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  1. #1
    Join Date
    Mar 2006
    Posts
    92
    This forum is great, the knowledge here is unbelievable!

    At this time I have a 60k BTU furance that serves my basement.

    We're replacing the old 80% for the 1st floor on a few weeks with a a new 90% high efficiency furnace.

    Presently the 60k btu 90+ that is in the basement venting goes from 2" in the basement (from the furnace) and is upsized ahortly thereafter beacuse of the the length of the run (per the table) to a 3" and runs up inside the wall and up into the attic, the 3" pvc runs up in the attic and out through the roof. I t may be upsized again to 4" before but I can't remember, regardless the guy that originally did it knew what he was doing.

    (Originally we had it tun out the wall but the exhaust all over the window was a nuicance so we had it changed)

    Anyway , the new furnace will be in the basement - Can I run the PVC right from the furnace, it would make a perfect 90 out of the furnace and then run straight up inside the wall (or empty cavity) and then pop out in the attic,

    Question is this - can it be tied into the the 3" ( or 4")of the 60k btu (that serves only the basement) T'd into the same PVC exhauust as the new 80k BTU 90% furnace (that will serve first floor) of our Ranch, the T would be in the attic and this way I could have one roof penetration?

    Rather than poking another hole in the roof could I just upsize the exisitng 3" penetration to a 4", 5" or 6"?

    Just wondering...



  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,184
    Poke another hole

  3. #3
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,743
    poke another hole. pressure switch safeties in units to sensative to have them fighting each other. might work but not worth the risk. definately would not meet install instructions.

  4. #4
    Join Date
    Feb 2004
    Location
    michigan
    Posts
    677
    They must have their own exhaust and intake. No sharing allowed.
    I am the "Wally". All others are meer imitations of the original.

  5. #5
    You also need to make sure you have the correct clearances.

  6. #6
    Join Date
    Mar 2006
    Posts
    92

    CONDENSATION ON STRUCTURE

    I guess one of the reasons I didn't want it to poke out the side of the house is that I was trying to avoid the cedar siding collecting of the condensation.

    Is there a way that minimizes the condensation blowing back at the house - saw a few little terminations online.

    Also, the furnace is the Infinity MVB080 - Is one size PVC better (or more efficient) than another? Basically the PVC will exit the right side of the furnace with a short nipple and then 45 up and roll into the 45 above (that is pitched) and 90 once at ceiling and head about 10-11' before doing a 45 to get over the foundation and then another 45 above the sill plate before poking out the house.

    Total length of run from the furnace is about 15-16' inside the house and if you count the (4) 45 deg elbows and the (1) 90 I'm at three 90's total.

    So, what size PVC... would you use?

    I have to notch a 2x12 joist (about 2" deep and 8" wide) and maybe knockoff the corner of the concrete (top of the foundation wall) this would be so the two side by side pvc's could offset up and out.

    The above notching would be my responsability as would moving the water pipe in the way, not that big a deal but it makes a difference in what size pvc AS TO HOW DEEP TO NOTCH THE BEAM.

    I Don't like the thought of that but the good thing is that this 2x12 is parallel w/the foundation and runs about 3" away.

    The notch in the 2x12 floor joist is a must if I don't opt to go up and out the roof, I do not want to make another hole in the roof if I can help it.

    Another good thing is the notch is only about 6" away from the steel I-beam in the center of house, also there is an interior finished wall about 6" in the other direction from where the notch would be (for the 2 pvc's exiting) the wall is about 1/8" shy of the 2x12 now, I think I'd shim the interior wall (mechanical rm wall) for support and the other side rests atop the I-Beam) - don't have any room to sister this beam, possibly glue and clamp a relatively short 2x6 directly above this notch.

    They (2-contractors who bid) weren't real specific about pvc size but said I could probably get by w/2" ...

    I can ask for 2", 2 1/2" or 3" just as long as I give them room...

    Thanks


  7. #7
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,743
    whatever install manual specifies is the size you need. bigger is not better unless required, just costs more.

  8. #8
    Join Date
    Aug 2002
    Posts
    1,647
    For a 80k btu infinty 2-stage vs furnace:
    Altitude:0-2000______ 1 1/2 inch 30ft with 1/90, 25ft w 2/90, 20ft w 3/90, 15ft w 4/90, 10ft w 5/90, 5ft with 6/90
    2inch 70ft with up to 6 90's

    2001-3000__________ 1 1/2 inch 26ft with 1/90, 21/2, 16/3,11/4,6/5
    2 inch 70ft up to 6 90's

    3001-4000___________ 1 1/2 inch 25ft with 1/90, 20/2, 15/3, 10/4, 5/5
    2 inch 70ft up to 6 90's
    etc...

    2 inch is the maximum size recommended with that size furnace..

    Note: Assume two 45's equal a 90... Long radius elbows are desirable.. Elbows and pipe sections within the furnace casing and the vent termination should not be included in vent length or elbow count..Size both the combustion air and vent pipe independantly, then use the larger diameter for both pipes.. Do not use pipe size greater than those specified in table or incomplete combustion, flame disturbance, or flame sense lockout may occur.

    You might want to find a contractor that does installation by the book not someone that does not understand how to properly size the vent pipes.. What else does he not know how to do?

    Installation is very important,, the contractor should be specifying the size not you.. This concerns me..

    Goodluck
    J

  9. #9
    Join Date
    Feb 2006
    Posts
    3
    I have had a pvc vent pipe out the side of my rough, unfinished cedar shake house for 15 years. No condensation problems. It is also under an overhang and in the shade for most of the day. You should have no problems.

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