Hotblast CFM Question for Return

[Racerboy832]

I have the US Stove 1537G (Same as 1557 M). It has 2 8" outlet holes. 2) 550CFM Blowers. I just am about to install a Cold Air return box but I need to size up the return. If the blowers are capable of pushing 1100 CFM and each 8" hole is capable of Flowing 200CFM (Found Online). Then Am I wasting electricity trying to pump 1100 CFM through holes that will only let 400cfm through. Does the return have to be sized to the same as the output of the 8" holes or 1100CFM blowers. The basement air is too cold to suck out of there to make it efficent.

 

[smokinj]

I have the US Stove 1537G (Same as 1557 M). It has 2 8" outlet holes. 2) 550CFM Blowers. I just am about to install a Cold Air return box but I need to size up the return. If the blowers are capable of pushing 1100 CFM and each 8" hole is capable of Flowing 200CFM (Found Online). Then Am I wasting electricity trying to pump 1100 CFM through holes that will only let 400cfm through. Does the return have to be sized to the same as the output of the 8" holes or 1100CFM blowers. The basement air is too cold to suck out of there to make it efficent.

I have 2 10 in. as return

 

[jdew1920]

I'm sure you will move more than 200 cfm through each 8" duct. When they give ratings like that it's not to say that you couldn't get more flow through - it just depends on the velocity of the air flow.

Anyways you always want to have at the minimum the same amount of return air cross sectional area as you do in supply. So an 8" duct is about 50 sq in - two of them is roughly 100 sq in. So you need at least 100 sq in on the return side. I think it's easier to run 1 larger duct that two smaller ones. A 10" round duct will give you about 80 sq in, 12 round about 120 in sq. Of course nothing says you can use rectangular duct either - an 8 x14 return would give you 112 sq in.

 

[Racerboy832]

I am kinda tight on space. Would 1 10" be ok to use for the return?

 

[smokinj]

you need at least 2- 8 in. You have any pic's of it? May be easier to run square