mini split in 90 year old garage remodel

[richdizz]

I'm in the middle of a remodeling my 90 year old 1.5-story garage. I've decided to heat/cool the upstairs apartment with a mini split, but get very inconsent sizing recommendations from calculators and HVAC vendors. Here are the details of the garage:

- Location: Dallas, TX
- Size: 264 sq/ft
- Ceilings: low (shed dormers...see attached picture)
- Windows: 5 (2 South-facing, 2 North-facing, 1 East-facing...all new EnergyStar certified)
- Doors: 1 (to enclosed stairwell without climate control)
- Shade: Very little
- Insulation: Low/Average (R15)

2 vendors have recommended 1.5 ton units and a third said I would be fine with a 1 ton unit. I'm torn between a 1.5 ton 18200btu/20.5 SEER unit or a 1 ton 12000btu/26 SEER unit...thoughts?

 

[JakeKohl]

If they aren't actually running your structure through a J-calc (or using software), they're erring on the safe side of things.

When I chose the split for my garage I bought a 30 day license to HVAC Calc. It said I needed 11 kbtu for my full 2nd floor and 10.5kbtu in my downstairs garage. I ended up adding some safety factor and going with two separate 18kbtu units in each 864 sqft space. They perform marvelously and, if anything, are probably over sized. The online calculators said I needed between 2.5 ton 3 tons for each space.

264 sqft is nothing (assuming you have some reasonable amount of insulation). 1 Ton is probably overkill but should do it.

 

[richdizz]

Thanks for the response Jake...1.5 tons for 264sqft seemed like overkill to me too (even for Texas). Here a picture of the low ceilings:

 

[ShawnJ]

Unrelated - Anyone else getting prompted to login to dallasmtc.com when viewing this thread?

 

[richdizz]

Sorry ShawnJ...login prompt was from the image host...fixed now

 

[JMURiz]

I would also think the 1-ton is more than enough for that space.

 

[purevil115]

I have a 600sqft garage and is cooled with a 9000btu mitsu unit. Your biggest mistake is oversizing. 1 ton for a 300sqft space is way too big. But if its a inverter setup a one ton setup would be fine since itll ramp down when its not needed and also will heat really well being a one ton. But normal cheaper mini splits arent inverter this makes a huge difference in your case.