Sizing and Adding Return Air

[grimbot]

I have a 5-ton A/C system in my attic with two returns. Both filter grills are 16x30. Upstairs return has a 14 inch duct and downstairs has an 18 inch duct tied into a chase in the wall. Is this addequate return air for this system? Also, ducts are tapped directly into furnace in two locations, the bottom and side (horizontal install). Is this an acceptable configuration. I need some base knowledge before speaking to installer about upgrading system. Thanks.

[beenthere]

Post pics of the ducts attached to the furnace.
Your return grilles are small.

[grimbot]

beenthere: Thanks for the response. Attached is a picture of the furnace. The disconnected duct is the 14" and the other is 18".

[beenthere]

About the worst way to attach them.

Should have a plenum attached to the furnace. And then the ducts attached to the plenum.

[dash]

Return grille may be okay,depends on the rest of the return duct system.

What size wall chase is being used?

Connecting the flex directly to the furnace is restrictive,needs a "full-size" cutout at the side and bottom,then go to round,tapered to round is better.

[grimbot]

The wall chase is unfinished (no duct inside wall) but its big. Not sure if chase is the right word...

As far as a new supply plenum... what should I look for when I talk to installers... plenum on the bottom, plenum on the side, both? How big? I can't spend time meeting with these guys without knowing if their solutions are half-baked.

Thanks for your help guys...

[dash]

The wall chase is unfinished (no duct inside wall) but its big. Not sure if chase is the right word...

As far as a new supply plenum... what should I look for when I talk to installers... plenum on the bottom, plenum on the side, both? How big? I can't spend time meeting with these guys without knowing if their solutions are half-baked.

Thanks for your help guys...

New supply plenum,or return?

Best air flow,return both sides,or one side and bottom,for larger furnaces,it's in most mfrs specs to do this.

[grimbot]

Dash - My bad... I meant return plenum...

[tedkidd]

http://lh3.ggpht.com/_1jpVG5c463M/Spy1K_OH5wI/AAAAAAAAWKk/wUkgSctW2FY/s512/scan0046.jpg

side and bottom

[dash]

http://lh3.ggpht.com/_1jpVG5c463M/Spy1K_OH5wI/AAAAAAAAWKk/wUkgSctW2FY/s512/scan0046.jpg

side and bottom

The return drop duct connetion looks a little small,what size furnace/A/C and drop?


Is there any vanes or baffles to separate the side retun from the bottom,or just a "big" box?

[tedkidd]

Not sure dimensions

there are 2 very large media filters behind that door.

We use this for 3.5-5 ton units.

What do you use?