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Thread: HVAC experts

  1. #1
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    HVAC experts

    I called an ac company for a quote to install an HVAC system in my steel shop that's 1500 sq feet and 12ft high. The guy said on the phone it would need a 5 ton unit, but looking at the charts online they say only a 2.5 unit would be needed. Is he thinking the shop won't be insulated as well as a house? I plan on installing whatever the correct R value is needed for zone 1 which is Houston. I've heard companies frequently want to oversize units for some reason and this is a big problem.

  2. #2
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    If they didn't do a heating/cooling load calculation for your specific situation, find another contractor.

    An oversized conventional A/C won't run often enough and long enough to adequately manage humidity, which should be a concern in Houston.

    On the other hand, high end units with two stage or variable output can be oversized with less penalty.
    --I had my patience tested. I'm negative--

  3. #3
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    I'll wait until they actually come out and look.

  4. #4
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    I don't know much about HVAC, but running big motors in my shop sure adds heat that doesn't happen in my house. Maybe that's a reason to oversize?

  5. #5
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    Paul is spot-on...you're be better off with "undersized" than oversized because of the cycling relative to humidity which is your "elephant in the room" in the Houston area. So get quotes from other contractors. I'm going to suggest that in addition to a "conventional" AC unit, you also get quoted on MiniSplit which tend to be a lot more efficient. You may pay a little more up-front, but your energy usage will be a lot more attractive because of the high SEER level that Minispits have that conventional systems don't' come close to.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  6. #6
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    Quote Originally Posted by Jim Becker View Post
    Paul is spot-on...you're be better off with "undersized" than oversized because of the cycling relative to humidity which is your "elephant in the room" in the Houston area. So get quotes from other contractors. I'm going to suggest that in addition to a "conventional" AC unit, you also get quoted on MiniSplit which tend to be a lot more efficient. You may pay a little more up-front, but your energy usage will be a lot more attractive because of the high SEER level that Minispits have that conventional systems don't' come close to.
    I haven't read much about those mini splits where have the unit is outside and the other is is inside, but it sounds like if you don't maintain them frequently they get all messed up and need to have some kind of expensive cleaning done to them. Idk, but like I said I haven't read much about them.

  7. #7
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    Any ac system is going to need frequent cleaning to keep dust out of the fan and evaporator. Maybe add a prefilter. Mini splits can be had with heat pump function for not much more money.
    Bil lD

  8. #8
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    I'm stubborn so I tend to stick with what we've been using for the last 50 plus years. lol

  9. #9
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    Quote Originally Posted by Travis Conner View Post
    I haven't read much about those mini splits where have the unit is outside and the other is is inside, but it sounds like if you don't maintain them frequently they get all messed up and need to have some kind of expensive cleaning done to them. Idk, but like I said I haven't read much about them.
    There is no duct work to clean like with a conventional system, and I find it takes me about 5 minutes to clean the filters on mine which I do about once a month since it's right over my CNC machine in the shop. It takes about the same amount of time that it takes to change the filter on each of our two conventional HVAC systems in the house to maintain my MiniSplit and it's not even been noticeable on our electric bill. But my shop is also well insulated. If we move in a year or two to downsize, if whatever house we buy has an older HVAC system that potentially needs replaced, it's very likely that I'll put in MiniSpilt for that, too, and decommission any conventional system.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  10. #10
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    Quote Originally Posted by Bill Dufour View Post
    Any ac system is going to need frequent cleaning to keep dust out of the fan and evaporator. Maybe add a prefilter. Mini splits can be had with heat pump function for not much more money.
    Bil lD
    MiniSpilts by definition are heat pumps.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  11. #11
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    Travis, a load calc is important but most companies do not do them and also would not know to include all the motor loads. Insulation is the key. The better insulated the smaller the unit can be. I prefer a conventional system with duct work for distribution of the air. As far as cleaning I have a 2 ton split system in my 840 sq. ft. shop and us a 2" pleated filter as a prefilter in the return grill along with a 4" pleated in a filter box at the air handler in the attic. So far in 12 years the blower and coil are still like new. The 2 ton is larger than the load calcs that I did (1.5 ton) but I prefer to keep the shop comfortable with equipment running on a hot day. I live in CA. East of Sacramento. It will get over 100 deg. on occasion. My shop is built like a house. R-13 in 2x4 walls with R-30 in attic. I also have rool up garage door that is 16' x 8' that is insuated at R-5.
    Jim, hate to say but mini splits are not all heat pumps by definition. They come in AC only or HP. We used quite a few for cooling wine rooms in houses. Also I have 35 plus years in service and teaching in the industry so if you have any questions please ask.

  12. #12
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    Looks like my 1500 sq ft house is a 3.5 ton as a comparison. Just a coincidence that my house is the same square footage as the shop. lol I turn the ac up to 80 and it takes about an hour to get the house down to 73 on a 100 degree day when I turn it down for the night if that means anything. I've never had any issues with it not being able to keep up at all. I guess for the shop opening and closing a bay door may need to be taken into consideration too.
    Last edited by Travis Conner; 10-31-2020 at 1:03 AM.

  13. #13
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    Yea, you're only going to want to open the big door if it's absolutely necessary if you are conditioning the space and if you can plan it for the cooler part of the day, that's even better.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  14. #14
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    Sealing around the edges of a big roll-up might be an issue. For the roll-up in my shop, there are large -- like inch-wide -- gaps around the roll-up. If you condition the inside of your shop, that'd be a problem.

  15. #15
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    Quote Originally Posted by Paul F Franklin View Post
    If they didn't do a heating/cooling load calculation for your specific situation, find another contractor.

    An oversized conventional A/C won't run often enough and long enough to adequately manage humidity, which should be a concern in Houston.

    On the other hand, high end units with two stage or variable output can be oversized with less penalty.I a
    I agree with all this, starting with the load calculation. I found an online calculator that gave me a good idea of the sizing before I even started looking for a contractor. The using the calculator may require a bit of research but it took into consideration the volume of the space, floor, type of insulation, losses from windows/doors, etc.

    A good contractor is the key - some eyeball the space and give a high quote and apparently most people fall for it. Don't be afraid to shop around! When replacing the large unit at my house (it's a 3-ton commercial unit) I called three companies, ultimately using the one that came highly recommended by an architect friend. His price, btw, was about 1/3 of the first company I called and 1/2 that of the second. I was so pleased with his attitude and work I had him put another unit in my shop.

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