texasmax
10-28-2008, 09:19 PM
All-
Recently had a duct blaster test done, and wouldn't you know it, we couldn't even get a reading. I'm thinking (as well as the tech) that the return air setup is the culprit- all return grills are at the floor and go up through wall cavities between the studs. Single-story 3,000 sqft home with all the business in the attic. There are no hand-detectable leaks (supply-side, air handler, or return side, though never did a smoke test on the return side), and all of the boot-to-sheetrock conections have been sealed with mastic. All-new equipment and flex duct 4 years ago that mates to original sheet metal boots, installers masticed all connections.
There are 14 return grilles, a few of them share a cavity and duct (the grilles are in different rooms that share a wall). I've got 7 ducts that meet at the return plenum- 6 from the close side of the house, and an 18-inch round that triangles out to the return ducts from the far side of the house.
So, two questions- based on the above logic, is it a safe assumption that the returns are the cuplrit? Question two- company would like to block off all the existing returns at the grilles and boots, and put in just 4-6 (need to finalize plans here) larger returns in the ceiling (all supplies are in the ceiling), re-usign duct where sizes are appropriate. For 3,000 sqft, is 4-6 returns enough (so long as the grille and duct sizes can and handle the flow)? Found on one of udarrell's pages that I'll need 200 sqins of grille area per ton, so for my 5 tons, I'll need 1,000 sqin, meaning if we did 5 grilles, a 10x20 incher would do it (need to re-check udarrell's page if I'm confusing my grille area vs. free area).
Also, thought I'd post a pic of the current return plenum- the techs got a good kick out of it (apparently 7 is too many)- maybe you will too.
Recently had a duct blaster test done, and wouldn't you know it, we couldn't even get a reading. I'm thinking (as well as the tech) that the return air setup is the culprit- all return grills are at the floor and go up through wall cavities between the studs. Single-story 3,000 sqft home with all the business in the attic. There are no hand-detectable leaks (supply-side, air handler, or return side, though never did a smoke test on the return side), and all of the boot-to-sheetrock conections have been sealed with mastic. All-new equipment and flex duct 4 years ago that mates to original sheet metal boots, installers masticed all connections.
There are 14 return grilles, a few of them share a cavity and duct (the grilles are in different rooms that share a wall). I've got 7 ducts that meet at the return plenum- 6 from the close side of the house, and an 18-inch round that triangles out to the return ducts from the far side of the house.
So, two questions- based on the above logic, is it a safe assumption that the returns are the cuplrit? Question two- company would like to block off all the existing returns at the grilles and boots, and put in just 4-6 (need to finalize plans here) larger returns in the ceiling (all supplies are in the ceiling), re-usign duct where sizes are appropriate. For 3,000 sqft, is 4-6 returns enough (so long as the grille and duct sizes can and handle the flow)? Found on one of udarrell's pages that I'll need 200 sqins of grille area per ton, so for my 5 tons, I'll need 1,000 sqin, meaning if we did 5 grilles, a 10x20 incher would do it (need to re-check udarrell's page if I'm confusing my grille area vs. free area).
Also, thought I'd post a pic of the current return plenum- the techs got a good kick out of it (apparently 7 is too many)- maybe you will too.