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What size AC do you use for Bonus/Upstairs

Posted on 7/31/20 at 2:06 pm
Posted by SportTiger1
Stonewall, LA
Member since Feb 2007
28500 posts
Posted on 7/31/20 at 2:06 pm
I am in the early stages of completely my 2 bonus rooms up stairs. My builder framed it pretty well, insulated half of it on accident, and left enough sheetrock for almost all of it.

I have to get an additional HVAC system, and reading stories online give me pause on sizing.

Curious what the board has regarding tonnage/sq ft.

820 sq ft, two large rooms, full bath, and walkin closet.
Posted by LSUtigerME
Walker, LA
Member since Oct 2012
3789 posts
Posted on 7/31/20 at 2:27 pm to
How’s the wall insulation? Knee walls? Direct rafters on a part of the ceiling?

I have a 700+ sqft bonus room over the garage. Floor is open cell foam. Walls are R-19 Batts with knee walls, ceiling is R-30 batts.

I have a 2T Mitsubishi mini split and it does a hell of a job. It’s just one open room, so it’s pretty easy.
Posted by SportTiger1
Stonewall, LA
Member since Feb 2007
28500 posts
Posted on 7/31/20 at 2:34 pm to
18x18 room will not have knee walls and WILL have about 3 ft of attic above it, so i'm not that worried about that one.

but the bonus over the garage will have knee walls and direct rafters. im trying to get the knees to R24ish and the rafters to whatever the hell i can get them to.

floors are 12" sprayed cellulose
Posted by slinger1317
Northshore
Member since Sep 2005
5805 posts
Posted on 7/31/20 at 2:50 pm to
I think you'd be fine with a 1.5 - 2T conventional unit. Upstairs rooms in the South are hard to keep cool, especially if you have attic access in the room.

Have your builder put an AC register about 2/3 of the way up the stairwell if you can. It will help keep you from getting blasted with hot air on your way up the stairs.
Posted by lsujro
north of the wall
Member since Jul 2007
3919 posts
Posted on 7/31/20 at 3:19 pm to
quote:

Have your builder put an AC register about 2/3 of the way up the stairwell if you can. It will help keep you from getting blasted with hot air on your way up the stairs.



this is a great idea. we keep our bonus room warm, but walking up is like a damn sauna
Posted by CrawDude
Baton Rouge
Member since Apr 2019
5264 posts
Posted on 7/31/20 at 3:40 pm to
Do a manual J room by room heat load calculation. Here is a free one for a whole house but you can put the numbers in for the area to be cooled and heated to get you in the ball park. LINK but you can pay a professional to do it for you - would cost about $200-250. Small price to pay to have the HVAC sized properly.

If I had to guess, a relatively new house with insulation at code I suspect 800 sq feet might put you at 1 or 1 1/2 ton (12,000 to 18,000 BTUs). I think the smallest size conventional split HVACs are 1 1/2 tons. Of course you can buy mini-splits at lower BTUs/tonnage.
Posted by ellunchboxo
Gtown
Member since Feb 2009
18781 posts
Posted on 7/31/20 at 4:26 pm to
We have 950 sq ft with two bedrooms, one bath and a “play room” common area and it’s a 2 ton 14 seer.

No issues.
Posted by SportTiger1
Stonewall, LA
Member since Feb 2007
28500 posts
Posted on 7/31/20 at 5:11 pm to
Thanks all. my plans at the moment are for a 2 ton

appreciate the idea on the stairway. ours now is finished, so the cool air stops abruptly at about stair 8
Posted by AEXLSUTIG
Alexandria, LA
Member since Oct 2011
157 posts
Posted on 7/31/20 at 11:16 pm to
2 - 14 x14 bed rooms, full bath and 16 x 24 game room with a 2 1/2 ton unit and fans in all 3 rooms. Very satisfied with my upstairs cooling.
Posted by cave canem
pullarius dominus
Member since Oct 2012
12186 posts
Posted on 8/1/20 at 6:44 am to
Upstairs unit is a 5 ton and struggles from time to time but does well enough overall.

Around 2200 SF upstairs and poorly insulated, may fight that battle one day but not right now.
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