Basement HVAC

Discussion in 'HVAC Heating & Cooling' started by Al G., Jan 16, 2014.

  1. Al G.

    Al G. New Member

    Messages:
    18
    Location:
    Woodbridge, VA
    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. Dana

    Dana In the trades

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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.
  3. Tom Sawyer

    Tom Sawyer In the Trades

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    Maine
    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.
  4. Al G.

    Al G. New Member

    Messages:
    18
    Location:
    Woodbridge, VA
    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: Jan 16, 2014
  5. Tom Sawyer

    Tom Sawyer In the Trades

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    Location:
    Maine
    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.
  6. Dana

    Dana In the trades

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    Location:
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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.)
  7. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
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    Location:
    Maine
  8. Al G.

    Al G. New Member

    Messages:
    18
    Location:
    Woodbridge, VA
  9. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,047
    Location:
    Maine
    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.
  10. Al G.

    Al G. New Member

    Messages:
    18
    Location:
    Woodbridge, VA
    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. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
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    Location:
    Maine
    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: Jan 17, 2014
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