HVAC - InspectionNews

Dominic Caronna · #1 (**permalink**) 02-25-2008, 08:00 PM

Is it OK to share the return air compartment of 2 FAG furnaces? Both units have seperate returns, filters, thermostats, and supplies. They are set up to run independently and cool the East and West side of the home. They are next to one another on a raised platform--should there be a panel inthe return compartment inside the platform isolating the return so air can not be pulled from the supply of one unit when it is not in use and vise versa? Could the cage of the off unit turn backwards when the other unit is running? Seems like an issue.
DAC

Jim Luttrall · #2 (**permalink**) 02-25-2008, 08:36 PM

Not an issue in my book. If you put a divider in that platform, the air pressures are still there to do the same thing. YOU might feel better about it, but the effect on the system would be negligible.
If the return plenum is sized correctly there should be enough air to satisfy both units when running and therefore twice as much when one is off. Even pulling air back through the supply vents would not be detrimental.
I would be more concerned with the combustion air, ensuring that there is enough, and that it is seperate from the return air.

Scott Patterson · #3 (**permalink**) 02-26-2008, 09:08 AM

Quote:

Originally Posted by Dominic Caronna

Is it OK to share the return air compartment of 2 FAG furnaces? Both units have seperate returns, filters, thermostats, and supplies. They are set up to run independently and cool the East and West side of the home. They are next to one another on a raised platform--should there be a panel inthe return compartment inside the platform isolating the return so air can not be pulled from the supply of one unit when it is not in use and vise versa? Could the cage of the off unit turn backwards when the other unit is running? Seems like an issue.
DAC

I have never seen this done, and it sounds from a logical point of view as if it might be a problem. When one unit is off and the other is on, unfiltered air will be drawn through the supply registers. This over time will clog the coils on the unit(s). I would also think that if both units are on that one unit will be drawing more air than the other, simply by design or that one unit might have a little more fan speed.

I would call it out for the above reasons.

You might want to call the HVAC manufacturer to see if they could give their blessing on a system like this.