# Any Rheem furnace experts? Speed control Q...



## Splinter (Sep 17, 2010)

Is there really much of a difference between high and low fan speeds on a Rheem Criterion II gas furnace? I removed the red (low) and installed the yellow (med) on the fan post and didnt notice much difference. So I stepped it up to the black (hi) on the fan, and there's still no real noticeable difference. I was expecting to hear a rocket sound with the fan on high, but no such luck. 

Is the difference that subtle?


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## beenthere (May 30, 2009)

Depends on the duct work.

How did you size the duct work.


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## Splinter (Sep 17, 2010)

Duct work is ridiculously undersized... It was thrown together by a previous homeowner back in the early 70's... Even with that, I figured I would notice an obvious change in air flow, or sound of the fan at least...

This is only staying one more winter when everything will get replaced with radiant heat, so major upgrades to this system wont happen...


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## beenthere (May 30, 2009)

Depending how undersized the duct work is. It may already be moving all the air it can at the lower speed. So the higher speed won't make a difference.


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