Return air issues

[mattmctree]

I was at a customer's house and they were complaining of doors closing when the furnace or air conditioning was on. It is a bungalow and the only return air is a large grill in the floor.  They don't want to do a large project and do a bunch of new duct work. I was thinking that I could put a grill in the return air boot and provide more return air. Would this be sufficient

[Admin]

It definitely sounds like you need more return air, or lower the fan speed if the AC size permits.

Be careful where you install a return air opening.  Download the Gas and Building Codes regarding return air here,

http://www.hvactechgroup.com/files/Return%20Air%20Codes.pdf

[mattmctree]

I am dual piping the system and the water heater is electric.  The basement is completely open . As far as I can tell from the above codes I would be ok install a grill on the return drop. Would I be correct in assuming so

[Admin]

Code wise you're likely okay.  I bet there's something in the SMAC duct design manual that touches on this though...

I would say it's not good practice to install a return air opening so close to the furnace blower.  The fan could take all the return air it needs from the new opening and the other return air could become useless.  In your case you only have one return air anyway.  Code requires one return air per floor, so the basement should have one.  Are you able to add a takeoff further away from the furnace, on the trunk line?

And you mentioned installing a 2 pipe system.  Does that mean the existing system is using combustion air from inside?  Maybe this is a negative air issue.  I'm second guessing myself if adding the basement return air would help or only make the door close faster.  I know having a return air in every bedroom would be preferable.

[Porcupinepuffer]

I would also agree with trying to put the grill somewhere on the trunk line at least a certain distance away from the return drop. I also believe the furnace blower will suck the air too easily at a location too close to the furnace. I can't recall anything from the smacna duct construction manual. But they do have several other manuals that may cover it.  I do know too close a return air can allow unwanted noise from the blower. I'd do some air flow tests and check static pressures for any signs of restriction. But if there isn't any return in the basement, it should have one.