[Fix'n it]

while cleaning my furnace blower, i noticed the area that the cage is in, is about 2" wider than the cage. 1" each end. why is this ? seems to me that the blower would work better if there was narrower gaps.

 

[yuri]

The blower is designed and tested to produce X amount of cfms in the specific furnace it is to be used in with a specific rpm and hp of motor. We are not talking about designing a turbine or centrifugal fan or pump.

 

[Fix'n it]

ok, fair enough. but it seems to me they could make it so it was more efficient.
perhaps there is a safety reason for it.

 

[oldbikes]

I'm not an engineer however I suspect that it takes X amount of Amps to move a cubic foot of air.

If you put an ampprobe on several brands of furnaces a day you will discover that the energy used is very close on all of them.
The biggest difference is the design of the motor not the load it is attached to.

A motor without a run capacitor will typically use several more amps per horse power than a motor with a run cap. Some of the newer variable speed motors are very efficient at converting electrical energy to moving air.

 

[beenthere]

ok, fair enough. but it seems to me they could make it so it was more efficient.
perhaps there is a safety reason for it.

Often 1 blower housing size will serve different models of furnaces that need to move different amounts of air. Its cheaper having only a few blower housing sizes. Then having 10 different sizes. All they have to do is change the height and width of the blower wheel to change the amount of air the blower moves.

So you probably have a blower housing that can move 800 CFM more then the wheel can. And the motor HP is probably smaller also.

 

[yuri]

Efficiency is a buzz word.

Fans are not designed to be "efficient" unless you are talking Industrial sized fans.

Furnaces historically have been as complex as a lawn mower and fan efficiency was not an issue. Furnaces have to be a certain width to accomodate a AC coil and the fan has to be a certain width to fit in and have proper airflow characteristics thru the furnace and coil. Making it smaller and closer to the wheel etc is not plausible. You also have sound considerations and vibration and cost yadayadyada. Blowers wheels get off balance from dirt and motors get end play so if the wheel was close to the housing it will rub.