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  1. #1
    I met with my HVAC contractor today to review some questions I had for him (my builder was not there). First, I asked him to bring copies of the Manual J, S and D calculations. He didn't have any...he did them "by hand", so he had nothing to show me. I'll be bringing this up with my builder...

    Two questions (thanks in advance for any input on these):

    1. I have wild heat above my garage, below a bathroom. A qualified friend reccomended that I make sure there is a return in there, or it's useless (like blowing air into a pop bottle). When I asked my HVAC contractor if he was going to put in a return he said 'No, it would just pull insulation back into the furnace.' Should I insist on the return?

    2. My friend also did some calculations based on the first floor square footage, the number of returns and supplies, duct size and equipment size. He said that I'm going to be about 400 CFM short on returns for the first floor. When I asked the HVAC contractor about this, he said that since I am using High-Eff furnace with a direct vent, that bringing in the air from outside makes up for that lack of returns. Is that valid?

    Thanks in advance!
    Rob (Aurora, IL)

  2. #2
    Join Date
    Feb 2005
    Location
    Richmond
    Posts
    480
    Short Answers:

    1. Yes

    2. No

    Long Answers:

    1. Return is needed for proper air circulation. Insist on one located in the cieling and one near the ground.

    2. Load of crap. Direct Vent furnaces have the need the same amount of R/A as a non direct vent unit. Direct Vent simply means that the burners use outdoor air for combustion. This air never comes in contact with the R/A.

  3. #3
    Join Date
    Feb 2006
    Location
    MN
    Posts
    27
    a wild heat for garage?????

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,758
    Do you mean you have trusses above your garage, and a bathroom above the trusses?

    Is your system zoned?

    Did your friend also check the second floor?



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  5. #5
    york_hvac - thanks for the answers. I also got the same answers from rabadger on the "THS HVAC" forum.

    xandair/beenthere - yes, we have a bathroom above the garage. The floor joists of the area that the bathroom is on is framed around, and enclosed (this is the ceiling in the garage). Heat will be provided to that boxed, insulated area to prevent bathroom plumbing from freezing in the winter. I guess its a wild heat for the bathroom plumbing, not really the garage...sorry for the confusion.

    beenthere - I hope you haven't been here It's been a frustrating learning process... My system is zoned, as I'll have two tstats, two furnaces/ACs, but, I believe that it is oversized. Not 'zoned' in the ideal way with dampers, etc using the correct sized equipment and ducts. I'm now going to be going back to my builder and demanding load calcs.

    Thanks, everyone!

  6. #6
    Join Date
    Feb 2006
    Location
    MN
    Posts
    27
    the trap heat does work, but condider the condinsation and bulid accordingly.

  7. #7
    You don't need m-j, m-d only if the t-24 call for it most of the time the m-d's will not work because that is a computer program duct sizing is to large, as for r/a in all rooms yes that would be a better system but if he bid it that way he would of not got the job due to price to high.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    66,758
    Did you get the load calc yet.
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  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,758
    Originally posted by pearce heating & air
    You don't need m-j, m-d only if the t-24 call for it most of the time the m-d's will not work because that is a computer program duct sizing is to large,
    Explain that better.
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  10. #10
    I got the load calc, but it wasn't as detailed as what I was expecting. For each room, it listed Heat BTUs, Cool BTUs, and CFMs. Then, it totaled those numbers up for each floor, and had suggested equipment based on the totals for each floor.

    I was expecting to see the details behind those numbers. What was considered/used in coming up with those numbers. But, it's a start...better then where I was a few days ago.

    I'm meeting with the HVAC contractor and my builder on Monday to review everything.

    Thanks again for everyone's responses!

  11. #11
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    4,850
    aurora

    Do yourself a favor. Click on the Red Tab above and do your own Load/Loss calculation. Compare your #s with his.

  12. #12
    Join Date
    Jan 2004
    Posts
    10
    Originally posted by pearce heating & air
    most of the time the m-d's will not work because that is a computer program duct sizing is to large
    Now, that is an interesting comment. Too large compared to what? Does the program you use allow you to put in the available static pressure and the pressure drop of the fittings and then calculate friction rate based on the total equivalent length of ductwork as drawn in on manual d? If so, and your velocities and equivalent feet for fittings are correct, the program should be dead on the money. If anything, I would be worried that the program would miss an elbow or two because it sees the drawing as flat and doesnt recognize the 90s needed to go over cathedral peaks,etc, and would maybe undersize a little.

    [Edited by jobob on 03-17-2006 at 04:55 PM]

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