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  1. #1
    Join Date
    Mar 2007
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    5

    makeup air w/HRV and sealed combustion ?

    I am GC'ing my house and I hired an HVAC company but I have a lot of questions about the way they are doing things. They are nice people, but they seem to really be focusing on quick and cheap, but with my ICF house I want to make sure it's done right. Your guidance and opinions will either put my mind to ease to make me seek out another local pro.


    I have a goodman 95% variable speed 115K BTU furnace and American Aldes 300DD HRV ducted to the basement and main floor. We are about to fire the systems, and the contractors put in the vent in today. They have a 3" furnace exhaust pipe running out, but they said the intake will draw air from the utility room. They also connected a 6" make-up air vent from the outside wall to the return air trunk. Keep in mind my HRV's fresh air port is also connected to the return air vent, and it exhausts from the bathrooms.

    Question 1: Shouldn't the furnace get it's combustion air from outside? I also have a power vent water heater in the mechanical room, but I assumed it would also have pipes to get it's combustion air from the outside.

    Question 2: If the combustion air is taken from the outside, is there any reason to have a makeup air vent connected to the return? It seems almost pointless to have that with an HRV, especially an expensive dual core one if it's just going to draw air thru a 6" hole in the wall.

    Question 3: Should I go back and mastic all of the joints? I've heard it's good to do, but I am busy with other parts of this project and when I brought it up with them it sounded like they either didn't want to do it or would want to charge me a lot.

    pics attached
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  2. #2
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    yes to all 3, its a direct vent furnace, should be hooked up that way in new construction. period laziness is the only excuse.

    The other F/A is for dryers, range hoods, bath fans, ect. Make up air for the house.


    Sealing joints can only help, never hurt.
    You can't fix stupid

  3. #3
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    other than no intake pipe, looks good.

    only thing I see is they bent the plenum up inside out

    I hate seeing the writing on the sheetmetal, I always bend it so clean side is facing out.

    Don't see any cross breaking in it either.
    You can't fix stupid

  4. #4
    Join Date
    Mar 2007
    Posts
    5
    thanks for the really quick advice. For the Makeup air, the furnace in the attic also has a makeup air vent connected from the roof to that return air box. Do you think having just one would be reasonable? There is a gas dryer, but the bath fans are on the HRV and the fireplaces are direct vent. There is no kitchen exhaust at this time, since they accidentally left that off their bid, so I'll either have to find someone else to do it or just hope the microwave's recircuiating hood is good enough.


    I'm not trying to tell these guys how to do their job, but I've already caught one big no-no. They put a 95% furnace in the attic, so now I have the added expense of building a room up there and insulating it.

  5. #5
    Join Date
    Nov 2007
    Location
    Chicago
    Posts
    76
    Question 1: Shouldn't the furnace get it's combustion air from outside? I also have a power vent water heater in the mechanical room, but I assumed it would also have pipes to get it's combustion air from the outside.
    Yes it should. You are paying the guy thousands and he is trying to skimp on a few bucks worth of plastic piping? I wouldn't let him get away with it.

    Question 2: If the combustion air is taken from the outside, is there any reason to have a makeup air vent connected to the return? It seems almost pointless to have that with an HRV, especially an expensive dual core one if it's just going to draw air thru a 6" hole in the wall.
    This is ridiculous. There is no reason for a fresh air intake on the return side if you have a HRV.

    Question 3: Should I go back and mastic all of the joints? I've heard it's good to do, but I am busy with other parts of this project and when I brought it up with them it sounded like they either didn't want to do it or would want to charge me a lot.
    It is commercial energy code to seal all joints. I am not sure about residential, but if you are spending a lot on energy efficient equipment and installation, you don't want to be blowing air out of all the seams.

  6. #6
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    One is probably plenty, but depends on codes, our codes do not allow them to tie into the ductwork anymore they have to come down into a can in the mechanical room now. 1 6" would probably be enough but 2 doesn't hurt but get them to run an intake, or have your plumber finish it for you.
    You can't fix stupid

  7. #7
    Join Date
    Nov 2007
    Location
    Chicago
    Posts
    76
    Quote Originally Posted by bjherron View Post
    I'm not trying to tell these guys how to do their job, but I've already caught one big no-no. They put a 95% furnace in the attic, so now I have the added expense of building a room up there and insulating it.
    Did you tell them to put it in an uninsulated attic? If not, then they should be paying for the mistake.

  8. #8
    Join Date
    Mar 2007
    Posts
    5
    I've been doing good to at least get these guys back out to the job. They are nice enough guys, and I think I got about what I paid for unfortunatly. I'm guessing that they probably get away with this stuff on most of their jobs. I at least had my own manual-j done to make sure everything was sized properly.

    On the makeup air, my biggest reason for wanting to ditch that on the main system is because they have it piped right in the return air next to two bedrooms. If it's cold out (Michigan) and the furnace isn't running inside, I'd think those two rooms might be hard to keep consistantly warm. I don't care as much about the second floor makeup air because it has it's own system and the makeup air comes in much closer to the furnace.


    I'll have them hook up the furnace intake pipe, that's the least they can do. I also want them to move the exhaust one and do a better job, I counted 5 90 degree bends over about 30' of tubing.

  9. #9
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    ICF? just the basement or all the way up? if so whats the square footage? We did an ICF basement to roofline, about 2000 sq ft, installed a 40,000btu 1 1/2 a/c
    You can't fix stupid

  10. #10
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,350
    I think that's the first time I've seen an A/C coil put on backwards.

  11. #11
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    best thing for the make up air is to ask your inspector if it can go. if it isn't needed for code, then rip it out.
    You can't fix stupid

  12. #12
    Join Date
    Mar 2007
    Posts
    5
    the house is about 7000SQ/FT total. The ICF goes to the roof, but the second floor is under a hip roof and stick framed. 2600SQ/FT basement w/ICF, 2600SQ/FT first floor w/ICF, and 1900 SQ/FT 2nd floor stick framed. We are using a 4-ton system for the main two floors, and a 2.5 ton for the 2nd story. It would be less, but there's 37 windows and 8 doors.

    thanks for all of the advice.

    Do you think it will function with the AC coil on that way, or shoud I have them turn it?

  13. #13
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,350
    I wouldn't say it's going to hurt the performace of it in any way, but it's just irregular and not the way it's usually done. I would have them turn it around to face the way the furnace service panels are as it should be. Good luck. See: http://img261.imageshack.us/img261/4...ture014kl3.jpg

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