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  1. #1

    I'm worried...i think i have too big of unit

    I hope this dosen't violate any rules and if so I apologize and mods please delete.

    But I'm building a garage with an apartment above it. Cellulose insulation, brick vaneer, energy star windows etc in Charlotte, NC. 675 living sq ft upstairs 720 garage.

    I have a buddy (yeah, you know where this is going) who does commercial HVAC and he decided he would save me some money and do the HVAC on my house. Well frankly, I don't think he knows what he is doing. He got a 2 ton york HP from his warehouse. I'm no HVAC person, just a brick mason and 2 tons seems WAY TOO big! there will be 5 8" s and 3 6" supplies upstairs. Against his judgement I want atleast 2 6" vents in the garage to help cool and heat a little when I work down there and also so it doesnt sound like a freight train coming through the vents upstairs.

    Do you Res. guys think he knows what he's doing or am I stuck with some ridiculosly big unit?

  2. #2
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,371
    2 tons for 675 square feet upstairs with your described conditions sounds way too big. If you included the 720 square foot garage that would be a total of 1395 square feet. I too would condition the garage and the upstairs. You should ask him to do a load calculation to determine which size you really need. 2 tons for both sections of the home may be acceptable, but it could be more or less depending on the load calculation. Good luck. I'm not a pro, and I'm sure pros will be along to offer more advice than I can offer.

  3. #3
    this is what i was afraid of. the Tstat would be ubstairs and only 1 return upstairs also. I'm sure
    its against code anyway, but I will NOT put a return in the garage. The garage would only be heated and cooled as the upstairs needed. I've built and done everything by myself. I take pride in going 7-0 on inspections...mech rough is next and not only do I not want to fail, but I wan't something that is going to work...

  4. #4
    Join Date
    Dec 2006
    Location
    Dallas
    Posts
    189
    If you supply... lets say 250 CFM of 800 CFM total to the garage without a return, that air has to go somewhere. You'll have massive infiltration through the garage door due to positive pressure, but then again you may not because your upstairs will have massive negative pressure resulting in horrible air flow.

    Even if you have no return in the garage, any fumes (i.e. gasoline) from the garage will circulate through the door(s) to your living space upstairs, unless you have an airlock for a door.

    If you manage to instal an airtight door in between, you'll have 250 CFM outside air getting sucked in through upstairs infiltration. Actually, you will not, because your air handler will not achieve proper airflow.

    Good luck passing any inspection.

  5. #5
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,665
    if the condensor is not installed yet change to a 1.5 ton

  6. #6
    Join Date
    Oct 2005
    Location
    phoenix az
    Posts
    429
    2 tons is probably ok but have a vent installed in the garage wall to prevent positive pressure and a fresh air vent upstairs to prevent negative pressure these can be louvered to automatically open and close with the pressure change.
    "Do not let what you can't do interfere with what you can do"

    "Do what you can do the best that it can be done and no one will ever know what you can't do"

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,108
    2 Tons is too big.
    He can leave the 2 ton A/H in, and match it to a 1.5 ton outdoor unit.
    York has several matches for that configuration.

    Also putting supplies in the garage from that unit is AGAINST code.
    With the supplied you listed for the apartment, it won't be loud.

    If you want the garage conditioned, install a unit just for it!
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  8. #8
    Join Date
    Apr 2005
    Location
    new jersey
    Posts
    752
    what are the codes for returns in a garage?

  9. #9
    Join Date
    Sep 2003
    Location
    McKinney, TX
    Posts
    470
    2 tons may be just fine. I am not sure about the climate in NC though, so I couldnt tell you. Why did you let your buddy do it if you were going to question everything. Maybe he knows what he is doing.

  10. #10
    Join Date
    Apr 2004
    Posts
    7,680
    Quote Originally Posted by coolmen View Post
    what are the codes for returns in a garage?
    Returns or supplies, either one is against code... The unit's fan will shut off on occasion.

    I like how the OP said his buddy decided to save him some money rather than "I hired my buddy because I knew he would give me a lower price"

  11. #11
    Join Date
    Mar 2005
    Posts
    132

    2 ton is ok

    i am told that almost no one makes a 1.5 ton anymore . two ton is about as small as you can get. so at any rate were talking extra 200 cfm. no problem ac ing the garage with a vent in the supply plenum that can be opened when desired and blow cold air in the garage. NO return though , we don't want to return air out of the garage. supply air only will put garage in a positive pressure and force excesss air out the cracks to exterior. yes the upstaires will fall into a negative pressure for a while but not usually a problem unless you forget to close the vent when your done. The second floor with an unconditioned lower floor may even need a two ton, not enough diff to get your panties in a wad.if your concerned about air noise upstairs then add more outlets and diffuse the air quieter. maybe four outlets instead of two. Don't forget that aprilair filter .

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,108
    1.5 tons is still a common size heat pump. And York does make them.
    He posted 5 - 8" and 3 - 6" supplies, thats enough that he doesn't need 2 more.

    Running a supply to the garage is STILL against code weather you have a return or not.

    1 ton per 337 sq ft is most likely a tad over sized.
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  13. #13
    Join Date
    Dec 2006
    Posts
    32
    Just curious. Would a multiple zoned mini-split unit meet code in this application? Since there is no mixing of air between garage and apartment, I see no apparent danger.

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