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SportTiger1
LSU Fan
Stonewall, LA
Member since Feb 2007
22745 posts

What size AC do you use for Bonus/Upstairs
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.


LSUtigerME
LSU Fan
Walker, LA
Member since Oct 2012
2496 posts

re: What size AC do you use for Bonus/Upstairs
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.


SportTiger1
LSU Fan
Stonewall, LA
Member since Feb 2007
22745 posts

re: What size AC do you use for Bonus/Upstairs
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


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slinger1317
Houston Astros Fan
Northshore
Member since Sep 2005
4022 posts

re: What size AC do you use for Bonus/Upstairs
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.


lsujro
LSU Fan
BR
Member since Jul 2007
3270 posts

re: What size AC do you use for Bonus/Upstairs
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


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CrawDude
LSU Fan
Baton Rouge
Member since Apr 2019
2238 posts

re: What size AC do you use for Bonus/Upstairs
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.


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ellunchboxo
New Orleans Saints Fan
Gtown
Member since Feb 2009
17373 posts

re: What size AC do you use for Bonus/Upstairs
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.


SportTiger1
LSU Fan
Stonewall, LA
Member since Feb 2007
22745 posts

re: What size AC do you use for Bonus/Upstairs
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


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AEXLSUTIG
LSU Fan
Alexandria, LA
Member since Oct 2011
95 posts

re: What size AC do you use for Bonus/Upstairs
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.


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cave canem
Mississippi St. Fan
pullarius dominus
Member since Oct 2012
11698 posts

re: What size AC do you use for Bonus/Upstairs
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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