Mini Split Size Verification

[BeBeep]

I have performed several searches and I believe I have found the correct size mini split system I need for my garage but I wanted to ask for your opinion/verification.

I am located in the Dallas/Fort Worth TX area. My garage has a 9' ceiling & no windows. The dimensions are below in the attached drawing. I came up with 890 SQFT. The garage is insulated, has insulated doors and blow-in fluff type insulation above the ceiling.

I used a online calculator and it appears I need a 33100 BTU unit. Does this sound correct?

Thank you for any comments.

 

[saba007]

How many windows do you have? Good to understand how much sun beams in.

 

[saba007]

Btw according to this you may be over cooling http://www.energystar.gov/?c=roomac.pr_properly_sized

 

[BeBeep]

How many windows do you have? Good to understand how much sun beams in.

Sorry, no windows.

 

[BeBeep]

Btw according to this you may be over cooling http://www.energystar.gov/?c=roomac.pr_properly_sized

I used this calculator with 1.20 Adjustment Factor; http://www.acdirect.com/mitsubishi_learning_center.php?li=2

Which one should be used?

 

[saba007]

I personally tend to trust the vendor calcs less since it is in their best interest to sell us bigger units. If it were me, I'd go with 22-25000, especially since you have no windows and you're well insulated. My 2 cents as a consumer. Hopefully some of the pros will weigh in.

Btw for reference, I have a 12-13k btu window unit at the house cooling 800 sqft right now in 90 degree weather to 68 degrees.

 

[BeBeep]

I personally tend to trust the vendor calcs less since it is in their best interest to sell us bigger units. If it were me, I'd go with 22-25000, especially since you have no windows and you're well insulated. My 2 cents as a consumer. Hopefully some of the pros will weigh in.

Btw for reference, I have a 12-13k btu window unit at the house cooling 800 sqft right now in 90 degree weather to 68 degrees.

I agree with you since so many posts I have read list lesser BTU units versus what the calculator does.

Thank you for your response.

 

[Jackfre]

mini-splits are "net to the space". A Manual J takes into consideration approx 18% duct leakage. I think your 33kbtu looks kind of high. Given that mshp's have no duct leakage, correct for that number. If you figure 33,000 x .82 = 27,000. Personally, I'd put in a 24 kbtu unit and let it work at the peaks when necessary.

 

[JakeKohl]

33k is too much. I've got 18k in my 24x36 in South Carolina and it handles the heat and cool easily (and manages heating in the winter like a champ). I ran a detailed calculation after buying a short term license to HVAC calc that required the input of a lot of variables including the magnetic orientation of the building (sun direction). It said that I needed 11.5K btu (well insulated, 5 windows, 2 entry doors, everything well insulated including garage doors...but I do have a conditioned 2nd story over it so my heat load from the ceiling is non-existent). On a 95 degree day, the 18k will take my space down to 76 in 10 minutes and then it modulates around low speed for the duration. I would say that HVAC calc was very accurate and that my 18kbtu units are a little overkill (but nice because I don't cool it all the time and it's convenient to not have to wait long).

18k would probably suit you just fine...go 24 if you feel like not having any concerns about it with some extra heat coming from the attic that I don't have.

 

[BeBeep]

mini-splits are "net to the space". A Manual J takes into consideration approx 18% duct leakage. I think your 33kbtu looks kind of high. Given that mshp's have no duct leakage, correct for that number. If you figure 33,000 x .82 = 27,000. Personally, I'd put in a 24 kbtu unit and let it work at the peaks when necessary.

Thank You

 

[BeBeep]

33k is too much. I've got 18k in my 24x36 in South Carolina and it handles the heat and cool easily (and manages heating in the winter like a champ). I ran a detailed calculation after buying a short term license to HVAC calc that required the input of a lot of variables including the magnetic orientation of the building (sun direction). It said that I needed 11.5K btu (well insulated, 5 windows, 2 entry doors, everything well insulated including garage doors...but I do have a conditioned 2nd story over it so my heat load from the ceiling is non-existent). On a 95 degree day, the 18k will take my space down to 76 in 10 minutes and then it modulates around low speed for the duration. I would say that HVAC calc was very accurate and that my 18kbtu units are a little overkill (but nice because I don't cool it all the time and it's convenient to not have to wait long).

18k would probably suit you just fine...go 24 if you feel like not having any concerns about it with some extra heat coming from the attic that I don't have.

Thank You

 

[Jackfre]

I like Jake's idea better than mine!

 

[BeBeep]

I like Jake's idea better than mine!

Thank you. That is what I decided to use.

Thank you all for the replies.