How many BTU's to heat/cool a garage? | FerrariChat

How many BTU's to heat/cool a garage?

Discussion in 'Technical Q&A' started by nathandarby67, Mar 25, 2012.

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  1. nathandarby67

    nathandarby67 F1 Veteran
    Owner

    Feb 1, 2005
    8,349
    Mississippi
    Full Name:
    Nathan
    #1 nathandarby67, Mar 25, 2012
    I am in the middle of insulating my garage to make it more comfortable to work in. OK, truth be told, I am just trying to remove one of the many excuses I have come up with to procrastinate on some car projects I have that need doing.

    Anyway, I decided to go ahead and make it a really nice space capable of doing Real Work. Bought a bunch of cool red steel wall cabinets, tool chests, stainless workbenches, wired for a bunch of 110 outlets, 6/3 wired for 50A 220V service, etc. etc. So, I want to make it nice. I don't plan on keeping it at 72 degrees 24/7, but would like to keep it semi comfortable at all times, and have the ability to crank it up and get it nice and cool in the summer and warm in the winter when out there working.

    I plan on installing a mini split heat/AC unit. Garage is standard 2 car size (21x21), detached from house. It has a 9 foot ceiling, but I was planning on using spray foam insulation on the underside of the roof so the attic storage would be somewhat climate controlled. Walls are 2x4 with R13 insulation. I bought a foam panel insulation kit for the aluminum garage door, not sure of its R value. Oh, I live in south Mississippi, so while the winters are not bad at all, it gets god-awful HOT in summer. I have seen anything from 10K to 20K BTU's recommended for a space like this. I figured a few folks here may have some real world experience in this regard and could lend some advice. I tend to over-engineer and over-build things, so my gut tells me to just buy a big honking system and let it blow. But, I know you can run into humidity and condensation problems along with efficiency problems with too big a unit, so I want to get it right.
     
  2. deeprivergarage

    deeprivergarage Formula Junior
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    Oct 3, 2009
    560
    S of Fort Worth
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    Jerry
    #2 deeprivergarage, Mar 25, 2012
    600 square feet per ton (12,000 btu) of A/C is in the average, but open to argument I am sure depending on the structure. A 1 ton A/c unit should be more than adequate, but note you are right, more A/C is not necessarily better, because of the humidity control issue. The unit can lower the temperature quick, but needs to run for a sufficient time to remove/lower the humidity.

    Check the internet for free A/C load calculators. Then are several calculators online that you can use for your specific needs.

    A window type heat/cool unit would also work for great for 400-500 square feet.

    Sounds like a super plan for a garage. Lucky you.

    DRG
     
  3. fastradio

    fastradio F1 Rookie
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    Apr 26, 2006
    3,664
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    David Feinberg
    #3 fastradio, Mar 25, 2012
    Here's what we used to do the calculations. A web search on "Manual J Load Calculations" will give you the info.
     
  4. rmorse

    rmorse Rookie

    Oct 3, 2011
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    Castle Rock, CO
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    Robert Morse
    #4 rmorse, Mar 25, 2012
    If the main garage doors are frequently opened, you might want to consider putting some kind of PVC strip door on the other side of the garage door. During hot summers it might keep the garage cooler when you pull cars in and out.
     
  5. moysiuan

    moysiuan F1 Rookie
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    Nov 1, 2005
    3,645
    Canada
    #5 moysiuan, Mar 25, 2012
    I have an overengineered garage of similar size, about 20 feet wide, 32 feet long but with tall 16 foot vaulted ceiling, foam insulated walls ceilings, garage insulated doors, laminated double glass windows, etc. The insulation has a huge impact on energy efficiency. I have a split mitsubishi heat pump/air conditioner PUZ-HA36nha2 with a ceiling mount evaporator unit. Overkill for you as it's designed for very low temperatures best pump operation. Works phenomenally well, really quiet, rehearsal or cools within minutes of the garage door being opened. I could have gone with the 24 unit, but the low temperatures model was at the larger size, and I have occasionally extreme cold temperatures delta to contend with, so I went for the unit noted.

    My auto hobby is so much more pleasant with the temp control, I had such lousy workshop garages most of my life, so overkill now made sense to me.
     
  6. fletch62

    fletch62 Formula Junior

    Mar 8, 2004
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    Fairhope, AL
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    Larry Fletcher
    #6 fletch62, Mar 28, 2012
    I am in south Alabama and I use a mini split unit in my shop 1000 sq ft, 9' height 24k btu works good. I would think 12K would work for you.

    Larry Fletcher
    www.cisflowtech.com
     
  7. Futureman

    Futureman Formula 3

    May 16, 2007
    2,024
    #7 Futureman, Mar 29, 2012
    Sorry to hijack, but Larry, can you recommend a CIS expert in Huntsville?
     

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