Warm Wall

[Joe Pelonio]

This morning I was standing in the hall just outside the shop door (room over garage) talking to my wife. I happened to lean on the wall long enough to notice it was really warm. On the other side of it is my daughter's closet, so I popped her door open long enough to confirm no fire or smoke or anything.

Thinking it through, and poking around in the garage, I have verified that the
vent stack for the gas furnace and water heater goes through there. When she wakes up later I'll check to see if the closet wall is also warm. It's 27 here so the furnace is going pretty steadily, but it seems to me that the inside of the wall should not be warm, with triple wall duct, unless there's a leak.

Anyone have any thoughts on this before I cut into the wall tomorrow?

[Mitchell Andrus]

There's probably zero air change in this space, so I'd expect it t get toasty in there. Drill a small hole and insert a tube. Draw some air out and test with a hardware store-bought CO2 testing kit.

[Joe Pelonio]

There's probably zero air change in this space, so I'd expect it t get toasty in there. Drill a small hole and insert a tube. Draw some air out and test with a hardware store-bought CO2 testing kit.
Good suggestion, a small hole is a lot easier to repair than a pair of 6' seams.

I'm also going to have a look from the attic crawl space, the opening is just a few feet from there.

[jeremy levine]

I think the check you want is carbon Monoxide not CO2 which is heavier then air.

[Mitchell Andrus]

Correct, monoxide. CO2 is soda fizz - like what's goin on inside my brain. Nyquill is wonderful stuff if you don't have to drive or think.

Barkeep, I'll have another, make it a double.

[Chris Padilla]

As you said, Joe, exhaust non-destructive investigation to minimize your work as much a possible. That is this engineer's (i.e. lazyman's) creed! :D

[Joe Pelonio]

My wife had a good suggestion. Drill a 1" hole and stick a canary in there.

Wish me luck, I'm climbing up in the attic now. I figure if the outside wall of the pipe is hot there it would be in the wall too.

[Joe Pelonio]

Check me on this. I have determined it to be a non-issue, subject to verification by any experts. I cranked up the furnace and waited a while to climb up.

First, I have more than my share of abandoned mud dauber nests up there, otherwise all is clean and dry so that's good.

The vent does go up through that wall, then it takes a 45 and goes up and toward the west, another elbow and up through the roof. When I touch the outside of the pipe I have to remove my hand quickly because it's hot. It makes sense that it would be even hotter closer to the source, in the wall, so would make the wall feel warm.

I also noticed that the blown in insulation was right up against it, and it too was hot. While there, I decided to remove it from that area, leaving about 6" of space around the pipe, and the sheet metal square around the pipe free of insulation.

[Jim Becker]

I also noticed that the blown in insulation was right up against it, and it too was hot. While there, I decided to remove it from that area, leaving about 6" of space around the pipe, and the sheet metal square around the pipe free of insulation.

Yes, the insulation should not be touching the hot vent pipe.

[Chris Padilla]

I wonder if you can wrap it with something to help insulate it better from the surroundings? I wrapped my newly installed/fixed/repaired duct with Reflectex (foil on both sides of bubble wrap, basically) but I believe they say it is ony good to 180 F and I bet your vent is hotter than that.

One question begs from this: why are you sending all that nice heat outside?! :) Is there anyway to recapture it...use it?

[Matt Meiser]

One question begs from this: why are you sending all that nice heat outside?! :) Is there anyway to recapture it...use it?

High efficiency furnace and hot water heater would do it. They use regular PVC pipe for venting.

[Joe Pelonio]

I wonder if you can wrap it with something to help insulate it better from the surroundings? I wrapped my newly installed/fixed/repaired duct with Reflectex (foil on both sides of bubble wrap, basically) but I believe they say it is ony good to 180 F and I bet your vent is hotter than that.

One question begs from this: why are you sending all that nice heat outside?! :) Is there anyway to recapture it...use it?
I'd rather not tear up the wall, but it seems like a vent in it would allow all that warm air to escape into the house and help warm it.

And Matt, this is still the original furnace age about 25, the water heater newer but yes, new efficient ones would help. We're planning to sell and move within 2-3 years so I'm not sure we'll change them soon.

[Al Willits]

Can you tell if this is single or double wall vent?
Class B or double wall usually twists together and single wall gets screwed together, usually..

Anyway code in this part of the world is 1" clearance for double wall and 6" clearance to combustibles with single wall.

Usually when vent is run though a wall its class B and oval shaped.fwiw

Single wall can get hot enough to blister the skin, 300-400 degree's is not uncommon, depending on how far from the source.
Double wall will get hot but no where near single wall, still prob hot enough to burn the skin.

You can't drop the stack temps very much with out loseing draft.
No draft, people die.

Hope this helps a little

Al

[Joe Pelonio]

Al, It's at least double from just under the garage drywall the rest of the way out, 8" round. I was able to touch it but not for long, and didn't get burned and it's twisted together. I think it's round thru the wall too, because that closet wall sticks into the closet 4" further than the rest of that room's wall.

The warm wall is not a problem just that I hadn't noticed it before, but then we didn't spend much time at that hallway spot while the furnace was going for a long time until today. I am thinking that cutting a vent into the drywall in the hall there would allow that nice warm air to help heat the upstairs instead
of being wasted.

[Al Willits]

Doesn't sound from what you say that its getting to hot, not sure how much heat you'd recover, but that the hay, give it a try and see what happens, just remember if the vent rusts out, it might be easier for flue products to enter the house..

Al

[Rick Hutcheson]

When it is hot the heat will come out.
But then think about the rest of the time. There should be clearance around the pipe that goes all the way to the attic. You have created an open flue space to draw heat out of the area right up to the attic when the pipe is not hot. Now to guess if the pipe is hot more of the time than it is cold.

[Joe Pelonio]

What I need, if such a thing is available, is a vent tat opens at 75 degrees or so, then closes when it cools. I'll have to look into it.