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Alternative options for furnace intake and exhaust pipes

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Calj

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I am looking to replace my deck and need help with redesigning my furnace intake and exhaust pipes. The furnace intake and exhaust pipes with the current design going through the edge of the deck beams are a bit of an eyesore and I have concerns about the structural integrity of the deck framing with this design if I put in a new deck. I understand the reasoning behind the current furnace pipe setup for obtaining clean air and moisture output, but I cannot envision other options. What alternative design options do you recommend with the intake and exhaust pipes? See attached current setup.
 

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FishScreener

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The setup could use a stiffener, on the bottom, you should be able to find something suitable from Simpson Strong-Tie. But other than that, it is structurally sound, and I’m more concerned about the spacing on the supports for the railing being too far apart.
 

fixitron

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There are 2 problems with your current installation. There is NO slope to the exhaust pipe and I question the insulation. You can run a vent pipe that far outside if it is in an insulated box, so I don't know if what appears to be ducting insulation would qualify. Insulation does not stop the flow of heat (which is always from higher to lower temperature). It only slows it down. In the winter, the pipes will be cold when the boiler has not run in a while. As soon as the boiler starts up, the flue gases will condense a lot of moisture. It will take at least several minutes for the piping to warm up. That water will sit in the level piping and can freeze when cold enough outside. That flue gas is a bit above 9% water vapor.
 

Calj

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Thanks for the feedback. There is a very slight upward slope with the pipes across the span (difficult to see). The current setup spans 8' outside the house and the pipes are 3". I have used the current setup for at least 10+ years without issue (when I bought the house). Based on what I have read from you and others, I think I must keep the current setup. I will ensure we use a stiffener with the setup. The boxed insulation recommendation is interesting; do you have any pictures of what this might look like?
 

breplum

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You must have a big furnace. I cannot recall a furnace ever needing larger than 2" unless a long run dictated that spec.
You do not need that plate termination if you used spacing in adjacent joist bays. Also!: The intake can often come from a downward facing elbow just outside the dwelling (or if crawlspace is well ventilated, from the crawlspace only )
Typically the intake and exhaust do not need to match.
The furnace comes with a specification chart for vents that dictate all the variable options.
If it is a Bryant/Carrier furnace I might have a venting sheet if you don't.
 

Calj

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It is a Goodman furnace and it looks like they expanded the piping from 2” to 3” which the manual says is ok to do. I think the intake vent was extended to outside the deck because the central a/c is also in the same area outside and shares the furnace fan. I did look at the manual today and did not see much in terms of creative options. Everything looks like it is in compliance as is. Attached are more pictures of the furnace setup and manual.
 

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breplum

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The quantity of elbows is likely why it is 3".
I have often installed similar but with the intake just stubbed to the outside.
It has nothing to do with the outdoor condenser at all.
I am not going to take this further except repeat that:
Typically the intake and exhaust do not need to match.
The furnace comes with a specification chart for vents that dictate all the variable options.
 

Calj

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I tried calling Goodman. Unfortunately, they will not provide technical advice to homeowners.
 

fixitron

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Every one of these scenarios has the piping terminating just outside of the exterior wall, not 8 ft. away from the wall.
The slope on that 8 ft. is not 1/4"/ft., which would be a 2' drop over 8 ft.. The flue pipe should slope back toward the furnace, but if you transition from 2" to 3" on a horizontal run, you will be trapping water in the 3" pipe.
Is there another wall that it could be vented out that does not have a deck or other impediment?
 

Calj

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Thanks for your insights. Unfortunately there is not another wall to exit. The furnace is placed in the center on the backside of the house with a window right next to it, and the deck spans the full width on the backside of the house.

The water heater is in the same area and is connected to a roof vent, but I know the furnace and water heater vents cannot be connected.
 
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