Running fan continuously?

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We just replaced our 35 year-old furnace, 10 year-old AC with brand new Tranes. (sorry, don't have the model numbers.) The AC is a SEER 16 unit & the furnace is a high-efficiency (95% if I remember right.) -- the only thing disappointing about the installation is how ugly the exhaust pipe looks! The fan motor is a DC variable speed motor.
The installer recommended running the fan continuously to keep air circulating, even when temps are such it's not heating or cooling.. It also came with a fancy Honeywell AIQ thermostat. One of the settings on the thermostat is called "circ" -- the manual says that will run the fan "randomly", averaging 35% of the time. The house itself is 35 years old, seal broken on a lot of the windows, so not terribly air-tight, although it has 18" of insulation in the attic. (two story colonial.) Should we run the fan continuously, or use the "random" 35% setting, or have it only run ("auto") when actively heating or cooling?
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Ted Lee
Minnetonka, MN
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You bought equipment from someone whom I assume you trust. Why are you now second guessing his opinion? Has he done something that warrants not trusting him anymore?
Why is the exhaust piping ugly? Did they dual pipe the furnace? Did they use a concentric vent kit?
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I trust his judgement that it won't hurt the fan (e.g., shorten its life particularly) to run it continuously. He may not have the same trade-off between comfort and the cost of running it I do -- on the other hand, I read somewhere that it may only cost $30 a year to run the fan on low continuously!

Code here requires the fresh air intake to be 10 feet away from the exhaust, if that's what I think you might be referring to. What's ugly is the exhaust is just an "S" bend made out of two PVC elbows with a six inch or so piece of PVC at the end -- I was expecting (not based on any knowledge) only a short nicely rounded stub sticking out of the side, not such a big monstrosity.
Ted Lee Minnetonka, MN
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other hand, I read somewhere that it may only cost $30 a year to run the fan on low continuously!ot such a big monstrosity.

Some of the other guys may know better than I, but if I remember correctly a variable speed motor uses around 120 Watts or so; which is equal to a couple of 60 Watt light bulbs. So don't fret over it. Also motors are similar to car motors, it's the stopping and starting that does most of the wear and tear. So it's not going to kill the motor to let it run a little. The benefit to running the fan is that it keeps the air mixed up. If you spent the extra money on 16 SEER equipment then you should go ahead and spend a little more and fix the windows and any other air leaks you may have. They are costing you more than you think. Good Luck, Rodney
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Strange. I can't find anything with Google that has hard numbers about how much power those motors take! The few owner's manuals with specs on various furnaces I could find only talk about the gas (BTU) usage, not the electrical. I did find one chart from a public utility somewhere with a graph comparing PSC vs. DC motors on furnaces/AC's, low speed/high speed that looked like running at low speed it was 30 watts, but I wouldn't say it was definitive.
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Ted Lee
Minnetonka, MN
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go here... http://www.gamanet.org/gama/inforesources.nsf/vAllDocs/Product+Directories?OpenDocument
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http://www.gamanet.org/gama/inforesources.nsf/vAllDocs/Product+Directories?OpenDocument
Thanks. Lots of good information, but I couldn't find anything about the low-speed ("idle", if you will) power consumption of the blower motors, which is what I was wondering about -- what does it cost to run one continuously? On the other hand, it is a huge file and perhaps there is something near the end that talks about it. The listings of the individual furnaces didn't.
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Ted Lee
Minnetonka, MN
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I just took a class from John Proctor. His organization does extensive testing on HVAC units. A variable speed ECM unit uses around 60-80 watts on low and around 300+ watts on high. This can dramatically vary depending on the static pressure in the HVAC unit. As the static goes up from the design the higher the electrical consumption of the motor.
A single speed split capacitor may be in the 600+ watts an das the static goes higher than the design the CFM and energy consumption go down (yes the watts go down, Ive seen this in a static class where gauges are installed for static and watts and then restrict the duct and sure enough the watts go down).
Sorry no number on a 2 speed system
Hope this helps
Think and do Home Performance
Andy
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Interesting. I found a Canadian study that gave 22 watts on low -- big difference between 22 and 80. I wonder which is closer to right? I'll agree it could vary from motor to motor, but a 4-1 range for a "typical" house doesn't make much sense.
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Ted Lee
Minnetonka, MN
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We use metric watts in Canada.
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Are you gys saying that on AC units fan motor is running @100 milli. amps or on 120 vac @180 milli. amps. some one is smoking wrong weeds and is not me Tony

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milli. amps. some one is smoking wrong weeds and is not me

I don't know for sure what the others are talking about, but I'm talking about ECM DC motors which are alleged to take very little power when running at low speeds.
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Ted Lee
Minnetonka, MN
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No "alleged" about it... the Rheem RGPR-07 furnace only draws 113 watts according to GAMA
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milli. amps. some one is smoking wrong weeds and is not

Tony has it all wrong, he *is* the one smoking the weeds. His shit is *always* way off in left field.
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That's "PE" which is defined as "The electrical energey input rate supplied to the power burner (combustion air blower, fuel pump, damper motor) of a furnace or boiler operating under continuous burning (steady-state) conditions." I interpret that as what it draws when it's actively heating, and, with an ECM, presumably at full speed. I admit even that's pretty good, although there are other furnaces with even lower (not necessarily comparing apples to apples) but we have been talking about how much it draws when running on low and as far as I can that GAMA report doesn't address that.
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Ted Lee
Minnetonka, MN
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Since you seem unwilling to take our word for it, put your fan on low speed by switching from "auto" to "on" at the t-stat, take an amp meter and measure how many amps it draws. Then use Ohms law to figure the cost. Most of us have sat through enough classes given by the makers of this equipment and listened to their numbers about power consumption. That's one of the selling points of variable speed equipment. When we say around 120 watts we know because we have heard it over and over. Now unless they are lying to us I would say they know how much power their equipment uses. Rodney
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Code here requires the fresh air intake to be 10 feet away from the exhaust, if that's what I think you might be referring to. What's ugly is the exhaust is just an "S" bend made out of two PVC elbows with a six inch or so piece of PVC at the end -- I was expecting (not based on any knowledge) only a short nicely rounded stub sticking out of the side, not such a big monstrosity>
That could probably be done a little different if I understand what you are saying. We sell Trane (actually American Standard) and we normally just terminate with a 90 deg ell or a Tee. Rodney
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I would imagine it has everything to due with expected snow coverage.
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You're right. Didn't think about that. I'm in GA so snow is seldom an issue. Rodney
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Must be nice!
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