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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 21995
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have a Carrier Model 58MXA100-20 (WeatherMaker 9200) Ultra

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I have a Carrier Model 58MXA100-20 (WeatherMaker 9200) Ultra High Efficiency Gas Furnace. An energy audit by my local utility company indicated that the blower fan was working harder than it should to move the air. The consultant suggested I check for a clogged filter (which i change regularly) or see if one or more of the ducts were collapsed or otherwise clogged.

Upon further inspection of the unit, it appears that the blower motor is situated to pull air from the side of the cabinet that DOES NOT have the cutout for the return ducts. In other words it is pulling air from the closed side of the enclosure.

Is this model's "blower" motor designed to be able to properly function in this manner or could this be contributing to the inefficiency of the air handling function ? The local utility audit indicates that i am using 25-30% more kWh that a similarly equipped home.

The unit has been functioning in this manner since its original installation (new construction) in December of 1998, 12 years.

Thanks very much




This unit achieves the same airflow vs. energy used from either side or the bottom. It cannot pull from the back of the cabinet. Both sides of the housing pull equally even though the motor is on the right side facing.


I would be led more towards undersized duct..either supply or return...or potential plugg ac coil, if equipped.


You can see here the installation instructions per manufacturer.


Customer: replied 5 years ago.
sorry - closed this inadvertantly. Follow up question ok ?




Customer: replied 5 years ago.
I am not very technical so appreciate you bearing with me. So what you are stating is that when you say that "Both sides of the housing pull equally even though the motor is on the right side facing" this means that it doesn't matter where the cutout for the return is located. The "fan" side of the motor does not need to be on the side open to the return ducts ?

Would there be any value in reversing (can that even be done) the motor to have the fan align with the cutout for the return ?


There is no gain by reversing the blower motor...


However....many contractors do not cut the entire allotted space from the side of the furnace.


You may want to have an hvac tech check the system for duct static and balance.


I will say though I have had issue with the energy inspectors not knowing the whole picture.


Example: Here the concern is the draw of the motor....what if I cut an extra return in the other side of the furnace and an extra supply in the top? The motor will now run comfortably...but I have done nothing to use that saved energy to heat/cool home and have actually impeded the system by short cycling the air in and out of the furnace without using duct.


You could gain maximum motor return by unhooking all the duct...but in turn the unit runs longer because of impeded delivery.


My point is...make sure the issue is worth investigating, and then that improvement does not cost efficiency elsewhere.

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