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Thread: Basement HVAC

  1. #1
    DIY Junior Member Al G.'s Avatar
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    Default Basement HVAC

    I've had two well-known HVAC contractors quote installing ducts for my basement finishing project. I have a hybrid heat pump/propane furnace for heating and cooling. Both contractors looked over the job site, looked at the manufacturer labels on the equipment and proceeded to sketch out their solution. They did no flow measurements or calculations. They came up with entirely different numbers and locations of registers as well as duct sizes. They also had completely different answers on combustion air requirements. I don't have confidence in either of them.

    I know this is something that needs to be done correctly or it will cause problems with the rest of the house. I'm paying them to get it right. I could have come up with what they've given me so far on my own. Maybe it would work, maybe it wouldn't. I don't want that.

    What should I be looking for in their proposals? What questions should I be asking?

  2. #2
    In the trades Dana's Avatar
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    Ideally you'd see from the get-go is a "Manual-J" heat & cooling load calculation, and a Manual-D compliant duct design for supporting those loads. Most commercially available load calculators such as Wrightsoft use Manual-J methods. But that's almost never going to happen for just extending a zone. If they can't come up with numbers for at least a HEATING load, they're just taking a wild stab, probably oversizing the ducts "just to be sure", which won't deliver stable/comfortable basement temperatures.

    Being largely below-grade, basements have very different heat loss characteristics than above grade zones, and often little or no sensible-cooling load coupled with a higher latent load from groundwater moisture diffusing in through the foundation and slab. If it's a fairly open space you may be better off with a 3/4 ton mini-split making the basement it's own zone, rather than marrying it to the first floor zone, or adding it as a separate zone for the main heat pump.

    You can do your own I=B=R methods for calculating the heat load, if you know the U-factors of the windows & doors, and the construction/insulation stackups.

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    In the Trades Tom Sawyer's Avatar
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    When I do a heat quote and design I almost never give that information to the customer. The problem with giving it to the customer is that they will in turn give it to everyone else that quotes the job and I'll be damned if I'm going to spend several hours doing a heat loss and duct calculations for free or for a job I may not get. That you have differing opinions is normal too because there are always a few different ways to accomplish the goal. Unless you personally engineer and spec the job you will get exactly what you got. As for your confidence in the people doing the quote, that is mostly your own fault.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member Al G.'s Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    As for your confidence in the people doing the quote, that is mostly your own fault.
    How is this my own fault? I selected two reputable contractors in my area. It's not like I found some guy on the street and asked for a quote.

    Also, I'm not asking them to share any calculations. Both of them stood there in the basement with me and sketched out register locations, duct sizes and return locations. They only thing they didn't give me on the spot was the price. The written quote had exactly what they had sketched so I highly doubt they did any calculations after the fact.

    I'm also being very careful here not to ask for a solution or how to calculate one. I expect to pay for that. I'm just looking for advice on how to be sure I'm working with someone who is taking the right approach.
    Last edited by Al G.; 01-16-2014 at 09:45 AM.

  5. #5
    In the Trades Tom Sawyer's Avatar
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    Ask around, contact the BBB, ask for names of customers. How long have they been in business? If I had to bet, I'd bet that both are experienced and skilled at their trade.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    In the trades Dana's Avatar
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    If all they did was eyeball the nameplate on the equipment and start sketching the "solution", there is clearly no load calculations going on.

    Cook yourself up an I=B=R spreadsheet heat load calc, and tell THEM what the heat load is. It won't be as clean or accurate as a Manual-J, but it sure beats a WAG, which is what the two practitioners seem to be all about. Unless it's a walk-out basement that faces due west with a lot of windows and no shade factors, it's not going to much matter what the cooling load is.

    If it's not a walk out basement and this project is for duct-work only, not a zone with it's own thermostat you'll probably be pretty cold down there during the peak cooling days no matter what, and during the heating season it could vary between too-cool and too warm- you can't really balance it. With a well-insulated basement just a tiny duct with a register you can turn off would let you do the temperature adjustment to suit, but closing down the supply register unbalances the ducts, which increases outdoor infiltration rates (always), increasing energy use. (The magnitude of that penalty depends on how tight your house is.)

