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Thread: Furnace venting

  1. #1
    Join Date
    Apr 2019
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    Furnace venting

    Hi,
    I am having trouble routing the intake/exhaust for a furnace and combi boiler that are both direct vent, basically where to have them exit the house. The house is two stories with a walkout basement with a deck across the back that wraps around to a walk way down the side closest to where the utility room is located.

    I think I have 4 options but none of them are great.
    1) Vent to the side closest to the furnace. This is either over the deck walk or too close to the side door/window. I might be able to make one work but I won't be able to vent both appliances to that location. Venting either of them will require relocating the dryer vent

    2) Run to the opposite side of the house. This will be close to 40' of run and will require me to start the vent below the beam to get the required pitch. I will need to run 3" pipe for the boiler

    3) Vent up through the roof. There is a shared 2x4 wall that stacks all the way up to the attic. Downside is the roof is 10/12 and the wall is ~20 from the back. Doable but I'd have to hire a Sherpa

    4) Run to the back wall elbow down and put the vent 18” or so above grade. If I go straight out the back the vent will be over the deck and too close to the windows. There is a chimney chase, if I run to the back of the chase and come at the bottom I'll be far enough from the windows. Downside to this approach is that I’ll be required to run a condensate pump at the bottom where the vent drops down from the ceiling to the ground level. I like to just pitch this last 2’ section down so it drains outside, apparently this is not allowed.

    On a related note, the furnace manual has modified requirements for spacing between the exhaust and intake of other appliances when installed with another furnace. Do those same rules apply to the boiler?

    Hoping somebody might have seen something like this before and have a better idea.

    Thanks
    Jake

  2. #2
    Join Date
    Dec 2007
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    Quote Originally Posted by Call_me_Jake View Post
    Hi,
    I am having trouble routing the intake/exhaust for a furnace and combi boiler that are both direct vent, basically where to have them exit the house. The house is two stories with a walkout basement with a deck across the back that wraps around to a walk way down the side closest to where the utility room is located.

    I think I have 4 options but none of them are great.
    1) Vent to the side closest to the furnace. This is either over the deck walk or too close to the side door/window. I might be able to make one work but I won't be able to vent both appliances to that location. Venting either of them will require relocating the dryer vent

    2) Run to the opposite side of the house. This will be close to 40' of run and will require me to start the vent below the beam to get the required pitch. I will need to run 3" pipe for the boiler

    3) Vent up through the roof. There is a shared 2x4 wall that stacks all the way up to the attic. Downside is the roof is 10/12 and the wall is ~20 from the back. Doable but I'd have to hire a Sherpa

    4) Run to the back wall elbow down and put the vent 18” or so above grade. If I go straight out the back the vent will be over the deck and too close to the windows. There is a chimney chase, if I run to the back of the chase and come at the bottom I'll be far enough from the windows. Downside to this approach is that I’ll be required to run a condensate pump at the bottom where the vent drops down from the ceiling to the ground level. I like to just pitch this last 2’ section down so it drains outside, apparently this is not allowed.

    On a related note, the furnace manual has modified requirements for spacing between the exhaust and intake of other appliances when installed with another furnace. Do those same rules apply to the boiler?

    Hoping somebody might have seen something like this before and have a better idea.

    Thanks
    Jake
    What's your installer say?
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  3. #3
    Join Date
    Apr 2019
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    Thread Starter
    Thanks for the reply.
    The installer wants to do what's easiest for him. Says we should drop the intake, let the furnace draw combustion air from the basement and run the exhaust to the far side of the house. Boiler can run to the near side and I can figure out something else for the dryer duct as he's not installing that.

    I am not huge fan of this idea for a few of reasons, one of them being it will drop the pipe below the beam and I spent a lot of time with the designer keeping the ductwork above the beam. Another is I'll most likely need a booster to re-route the dryer duct

    As for the spacing between the two appliances if they came out near each other, he's telling me they need to be 10' apart. I am having a hard time with this because the manual says 12" to other combustion air inlets, and as little as 3" between intakes when installing two furnaces.

  4. #4
    Join Date
    Jul 2007
    Location
    Virginia
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    Quote Originally Posted by Call_me_Jake View Post
    Says we should drop the intake, let the furnace draw combustion air from the basement and run the exhaust to the far side of the house.
    Is the basement area where the furnace is located, large enough to provide proper combustion air?

    Does the manufacturer allow this venting option in their installation manual?

    Do you have the model numbers of the furnace and boiler?

  5. #5
    Join Date
    Jun 2012
    Location
    Northern NV
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    My opinion is to run to the roof and use a concentric termination for both the furnace and boiler as with a concentric you can locate as close as 8" O.C. if ok with the mfg's instructions for multiple vents.

    If you are over a deck or patio and in a cold climate you WILL have ice.

  6. #6
    Join Date
    Apr 2019
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    Thread Starter
    Thanks guys for the input

    I will get the model numbers but this is an option in the furnace manual and the basement is unfinished I assume there is enough volume. The boiler needs to be vented to the exterior.

    Going up through the roof would be the cleanest but probably the most work.

    Appreciate any other ideas/opinions.

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