Blower motor speed

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Blower motor speed

Postby bender » Fri Sep 02, 2011 10:56 pm

I have a York furnace with AC. In the winter my family room is always chilly so I thinking of trying to get more heat into the room one of two - 1) Adding a duct fan or 2) increasing the blower fan speed.

The unit is a York ‘Stellar’ GFA Model P3UCD20N09101A and it has a blower motor that has two wires for connection. One is red (slow) and the other is blue (medium). The red wire is connected to the source via an inline type wire connector and the blue wire is disconnected and capped with a clear plastic sleeve. I'm thinking of changing the source to the blue wire (medium speed) to increase the air flow.

My second approach is to add a duct fan but I would like to wire the fan into the unit so that it comes on when the blower motor is on. I know there are duct thermostats that would do basically the same thing but I'm thinking the direct wiring to the unit would be more accurate.

Is my first approach a good idea and if so why wasn't it wired to the medium speed to begin with?

For the second approach I'd need to know how to connect the duct fan to the unit correctly?

Any help would be appreciated.
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Postby heatseeker » Tue Sep 06, 2011 9:16 am

did you get the duct work inspected or balanced ? do you have dampers is your cooling coil clean if you have one you may need to installa bigger duct to that room or balance with dampers. A duct fan is not really a good idea for heat it will pull to much air thru the furnace causing low heat transfer.
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Postby cascadehvac » Thu Sep 08, 2011 11:49 am

the best way to increase air flow to one room is to dampen down some other rooms that may have extra airflow. speeding the fan up may help a little. the faster the fan the less heat will come out of the vents tho. an inline fan will not help.
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Postby bender » Mon Sep 12, 2011 9:05 am

Thanks for your resonses cascadehvac and heatseeker.

The ducts are as they were when the house was built so I'm assuming they were inspected and balanced but this could be a bad assumption.

I have tried closing the vents in other rooms but this doesn't seem to help much for this one leg of the vents.

I haven't checked the cooling coils but the weak air flow from this one vent isn't a problem that has been building over the years, the airflow out of this vent has been weak since the house was built.

I'm a little confused about the response for speeding up the fan, won't increasing the fan speed increasse the airflow? When you say 'less heat will come out of the vents' do you mean the air that is coming out will be cooler in temp?

Sounds like both responses agree that an inline fan will not help. So short of adding additonal vents to the room maybe speeding up the fan is worth a try? Will changing the speed of the fan damage the furnace in any way just for a trial period?
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Postby heatseeker » Tue Sep 13, 2011 10:10 am

increasing air flow will lower the heat transfer when your furnace is operating beacause the air will be traveling to fast to pick up all of the heat in the heat exchanger. It seems as though you are at a point where you either need to upgrade your duct work or your furnace or both.
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Postby JackNg » Sun Nov 27, 2011 4:56 am

HVAC system helps you out to do the Air - *.org/ You can either do yourself the air duct cleaning or hire somebody else.
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Postby Freon » Sun Nov 27, 2011 10:12 am

Your best option is to improve the ducting going to the coldest room. If possible, increase the duct diameter, remove any 90 degree elbows (use 2@45) and use metal duct. To know if increasing the blower motor speed will help, you need to know the air flow (cubic feet per minute... cfm) your duct system can handle. That's an easy exercise and a good one for you to better understand your system.

You'll learn that a 6" diameter duct can handle ~110 cfm, an 8" Diameter duct ~230 cfm... etc. Adding up all the supply register duct sizes and also the return duct sizes will give you an idea of what your duct system can handle. The return (air back into the furnace) cfm should equal the supply (air out to rooms) cfm should equal the blower speed setting cfm. The blowerr cfm will be on the furnace data sheet for each speed. If your ducting can handle the increased cfm, then changing the motor tap to the higher rpm will help. As pointed out, the air exiting the supply registers may be a bit cooler but the heat transfer will not be affected so furnace efficiency will be the same... it may even be a bit more efficient.
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Postby MTI STUDENT » Mon Dec 05, 2011 3:56 pm

Before speeding up the fan check the temp rise . This is done by using a probe thermometer first in the area inside were the filter goes and second take a screw out of the duct if possible as close to the plenium as possible but out of sight of the heat exchanger . You then subtract the supply temp from the return temp . Your owners manual should give you recomended range for this . If not contact the manufacturer .
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Postby heatseeker » Mon Dec 05, 2011 4:52 pm

Good luck getting info from manufacturer, especially if furnace is old.
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Postby how » Wed Dec 07, 2011 12:24 am

If you have a heating distribution difficulty, have you considered a 2 speed fan set up with a continuous low speed red operation. This will help even out the temp differences between the different rooms?
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