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96% Efficient Furnace on Second Floor

mrcline Member Posts: 3
I will be replacing my 17 year old furnace/AC with a 96% efficient one but my furnace is located in a utility room on the second floor. My concern is with how the installers are suggesting the venting be ran horizontally through the wall.

I was doing some research and the vapors coming out are corrosive to vinyl siding. The existing furnace is still using the exhaust pipe straight up through the ceiling/attic and out the roof. That's being replaced with with double-layer(Not sure on the wording) metal pipe for the water heater.

My question... is venting out the side of the house on the second floor correct or even code? Will it eat a way at my siding?


    JUGHNE Member Posts: 10,278
    If there is going to be some roof work anyway, why not run the 2 PVC pipes for the new furnace up thru the roof? This is quite common.
    Assuming the furnace is near the center of the 2nd floor it sounds easier than wall penetrations.
  • mrcline
    mrcline Member Posts: 3
    @JUGHNE - The furnace room is located next to an outer wall. Far side of the house, not in the center.
  • Jamie Hall
    Jamie Hall Member Posts: 20,416
    Corrosive to vinyl? Say what? Vinyl doesn't corrode. Aluminium might, if the pipe isn't pitched properly and condensate can drip on the siding, but not vinyl. However, the heat and combustion products might stain vinyl -- but even that shouldn't be a problem is the pipe is installed correctly.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 10,278
    edited January 2021
    I guess if I was the installer it would be tempting to just punch thru the wall.
    However, I have had issues with the inlet frosting shut under certain conditions, if inlet and outlet are close.
    Easy to clean at grade level....not so on 2nd floor.
    Also if there is a soffit outside, I believe you have to pipe out past that if it does not have correct vertical clearance as per the manual.

    With exhaust a straight pipe thru the roof, looking like another sewer vent, and the inlet spaced farther away than you might have on the wall, may avoid the frosting shut.
    HVACNUT Member Posts: 4,856
    edited January 2021
    Sidewall venting is one hundred percent fine, as long as the installer adheres to the manufacturer's instructions. Which most manufacturers cover in detail. 
    HVACNUT Member Posts: 4,856
    Now let's talk about running those new refrigerant lines. Is the existing A/C R22?
  • mrcline
    mrcline Member Posts: 3
    @young, I was referring to the vented byproduct having a "corrosive" effect on the vinyl siding. Poor choice of words on my part, should have said staining. Ultimately, I guess, I just don't like the idea of having something hanging out the side of my house potentially dripping down the side.

    @HVACNUT - The existing unit still uses R22. The lines run inside the walls. I never asked about that, should I be concerned?

    I do appreciate the info from everyone.
    EBEBRATT-Ed Member Posts: 13,096

    The exhaust shouldn't drip much. The pipe is pitched back toward the furnace
    HVACNUT Member Posts: 4,856
    There are flush kits available, but IMO a new line set is the way to go. Can it be routed up into the attic, across, out, then down?
    Additional line set length over the condensers "factory charge" must be figured in for adding refrigerant. 
    You won't get staining from the exhaust gases themselves. But again, as long as the installer opens (or knows) the book.
    Combustion air is very important. The new furnace will have a connection to bring in outside air for combustion. Use it. 
    The water heater is going to be vented in double wall, B vent? Make sure there is sufficient combustion air for it as well.
  • GW
    GW Member Posts: 4,592
    Side wall- cake. 

    Never seen staining
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]