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Posted by on January 20, 2007, 12:21 am
> Recently replaced my forced air oil furnace with a 5 ton dual speed
> WaterFurnace Envision. My HVAC guy told me the not to worry about my
> ducting as the ECM motor will overcome the lack of duct size.
It doesn't matter eh... ? you better get a new HVAC technician!
> I mainly
> concerned about my return air vents.
>
> Here are some details;
>
> - 2 story house - 2800 sq/ft
> - Near Toronto Ontario
> - Two supply ducts 12"x8" and 12"x7"
> - Two return duct 14"x6" and 12"x8"
> - 18 heat registers feed by 5" dia ducts
> - 4 return air vents 15"x7" (2 up stairs, 2 downstairs)
> - Design heat loss of 63,312 btu/h
> - Heat gain 30,000 btu/h
> - Furnace blower settings - 1st stage CFM=1500, 2nd stage CFM=1950
>
> Quite honesty everything seems to be working fine...... slight noise
> from downstairs return vents, however we're warm. Defiantly much long
> run times over oil.
>
> I've read many times the CFM should be 400 per ton (cooling?)..... I'm
> nowhere close. So I having trouble sleeping at night not know if I my
> ducting is incorrect or I shouldn't worry as the ECM motor overcomes it
> by pushing more air. Also adding to my confusing is the supply duct on
> the furnace measures only 14"x14".
12 x 8 & 12 x 7 with a plenum that's 14 x 14... for a 5 ton unit... Oh MY.
> I'd very much appreciate your thoughts and advice,
> Thanks
>
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