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Our gas furnace intake (one of them, there are other intakes inside the house) currently comes out the side of the house but under a brick patio. It seems that the previous owner of the house extended that intake by added pipe underneath the brick patio, and enclosed in plywood from all 4 sides.

It seems that the pipe that was added did not fit properly in the pipe coming out of the wall. (Both appear to be 6" wide male end). Also there is some sagging of the brick patio, probably because part of it has the original concrete steps underneath it, and the rest doesn't.

What is the proper way to do this? Will I be able to find the right size of pipe that will fit with what's coming out of the wall?

Here the intake coming out of the wall under the patio:

Coming out of the wall

Here's the run with the brick removed:

Under patio with brick removed

And, here's the final vent:

enter image description here

Please see this photo album for the rest: https://imgur.com/a/0pd42xK

  • Hello, and welcome to Home Improvement. Where are you located? And, I'm no pro, but I'd be concerned about fumes endangering whomever was on the patio. – Daniel Griscom Apr 13 at 19:00
  • Thanks. I'm in Alberta, Canada. I've just discovered that this is an intake, not an exhaust like I thought it was. I've updated the question. – user453441 Apr 13 at 19:16
  • If you don't want the patio to sag, be sure to use lots of compacted gravel, packed in layers, pack sand into the gravel, and use only a thin layer of sand over the gravel, enough to level the last bit of unevenness out. – K H Apr 14 at 2:27
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I do not think extending it under the patio is "the right way" to do it.

If rerouting it from the source up through the house is not an option then -

I would put a 90∘ elbow on it and run it up the exterior wall a bit. Build a chase around it (box it in to keep it from getting crushed or damaged), similar to the one under patio.

The elbows have male and female ends, the male end should go into the existing pipe, but you will not be able to get screws in it so adhesive will have to do. Add another elbow and a screen.

Put a tilted cap on the new chase long enough for rainwater to drain off without getting sucked into the intake (similar to the the one in your photo of the final vent.) You could build a little removable wall shelve/table over it for your patio living space.

Putting it under the patio seems like an expensive way to ensure more expense and problems down the road.

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