backdrafting smoke at pipe connections

1750 · Nov 9, 2014

Hello, everyone. Our chimney is on the windward side and catches a lot of prevailing wind. When it's really blowing it can push smoke back down the pipe and out the joints in the double-walled pipe. Any suggestions for reducing this? It doesn't happen often, but when the wind is just right, it pushes enough smoke out into the room to be irritating. I was wondering if there was maybe a fire-rated tape, or something I could seal the joints with? Or, any other approaches folks have found to work?

Thanks in advance.

begreen · Nov 9, 2014

You might try a vacu-stack cap. It's designed to mitigate this problem.
http://www.chimneycaps.com/ICP_pages/products1.html

1750 · Nov 9, 2014

begreen said:
You might try a vacu-stack cap. It's designed to mitigate this problem.
http://www.chimneycaps.com/ICP_pages/products1.html

Thanks, begreen.

I'm assuming from the existence of this product that this is a pretty common problem.

DougA · Nov 9, 2014

If you seal the connections, it's likely that the back pressure will simply be worse at the stove. Correcting the problem at the source is the best solution and a cap like this is far cheaper than adding more chimney.

1750 · Nov 10, 2014

Thanks, Doug. Have you used this product?

I can see how it might improve backdraft, but from the design I was worried it might reduce desired draft -- which is a little thin on this chimney as it stands.

Heatsource · Nov 10, 2014

I've sold a bunch of these:
http://www.efireplacestore.com/cpf-14908.html

they seem to work ok, a bit of a pain to clean but better than smoke in the home

begreen · Nov 10, 2014

1750 said:
I can see how it might improve backdraft, but from the design I was worried it might reduce desired draft -- which is a little thin on this chimney as it stands.

If the draft is already marginal, I would add a 3' length of pipe when up there replacing the cap. Brace if necessary.

1750 · Nov 10, 2014

Heatsource said:
I've sold a bunch of these:
http://www.efireplacestore.com/cpf-14908.html

they seem to work ok, a bit of a pain to clean but better than smoke in the home

Thanks, Heatsource. Do you know what's involved in cleaning them? My whole intention with the telescoping section was to be able to clean it from the inside!

1750 · Nov 10, 2014

begreen said:
If the draft is already marginal, I would add a 3' length of pipe when up there replacing the cap. Brace if necessary.

Is there a rule of thumb for when you need to brace?

Since the wind is so unidirectional (it's always blowing in off of the lake), I wonder if I could just a screw a piece of galvanized flashing to the windward side? That wind-blocking cap looks like kind of a soot trap, and my whole goal is to be able to enjoy the stove and stay off the roof!

Thanks again.

BrotherBart · Nov 10, 2014

Every five feet above the roof.

1750 · Nov 10, 2014

Thanks, BB. I don't think even with another 3 ft section we would be five feet above the roof.

begreen · Nov 10, 2014

You could try just adding pipe and see if that improved draft to the point of no smoke leakage. Otherwise, get a better cap.

Heatsource · Nov 11, 2014

1750 said:
Thanks, Heatsource. Do you know what's involved in cleaning them? My whole intention with the telescoping section was to be able to clean it from the inside!

cant clean them from inside.
remove cap, and scrub with a bottle brush...

begreen · Nov 11, 2014

Jags just posted a link to his cap which also has good wind baffling
http://www.menards.com/main/heating...nt-6-s-s-deluxe-rain-cap/p-1323294-c-6894.htm

1750 · Nov 11, 2014

That looks great, and so inexpensive it's certainly worth a try.

Thanks!

Fsappo · Nov 11, 2014

On Long Island, with houses on the water, I used these primarily
http://www.chimneyproductsdirect.co.uk/index.php?page=product&pid=6&cat=1&range=17
I had better success with these when compared to the vacu stack styles. Almost everyone reported a steadier draft with the smoke issues resolved

begreen · Nov 11, 2014

Interesting idea. Do you order direct from Ireland? In a salt water environment have you noted any corrosion issues between the stainless and the aluminum?

Fsappo · Nov 11, 2014

Nope, someone..I think Village Wholesale...trying to remember, stocked them. I don't think is was BAC. It was called the "Aerocowl and looked similar to that photo. Im gonna check my Distributor books now. It brings back memories.

Fsappo · Nov 11, 2014

I'm drawing a blank. I don't recall them being an import. Maybe Z-flex or magnaflex made them? Worked great though. Also helped a ton with wind induced overdraft

begreen · Nov 11, 2014

I think you are correct, it was sold by unova, but the old links no longer work. I tried Zflex's website but didn't find it listed there.

bag of hammers · Nov 11, 2014

1750 said:
Thanks, BB. I don't think even with another 3 ft section we would be five feet above the roof.

Agree with begreen - more pipe is step 1. If you're barely 2' now you're possibly not code compliant (?) My 2 c... get 3' section, might cure the draft issue. And add a brace (while you're up there) regardless. Rock solid. Wind can howl, snow / ice can pile up, it won't budge. You can stick on yet another section if need be if the brace is already there. My stack was just under 5' - brace not required - but I added it anyway, after seeing what extreme winter can do out here to a chimney (neighbor's). $40 or so, 30 minutes of my time, peace of mind.

1750 · Nov 11, 2014

Does anyone have a link describing installation of a brace? I might have to pay someone to do it, as that 10/12 pitch admittedly frightens me a bit, but it depends on what I have to get done once I'm up there.

Thanks, everyone.

UPswede · Nov 11, 2014

I think Northline express has an instructional video for bracing on their website.

begreen · Nov 11, 2014

This is from DuraVent's installation manual:

If the chimney extends more than 5 feet above the roofline, an Extended Roof Bracket must be installed at every 5-foot increment of chimney height above the roofline, leaving no more than 5 feet of chimney extending above the last pipe bracket. The Extended Roof Bracket consists of the Pipe Band, the Adjustable Legs, and the Roof Brackets.

1. Mount Pipe Band: Slip the Pipe Band around the chimney and secure by tightening the nut and bolt.

2. Attach the Legs: The Adjustable Legs of the assembly will adjust from 67" to 114". Secure one end of each Leg to the Pipe Band using the nuts an bolts included (2 per Leg).

Position the Adjustable legs so they form approximately a 60° angle with the chimney, and with each other (Figures 16 and 17). Be sure that there is at least 3" of overlap between the top and bottom halves of the Adjustable Leg.

In order to secure Legs in proper position, there is a hole provided in the outer leg where the outer and inner halves overlap. Use a 1/4" drill bit to drill through the inner leg at that location. Use the nut & bolt provided to pin the Adjustable Legs in position.

3. Install Roof Brackets: Mount the two Roof Brackets where each of the Adjustable Legs meets the roof, using (6) 1" roofing nails per bracket. Seal the nail heads carefully with a non-hardening, waterproof sealant. Attach the bottom end of the Adjustable Legs to the Roof Brackets using the nuts & bolt provided

Screen Shot 2014-11-11 at 7.16.29 PM.png

1750 · Nov 11, 2014

Thanks, begreen. That doesn't seem too complicated. I'm surprised you just nail through the shingles into the decking -- I've always worked diligently to not poke holes in my roof!

Thanks again.

backdrafting smoke at pipe connections

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