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Old 02-16-2014, 11:57 PM   #1
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I have a very general question and I hope you can answer with my limited info.

I have Kenmore (Goodman) high effenciency gas furnace that was installed in 2002. I recently had to replace the control board. I had a familt friend diagnos it and got thenpart and replaced it myself. Prior to this I have had to do nothing to this furnace amd it has run flawlessly for the 12 years.

I live in Pittsburgh Pennsylvania and as with most of the country, my furnace has been working overtime this year. I use my blower motor a good bit in the transition seasons just to keep the air moving in the house. I also have air conditioning that gets used a good bit in the summer.

My question is this: Is it more cost efficient to leave the blower motor on constantly than to have it switch on and off with the furnace/air conditioning? Also, In terms of wear and tear on the motor, is it harder for it to start and stop or to just run?

Thanks,
Rick

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Old 02-17-2014, 12:31 AM   #2
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Motors are like anything else, they could last 2 years or 20. I would say that keeping things serviced would last longer but not always true. I've seen well serviced blower motors only last a few years and I've seen blower motors packed with dirt run for a couple decades but that doesnt mean we should neglect them.

Yes, a motor that is left on constantly may last longer than one that is cycled quite often but basic psc motors are fairly cheap and running it constantly to extend its lifespan will cost you more in electricity over the course of a few years.

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Old 02-17-2014, 05:06 AM   #3
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Running the blower 24/7 can raise your electric bill by 30 bucks a month though.
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Old 02-17-2014, 12:03 PM   #4
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Originally Posted by beenthere View Post
Running the blower 24/7 can raise your electric bill by 30 bucks a month though.
That I guess depends on what your electric charge is, because if I do the math for my area, a 1/3 horse motor running 24/7 costs about $10 a month.

That being said.... if it's not running, it's not costing anything. However we also keep our fan running almost all the time. The temperature of the house stays a little more even, and we use our basement as living space as well so there is always the threat of radon gas build up without change of air.

I replace my motor (PSC) once every 3 years or so and the last one I got cost $68.
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Old 02-17-2014, 12:09 PM   #5
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Do the math. the motor uses 4 amps x 120 volts = 480 watts>500 watts = 1/2 a kilowatt. get your elec rate in cents/hr/kilowatt and you know the cost to run. in my experience after 10 yrs of continuos running the bearings will probably seize up soon. some people like the continuos airflow and others find it drafty. some people are willing to pay for that comfort or airflow so it is not necessarily the wrong thing to do. just have to buy a new motor sooner. stopping and starting does not hurt those motors but continuos run wears them out. PSC motors usually last 10 yrs running 24/7.
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Old 02-17-2014, 04:14 PM   #6
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That I guess depends on what your electric charge is, because if I do the math for my area, a 1/3 horse motor running 24/7 costs about $10 a month.

That being said.... if it's not running, it's not costing anything. However we also keep our fan running almost all the time. The temperature of the house stays a little more even, and we use our basement as living space as well so there is always the threat of radon gas build up without change of air.

I replace my motor (PSC) once every 3 years or so and the last one I got cost $68.
If your 1/3HP blower motor is running 24/7 and doing 1/3HP's worth of work, it is using 221 KWHs a month. So on a month that you would need no heating or cooling. 221 KWHs only cost you 4.5248 cents per KWH? Very cheap electric rate.
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Old 02-17-2014, 06:32 PM   #7
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we pay about 8c/kwh and if it uses .5 kw then that is roughly 4c/hr so it is not too bad. I tell my customers 4c/hr x 24 hrs/day = $1.00 day x 30 =$30/month which is not cheap either. You need to have a good reason to run it and pay that much though.
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Old 02-17-2014, 09:25 PM   #8
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Originally Posted by bcgfdc3 View Post

My question is this: Is it more cost efficient to leave the blower motor on constantly than to have it switch on and off with the furnace/air conditioning? Also, In terms of wear and tear on the motor, is it harder for it to start and stop or to just run?

Thanks,
Rick
I've never seen any compelling evidence that it is more cost efficient to leave one run 24/7. With average utility rates as they are I just don't see that ever happening.

As for starting and stopping, they are designed to do that. What you could do, now that the motor is 12 years old, is remove it, oil the bearings, clean the wheel and blow the dust from it.

Here is probably an example that isn't average. Mine was put in service 30 years ago this month and has seen conditions about as extreme as it can get for cooling and heating. It was removed at about 10 years for service, again at around 20 years and 2 years ago. We've named the unit Old Faithful.

To leave one run continuous there would need to be a reason other than motor efficiency in my opinion.
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Old 02-18-2014, 01:32 PM   #9
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If you do want to run the motor 24/7 have you considered upgrading the motor to an ECM motor as a replacement. They are quite a bit more energy efficient and have the ability to run at a much lower continuous speed than the standard PSC motor. I have installed equipment with a continuous fan speed which draws less than 1 amp at low speed continuous, ramping up to about 3 amps at high speed ( approx.1100 CFM)
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Old 02-18-2014, 08:58 PM   #10
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Quote:
Originally Posted by Bob Sanders View Post
That I guess depends on what your electric charge is, because if I do the math for my area, a 1/3 horse motor running 24/7 costs about $10 a month.

That being said.... if it's not running, it's not costing anything. However we also keep our fan running almost all the time. The temperature of the house stays a little more even, and we use our basement as living space as well so there is always the threat of radon gas build up without change of air.

I replace my motor (PSC) once every 3 years or so and the last one I got cost $68.
If you really want to have an efficient motor, you can install a GE Evegreen motor, or the Emerson Ecotech. They are both ECM type motors and are extremely efficient in recirculation mode. They also run at a very low rpm when there is no call for cooling or heating and when in recirc mode, use less than 100 watts.
I did the Evergreen motor in my unit and am very happy with it thus far.
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Old 02-18-2014, 10:05 PM   #11
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Don't forget to factor in more filter replacements too! If you're using the fancy filtrete filters or other high quality filters, they can get dirty in about a month or so versus 3 months with the fan cycling...so you can add another $10 a month or so to the "budget"

Also, electric motors are not 100% efficient. If you have a 1/2 horsepower motor, factor in about 20% wasted as heat energy lost in the windings of the motor.
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Old 02-18-2014, 11:01 PM   #12
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and depending on how well your ac ducts are insulated and if they run outside of the building envelope, running the fan could bring cold or hot into the air in the house.
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Old 02-18-2014, 11:42 PM   #13
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Thanks everyone for your insight. I will think about this some more. I was just curious to the pros thoughts.
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Old 02-19-2014, 01:19 AM   #14
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permanent split capacitance motors have start, run and common windings. the start winding takes the most beating as it heats up quickly when energized but is also the biggest winding but most times when I see a motor fail be it any motor is it the start winding that has come apart.

For compressors there is a start kit which takes the heat off the start winding as it slams the motor into full speed within a fraction of a second thus alleviating the heat and stress the start winding usually takes. Start kit also known as a compressor saver due to that fact.

But not available for regular motors.

more than a few variables decide a motor's fate, mainly duct design.
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Old 02-19-2014, 01:20 AM   #15
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and evaporator coil cleanliness, air flow blockage (coil and ducts) equating to static pressure, etc..

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