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    In the Trades Tom Sawyer's Avatar
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    [QUOTE=Al G.;405816]How is this my own fault? I selected two reputable contractors in my area. It's not like I found some guy on the street and asked for a quote.

    Well are they are aren't they?

    I doubt one in 50 would run a manual J for adding a couple registers to the basement. I sure as hell wouldn't bother. All they needed was the make and model of the equipment. From there they can determine the maximum CFM
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  8. #8
    DIY Junior Member Al G.'s Avatar
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    [QUOTE=Tom Sawyer;405827]
    Quote Originally Posted by Al G. View Post
    How is this my own fault? I selected two reputable contractors in my area. It's not like I found some guy on the street and asked for a quote.

    Well are they are aren't they?

    I doubt one in 50 would run a manual J for adding a couple registers to the basement. I sure as hell wouldn't bother. All they needed was the make and model of the equipment. From there they can determine the maximum CFM
    I'll change reputable to large, well-established businesses with high ratings in the local business guide. I assumed they were reputable. I came here with a question about what I should be looking for in their approach to a design. Even here I have conflicting responses on whether a calculation is needed or not. One of them decided on 6 registers and 1 return. The other decided on 7 registers and 2 returns. The locations were entirely different. One of them said I needed a fresh air inlet and the other didn't. I checked with the county and did my own calculations that said it wasn't needed. So I question whether one contractor doesn't know what he's doing or was trying to add on unnecessary work. Like I said, even before either of them came I had in mind a solution that is close to either one. Maybe I should save myself a couple thousand dollars and do it on my own. I'm sure that will generate even more comments about not using a professional.

  9. #9
    In the Trades Tom Sawyer's Avatar
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    You are the one that said they were reputable and I'd bet they both are. The difference between one register, either supply or return ain't going to make a difference. There are several ways to accomplish the same job. If you get three quotes, you will also get three different prices and three different ways of skinning your cat, but I'd also bet that both of the contractors you called will give you value for your dollar spent. As for doing it yourself? Why not. Learn to be a tin knocker, learn how to properly size ductwork and how to install it to the mechanical code and sure, you can save a bit of money. That neither contractor spent three hours drawing up plans and doing a heat loss means virtually nothing. They didn't do it because chances are they have handled situations like yours many dozens of times over the years. Contrary to what some may tell you, an experienced contractor can indeed tell you pretty close to exactly what you need because he's been there, done that.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  10. #10
    DIY Junior Member Al G.'s Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    That neither contractor spent three hours drawing up plans and doing a heat loss means virtually nothing. They didn't do it because chances are they have handled situations like yours many dozens of times over the years. Contrary to what some may tell you, an experienced contractor can indeed tell you pretty close to exactly what you need because he's been there, done that.
    Why didn't you just say that in your first response? I came here and asked what kind of effort I should expect to see in preparing a quote for my job. I'm not experienced in this area and wanted to know if quick solutions such as those two contractors proposed were the industry norm for this type of job. I thought this forum was a place this kind of question could be asked.

  11. #11
    In the Trades Tom Sawyer's Avatar
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    It is the place to ask but remember that this is a diy site so anybody can respond to your questions. We have homeowners, engineers, contractors and service tech all answering questions. I tend to approach the problem from a practical point of view, having been in the business for almost 40 years now. There is a line between cost and practicality. You do a complete manual J on the house and the 1st thing you are going to find is that your current equipment is probably 50% oversized for both heating and cooling. You will, if you dig deep enough, also probably find that your existing ductwork could have been improved upon but, do you really want to go to the expense of tearing everything out and starting over? Even if you do, do you have the money to tear it all out and start over? Most folks will say hell no. You can spend a whole lot of time and money just to save a few dollars.
    Last edited by Tom Sawyer; 01-17-2014 at 08:37 AM.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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