Higher CFM blower for furnace


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Old 11-21-22, 05:07 AM
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Higher CFM blower for furnace

My home had an addition back in the 90s, I dont know if the current furnace was installed before or after the addition but the heat barley reaches the addition. The duct work runs through a crawlspace thats sealed from the basement and is vented to the outside and the duct is somewhere around 30ft and branches to new bathroom and master bedroom. Its 8 inch duct. When the heat is on you can feel warm air coming out of vent but with no real force and always leaving the addition about 5 degrees colder than rest of house. I even have the vents closed in dinning room (where thermostat is) and kitchen closed to try and keep the furnace running longer without getting main house too warm (we set it to 72). So now my question is, looking at the furnace ID, is there an aftermarket blower that will fit that space and has a higher CFM? Or am I stuck with installing a duct booster? Thanks

 
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Old 11-21-22, 02:57 PM
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You should first verify the furnace size is adequate for the space in your house. If small, consider a new furnace or supplemental heat source in the addition. Second you should check the heat rise listed on the furnace nameplate. The furnace blower speed must be changed to get the stated heat rise. If the addition is still not getting enough heat, try lowering the blower speed to increase heat rise by 5 degrees. If this is not acceptable in the addition but acceptable in the rest of the house, look into a duct blower for the addition duct.
 
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Old 11-21-22, 03:05 PM
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The duct work runs through a crawlspace thats sealed from the basement and is vented to the outside
​​​​​​​Is the duct insulated?
 
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Old 11-21-22, 04:00 PM
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No it is not insulated yet. I plan to insulate the entire addition including the duct work when I have the time. I guess I could ask, is wrapping solid duct easy enough or is it okay to remove and install flexible that comes insulated?

its 110k btu and my home is 2200 sqft.

If I am reading it correctly then the heat rise is "low 55-85"
 
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Old 11-21-22, 05:53 PM
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That has a four speed blower motor. Did you try increasing the speed ?
The heat rise is 55░-85░ degrees over incoming air temperature.

 
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Old 11-21-22, 05:58 PM
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Depending on where you live, 110k btu ought to be plenty...my 75kbtu heats my 2200 square feet in NE ohio easily. Of course a lot depends on insulation levels, etc, but it doesn't seem way undersized.

Insulate the solid duct. Replacing with flex will just further reduce the airflow (a lot). Insulating it is easy if you have reasonable access. That alone may be enough to solve your problem. If the existing duct seams aren't sealed with foil tape or mastic now, do that before insulating. Don't use duct tape to seal the duct.
 
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Old 11-21-22, 07:20 PM
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I don't know how to tell what speed it is on or how to change it. I am assuming it would be swapping a hot wire but which one. I am going to try and insulate the duct this coming weekend. Do you have a preferred wrap suggestion?
 
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Old 11-21-22, 08:52 PM
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Try and find a bargain. Duct wrap is fairly expensive.

Link to manual below. Good to have.
In the diagram.... four speed motor is shown. Yours may be three.
Black motor wire is on cool for high speed blower on cooling.
Blue motor wire is on heat for medium/low blower on heating.
The red and yellow wires are parked and can be used.
Let me know what colors you have and what's on cool and heat.
A picture is good too........ How to insert pictures.



Downloadable manual.
 
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Old 11-22-22, 03:00 PM
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Red and yellow is parked like you said.

 
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Old 11-22-22, 03:48 PM
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Swap the blue and yellow wires and try the heat again.
 
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Old 11-23-22, 07:15 AM
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I swapped the wires but I can't feel a difference. I am wondering if the whole house humidifier is effecting the volume of air. I might just have to install a duct booster after all . thanks for all the help.
 
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Old 11-23-22, 09:45 AM
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Put the wires back the way they were in the picture.
Now swap blue and black and try again.
 
 

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