motor.
If you mean total heating cost then yes, running the fan will generate a higher heating bill.

The reason for this is that you are more evenly heating your house which gives your furnace a little bit more work to do.
You have to decide what comfort level you want and if you want to pay a bit more to do it.

If you are in a region that experiences sub zero temperatures running a fan continuously will help minimize condensation on your windows.
 
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Old 12-19-07, 05:17 PM
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I live in Oklahoma, so we do have temps below freezing during the evenings.

The furnace is a Goodman unit that is about seven years old. I'm certain it is not a variable speed, though I don't know if it is AC or DC.

Over the past few days, when I have run the fan continuously, I haven't noticed the gas burners kicking on any more frequently than before.

One of the replies mentioned that having good returns would help, and I am fortunate in that the house has returns in the living room, kitchen, and far bedroom (the one with the outer walls). Perhaps that is why I notice such an improvement in temp when running the fan continuously.

I may try running the fan in the "on" position just in the evenings when we are home. I can turn it back to "auto" when we go to bed, and during the day when the far bedroom is unoccupied.

I do expect it to cost more just to run the blower continuously, as I don't know if the blower is AC or DC. I appreciate your mention of it so I can just run in the "on" position during part of the day.

Thanks again for your input.
 
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Old 12-19-07, 09:15 PM
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Wink

I may try running the fan in the "on" position just in the evenings when we are home. I can turn it back to "auto" when we go to bed, and during the day when the far bedroom is unoccupied.
From what you said of the home Id go with your plan above . Id say the furnace you have has a AC motor on it. You can check and see what speed it is set on most time the heat is a low speed and the AC is a higher speed. So you might want to cut it down cause ON will be high for AC. Id sure think about insulation in the walls come summer.
 
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Old 12-20-07, 06:36 AM
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The fan speed seems consistent, so I'm sure you're right about it being an AC motor.

As far as insulation is concerned, I guess the builders in our area thought the brick walls were sufficient, as compared to the cost in 1950 of insulation. It appears that I would have to pay someone to do some of the foam insulation that they squirt in through holes in the drywall. I'm not sure if the value of the house it is worth the cost of the insulation job. My natural gas bill is usually about $65/month, and my bill is on the gas company's averaging program. I'm afraid it would take much longer to recover my costs than I plan to live in the house.
 
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Old 12-20-07, 08:38 AM
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Brian, You also might look around at some of the different thermostats. There are several available that automatically cycle the fan every hour for a set or programmable amount of time, keeping the air moving without running the fan constantly. Both my thermostats have this feature and, in the winter, I set them to run the fans for 10 minutes every hour. I've found the result to be as acceptable as leaving the fans on all the time, but without any noticeable increase in the electric bill.

Doug M.
 
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Old 12-20-07, 09:05 AM
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Great tip! I was planning to get a programmable thermostat anyway. Thanks!
 
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Old 12-20-07, 10:22 AM
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As you know Fan left in the on potion all the time help circulate the air and help with cold and hot spots. They also help keep windows from forming frost and filter the air to help improve IAQ.
 
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Old 12-20-07, 08:02 PM
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Originally Posted by airman.1994 View Post
As you know Fan left in the on potion all the time help circulate the air and help with cold and hot spots. They also help keep windows from forming frost and filter the air to help improve IAQ.
I wish I had known about how keeping the fan always on could help with condensation on the windows. We had old steel casement windows that were really bad about condensation during the winter. It had made them quite rusty. We bit the bullet and had replacement windows installed last year, so no more condensation.
 
 

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