I am building a new home in western NC (Asheville area) and my question is regarding how much ac (tonnage) and how many ac units I should plan for. The house is approx 3800 sq ft and is one level. Also, what is the best product to use?
HVAC question for new home construction
CB123
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The builder/contractor needs to do a manual J calculation. In addition to a manual D for duct design. Unfortunately many builders hire the cheapest contractor they can find to throw equipment in.
Brand name doesn’t matter much. The skill of the installer matters much more.
That’s a very humid area. Make sure it’s sized correctly for proper humidity control.
What will be used? Heat pump? Gas furnace? Propane? Natural gas? Geo?
Brand name doesn’t matter much. The skill of the installer matters much more.
That’s a very humid area. Make sure it’s sized correctly for proper humidity control.
What will be used? Heat pump? Gas furnace? Propane? Natural gas? Geo?
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One unit should do it.
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Thanks, I read somewhere that you need about one ton for every 600 sq ft as a guide, does that sound about right? As far as what type (Heat pump? Gas furnace? Propane? Natural gas?), I am not sure what works best for this area but we have natural gas available. I don't know NC very well, I live in Fl and this is a vacation home.
No, there isn’t a rule of thumb as far as BTU per square foot. That is an antiquated way of sizing that shouldn’t be used.
A room by room manual J needs to be accurately done by the installer. To determine system size and design the ductwork.
A room by room manual J needs to be accurately done by the installer. To determine system size and design the ductwork.
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You should get local energy cost per delivered unit including all charges, post and we can tell what makes sense.
Climate factors into this.
A heatpump may make sense when getting a/c anyway, either backed up with electric or in a dual fuel setup (furnace takes over when heatpump can't keep up)
A room by room load calculation is an absolute must.
It's used to design the duct system off of, not just to size equipment -> how much heating/cooling each room needs.
You may be surprised and a load calc for the whole house may come out to < 80k of heat and 3 to 4 tons of cooling instead of 5 to 6 tons and 100-120k btu.
Rules of thumb are mostly useless. New homes are far more energy efficient than most existing.
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I see that this is more complicated than I thought. In the builders' bid he included an estimate of $22,000 for the HVAC (including one 4 ton trane unit). I was trying to figure out if this was going to be a problem for the budget for a house this size, 3800 sq ft.
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Zoning is a can of worms that should not be opened unless really justified.
Basement may be cold during the solder seasons on one system with single zone.
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4 tons for 3800 sf sounds too small, but the installer needs to run proper calcs. I would have 2 separate units, one for the bedrooms and one for the living areas. You may find it advantageous to have different set points at night.
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When the duct system is properly designed and balanced, zoning is largely unnecessary especially on a single story house.
It's beneficial when you have 3 above ground stories on one system and or addition/area of the house with radically different type load. (lets say, far more exposed surface area relative to volume)
Your basement may be cold at certain times of the year on one system, but that can be fixed with some supplemental heat down there (gas fireplace or otherwise), and minimized to begin with with good full height wall insulation.
Zoning, oversizing, multiple systems per house are often just patches for poor design, installation, commissioning/setup. The patches can make matters worse.
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OP: at the very very least, fill out that site.
Whoever was responsible for getting drawings done up for your house, should have also had a hvac designer also design the system to go with it. (that's along side the electrical and plumbing drawings.) If you haven't had the hvac designed yet, hire a designer /engineer to do it. It really will be worth it. The only restriction I'd put on them is not to use the attic space for ductwork.
Cheers!
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I think the rule is you only need two units if you have a multi story house. 3800sq ft is a very large single story home. I think 5 ton sounds about right. I used the cutout above to make my estimate. It's free of charge. On a serious note. Since you live in a warm/hot humid climate. Make sure your duct work is oversized. That is more important than the size of your cooling unit. But I think 5 ton is what you should have.
Totally agree with the guy who said it doesn't matter what equipment you buy but who is installing it. That can be good or very bad.
Totally agree with the guy who said it doesn't matter what equipment you buy but who is installing it. That can be good or very bad.
Fortunately, that is a problem the OP won't have.
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oops.
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