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  1. #1
    Join Date
    Jul 2005
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    Greetings from Texas. Let me get to the point. I have a 24x30 metal building on a slab used for a backyard wood working shop. Inside is all open floor space.Walls are covered with sheetrock with R11 insulation. Ceiling is R19 with sheetrock. I have just recently added on what I will call a lean-to on the back side of this building. The new part measures 14'x30 feet.I had to construct it in a certain way to have enough ceiling heigh which is 90" from floor to ceiling. The roof of the lean to is made with purlins, meaning a 14' 2x6 every 4 feet followed by 2x6s every 2 feet OC in between the the 14' boards. I have no attic space in this new lean to. Metal roof is screwed to top of 2x6s and sheetrock will be screwed to the ceiling. NOW heres what I would like to know. I have 3 different air/heat contractors coming next week to give me bids on this job but it would ease my mind knowing some key points. Let me number the questions for anyone nice enough to render an opinion.

    1. I will put CH/A in the entire building, main part and lean to. Is is correct saying 1 ton per 500 sq ft is sufficient?

    2. I can see how they will run the duct work in the main building because it has an attic space (roof is a 3/12 pitch) but how will they get ductwork back to the new lean to? In this lean to its 3 rooms, a 14x14, a 8x8 and a 8x14 which will need ducts in each. But i have no attic space, just the thickness of a 2x6. Will this be enough room to put small duct work in?

    3. Code says in this area a supporting member board can be bored or cut 1/3. Thats basically less than 2" you can bore a hole into. Will a less than 2" duct provide enough air/heat to these rooms. Looks to me round ductwork is out in the lean to, looks like it would have to be somesort of an over shape or retangle, but still seems like small duct to me. Am I wrong or will it provide enough air/heat?

    4.I have around $3000 to $3500 budgeted for this air/heat install from a licensed reputable contractor. Of course if I come in under this figure all the good. Am I in the ball park in my figures? Includes ductwork and 2.5 to 3 ton unit with 10kw elec heat. Brand is unimportant to me but I would go for longest warranty.

    My apologies for being so long winded. I was just curious about all this before the ac people come next week for bids. I am in a very rural part of Texas and the people I have called will be driving a 50 mile one way trip.

    Appreciate any replies, feel free to email me direct of post on board. Thanks again.

  2. #2
    Join Date
    Aug 2004
    North Richland Hills, Texas
    Post Likes
    The load on that building probably needs to be done like a commercial load calc.

    Depending on what all kinds of equipment you have in there, and what kind of temperatures you want to maintain, I would say that 3 tons would likely be the minimum. Especially with steel siding, the heat load is going to be higher than with normal residential construction, then there are the internal heat gains from your lighting and equipment.

    As far as ductwork for the added on portion of the building, without seeing it, I can't say much.

    Bluntly, you should have involved an HVAC contractor from the beginning, rather than waiting untill after it is all done. It is probably going to cost you anywhere from 25-100% more now than if you had done the HVAC during construction.

    $3,000 to $3,500 for a 3+ ton system and ductwork is very low if you want anything resembling a quality install, especially considdering you have special ductowork issues and the sheetrock and insulation are already in...

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