Furnace Fan "auto" vs "ON"

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Bob wrote:

Could you explain why?
The bearings are being worn whenever the shaft turns. What typically breaks on these,....... the bearings.
What wear is caused by starting and stopping the motor? These typically do not have a centrifugal switch or anything like that so what's the problem with starting and stopping?
On a normal winter day my furnace and blower run <25% of the time, seems like a waste of energy and wear and tear on the blower bearings to run the blower 24/7.
Mark
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At the classes I've gone to, the teachers said that stopping and starting was worse, and that once they get up to speed, there's very little strain on a motor of this type. I don't remember anyone ever asking them why. I always assumed it was from the heat generated while the armature was straining to get up to speed but still didn't have enough air flow to cool it properly. As for the bearings, I don't know if sleeve or ball bearings makes a difference, but I assume the blower wheel must be balanced properly to cause minimal bearing wear.

going,
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but it takes only a few seconds to get up to speed...
I find it hard to believe that any significant heat builds up in 5 seconds compared ot the heat that builds up runnning 24/7....
Imagine starting the blower..... then as soon as it gets up to speed, stopping it, and checking the motor windings and armature temperature .... compared to letting it run all day then checking the temperature..
thanks
Mark
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Mark, You have no idea what you are talking about so you should quit while you are ahead. Go buy a clamp on amp meter and watch the motor load on start up. Then watch one while you hold the motor from running while it is trying to start. Do that about 2 or 3 times and feel how hot the motor gets. You may then begin to understand. Bubba
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Mark & Bob, The blower motors are designed to be able to run constantly without damage to the bearings or windings. Just ask any motor manufacturer. I have been to many motor seminars & the main failure mode is HEAT. A motor with restricted air flow will run hot and die an early death. Starting causes some strain on motors but dirty or restricted filters cause overheating which will damage motors. A blower motor should last as long as the furnace if it has enough air flow to keep it cool. That is if it runs constantly OR cycles.
Running the fan set to on will increase humidity when cooling by as much as 15% in high humidity climates. This is because when the compressor shuts off the water left on the coil will re-evaporate into the air stream. Get a data logger to record humidity and try it both ways. I did. A Lennox manual titled "Equipment Selection in Humid Applications" came to the same conclusion.
My fan motor on my 2.5 ton heat pump indoor unit draws 2.2 amps at 240 volts. Just over 475 watts at 0.9 power factor. at my utility rates that is about 4 cents an hour. That is just under $30.00 per month when running 24/7.
I leave mine set to auto. If you have cheap electricity or a different climate or both, feel free to set it to ON.
The advantages are it will even out temperatures and filter the air better. The disadvantages are high summer humidity in many climates, high electric bills and drafty feeling in the winter. The best time to run the fan set to ON is spring & fall.
Stretch
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Stretch,
Thanks for the input. I can see where setting the fan to 'on' in humid climates can increase humidity. My experience is limited to my particular climate. I wonder if Lennox was only talking about properly sized cooling systems when they say "as much as 15%".
I have hydronic baseboard heat with straight air in the attic. With the blower on, my heat is more even, because it pushes the heat back down to the floor.

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Thanks for the input. I can see where setting the fan to 'on' in humid climates can increase humidity. My experience is limited to my particular climate. I wonder if Lennox was only talking about properly sized cooling systems when they say "as much as 15%".
I have hydronic baseboard heat with straight air in the attic. With the
blower on, my heat is more even, because it pushes the heat back down to the floor.
Bob, Yhe 15% was what I measured with my data logger using my system. My unit is properly sized. Lennox does not give a percentage in their manual.
Stretch
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Then i would suggest that you leave your car running all the time. You don't have a clue.
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Sorry, but I never saw an air-cooled direct-drive car motor. And even if they had one, I fail to see the benefit unless you're living in the car and filtering the air.
wrote:

It's
going,
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c_shah wrote:

It is to be used by a service man.
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Any and all if thats what you want.
Mine only gets shut off for service. Other than that, the fans on 24-7.
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c_shah wrote:

The only times I've left mine on "ON" were during parties in the winter when I'd have many guests over. The body heat generated by each guest is enough to raise the temperature of the room a few degrees above normal, making the furnace not run at all. After 3-4 hours the main floor where all the guests are becomes 2-4 degrees hotter than the rest of the house, and the air starts getting a bit stuffy from all the people and the lack of air circulation. Often the windows will start to fog up from the extra humidity (from all the cooking, guests talking and drinking, etc.)
I leave the fan on ON to get better air circulation during those times. The whole house stays at a much more comfortable and constant temperature, the air is less humid and stuffy, and the windows don't fog up.
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...and it's really important to do that if you're serving a bean dish like chili ;-)
Patrick
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Is there something wrong with my furnace? If I leave the fan "ON" there's a big boom when the heat kicks on when the gas lights. I just assumed that the gas was being sucked up by the fan and torched when it lit.
If I leave it on "AUTO" it works just fine.
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johnny wrote:

That does not sound normal to me.
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Yeah. I better just leave it on "AUTO".
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johnny wrote:

Yeah, that you can pretend that the heat exchanger isn't cracked.
hvacrmedic
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Ignorance is bliss. What I don't know about can't hurt me.
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johnny wrote:

What you don't know can certainly hurt you.
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Patrick Cleburne wrote:

Uhh, chili isn't a bean dish, it is a green dish.
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