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am i hallucinating or did there used to be a subforum for forced-air furnaces
guess this could also go in the air-con forum but i tend to think of furnaces as furnaces even when the burner is off and it is the evaporator is doin' its thang.
older building with nice main feed and return plenums but haphazard branching and branch sizing and couple large returns not well spaced.
and all the ducts are covered upon leaving the boiler room so don't have a lot of access to think about changing a lot of stuff up easily.
so it does 'fine' for heating but struggles to bring enough load and circulation to comfortably cool the same space. figure this is a typical problem although nothing with forced air is typical to me given i spend the vast majority of my time with forced water.
so it occurred to me in the quick fix department that I might be able to slightly improve circulation by increasing the fan speed. I was busy measuring pulleys but didn't measure the squirrel cage itself which was to my recollection maybe 10 to 12" in diameter and 20" long.
my calculations on the current set up was about 900 rpms at the fan. there was a very little bit of adjustment left on a Maska mvl-34 (3 and 1/4" variable width pulley) so i calculate that I raised the rpms to maybe 975 with that. little bit of improvement. so i figured maybe I'd go for an mvl-40 which takes it up to about 3 and 3/4" outside diameter. and if i did the math right i'd come up a little short of 1080 rpms.
But recalling the false performance notion of simply raising steam pressure to 'fix' a steam system, I thought i'd ask besides my emperical results whether noise or vibration are the worse to fear here. figure there is some logical limit to the rpms desirable for these fans.
know there are systems that operate at much higher air pressures for delivery through smaller tubing, but this is on the bubble so i'm just looking for a slight increment.
i feel like this might accentuate the difference in areas served by larger feeds and well served by returns (which wouldn't be all bad as it would indicate the areas that most need ducting attention when they can handle me making some holes, and i'm working on how to get maybe one additional return installed for the toughest area, but the whole place needs a little more umph on cooling. so i'm pretty much convinced to give it a try. i'm goin' in there. wicked witch or no wicked witch. i just want you to do one thing. talk me out of it ???? or not.