Question about Goodman GDS80904BNA Open Flame Heater

# Need the cubic inches for the return air duct

I am setting up return air for a new goodman furnace. There will be two return air ducts that travel through the house. I don't know the cubic inches these two ducts need to be. The two return air ducts will come together at a 10 inch by 20 inch main return air duct at the furnace. The duct work has to travel through the house and I am not looking for the length, but the cubic inches of the end of the two ducts combined. the furnace I have is a Goodman model number GMH80904BN. The product number below has the letter "A" at the end of it and mine does not.

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For proper minimum opening you need to do duct calculation. This is not a typical math equation for the typical homeowner. And unfortunately alot of contractors do not take the time to calculate this.
If you insist on doing this yourself...... I would recommend the largest opening that a common filter will fit. probably 20" by 25". Going to big on a return air will never hurt. But going to small will.
20" x 25" will work safely 95% of the time. But... If you are running airconditioning that is 5 tons in size, you will need the design a return air system that will feed from BOTH sides of the furnace.

If you are just sizing the trunk line you should use a ductulator to calculate the minimum size. A good rule of thumb would be to size the "return air" trunk 1 - 1 1/2 times the size of the supply trunk line.

Posted on Mar 08, 2009

Hi,
a 6ya Repairman can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repair professionals here in the US.
Goodluck!

Posted on Jan 02, 2017

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