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BlueBSH 05-27-2010 11:08 AM

basement causing suction on basment door
I know the title sound wierd..... but here is an explination...

yesterday, had the AC running (it's been almost 90 degrees for 2 days now ugh) and went to go downstairs as I started to pull on the basement entry door (its in the houses foyer) i noticed this suction effect on it... so I stopped and let go and the door pulled itself shut... wierd... pulled it past 6 inches from closed and nothing.... put it about 3 - 4 inches and it slowly closed itself fully.... something is pulling air from the 1st floor down the basement steps and towards the furnance I am assuming... the basment has two cold air returns in it right now (its 2/3rds finished, with the furnance room unfinished)... I have been in the process of sealing the holes in the basement and rim joists so its probably better sealed then it ever was in the past... because there was absoutly no insulation in the basement or rim joists (we dont do that now days in new houses... its all insulated..)

the one room downstairs has three vents in it for air from the supply... all come off 6" branches straight from the supply plenum and go into a drop ceiling tile difuser (the 2'x2' ones that just sit in the grid with a mesh covering)... the bathroom has 1 of these and the game room has a single 6" round baffel (not sure why its a different one but thats how they did it, and just one of them! for a room the same size as the 1st room with three)...

right now about half of them are partly shut to keep some of the cold air upstairs... the basement is freezing!

is this a case of pulling more air then pushing in the basement or is there a problem? the 1st return is littearly right off the furnance... some explaination of this..

the furnance in the furnance room is right against (not littearly) the wall for the center large room in the basement, they ran a 8" duct straight from the boot of the return plenum to the wall (About 1 ft of duct) into a wall joist box they made out of that cardboard like foil faced HVAC board then on the other side of the wall they put a 8x14" grill... which also transfers a TON of noise from the burnance blower motor right into that room... but this return also has the most suction of all the returns in the house....

anyone see any glaring problems with this? or why this is causing the door to pull itself closed?

Anything I can do about the return duct littearly on the other side of the furnace? would it help moving it to the other side of the room as a drop from the return line? the sound is very annoying and I think we are losing most of our return air return from the 1st and 2nd floor to this return... if I cover it up with masking tape the returns upstairs seem to suck a lot more air.....

beenthere 05-27-2010 01:43 PM

Your basement returns are pulling more air, then your supplies are delivering to those rooms.
Your first floor is probably a bit short on return also.

Post pics of the return set up at the plenum, and at that wall.

BlueBSH 06-08-2010 03:21 PM


Originally Posted by beenthere (Post 447631)
Your basement returns are pulling more air, then your supplies are delivering to those rooms.
Your first floor is probably a bit short on return also.

Post pics of the return set up at the plenum, and at that wall.

I have yet to get pics of this, been very busy lately....

I just noticed the other day that the return vents in the 2nd floor are barely sucking anything not even enough to hold a tissue on the wall vent... but the basement vents are sucking as much as a vacume cleaner seems to.... is there any way to balance the return vents? they put no dampers or anything on the returns.. just have the fast and cheap way of doing it with the wall grill... using a joist cavity as a duct and attaching it to a return plenum basically.... even the second floor ones just go through the floor through the 1st floor walls as joist cavity ducts except for one which has a riser duct...

beenthere 06-08-2010 03:26 PM

Its drawing that hard on the basement return because the return path from the second floor is much more restrictive.
Restricting the basement returns will cause more to be pulled from the first and second floor. But, it may not be able to pull enough to make up for the amount its no longer getting from the basement.

Might want to either. Run a new and larger return trunk. or, just add another return to the first floor, so that the basement returns don't pull as much, or can be dampered down.

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