Variable Speed

[cbmechanical]

Is there a situation in which a variable speed furnace or air handler will make the air flow worse.

[Modman]

Yes
When the duct work is so undersized ( or the AC is way oversized) that it blows the ductwork apart! Or the return plenum does not strength breaks in it and the duct work collapses when the filter becomes restricted.

[dash]

I've not seen what Modman is refering to,but even then the air flow is likely better,with variable speed,unless it's as he describes,comimng apart or colapsed.

The variable speed motor will not hold up well if the ducts are way too small.Have your duct systems Static tested by a pro for a definative answer.

[Modman]

I was trying to be humourous. These blowers peak out at 12oo rpm's in restrictive applications. They will stress bad systems worse than conventional PSC equipment

[docholiday]

As I mentioned before, VS systems are an upgrade, not a band-aid for a bad duct system.

[youngoldtech]

Alot of people dont set the variable speed motors, alot of the manufactures set the motor at max, you have to check the staic pressure and set the motor to the right speed. There should be some dip switches or something like them.