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Old 01-31-2017, 10:57 PM   #31
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Your stovepipe is far too short for the "chimney effect" to work.

https://en.wikipedia.org/wiki/Stack_effect

Most stove manufacturers require 12' of 6" pipe from the collar on the top of the stove to the top of the chimney. I'm not a stickler for "code" or anything but if you use that as a rough guide, you can see you're way too short.

That flexible corrugated stuff isn't aluminum is it? If so, you need to change that too. Aluminum can not handle the high temperature wood smoke.
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Old 01-31-2017, 11:21 PM   #32
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Originally Posted by jazty View Post
I have a decent time invested in chimney installation and research, so I'll throw my 5 cents into the ring (Canada no longer has pennies, you see).

Most chimney draft issues are due to bends, an outdoor installation, or not enough chimney height. Of all of these issues an outdoor installation is the scariest. With the chimney completely outside it's possible for it to cool enough to overpower a lightly burning fire, which can dump huge amounts of carbon monoxide into the living space.

I don't expect you'll ever get a good draft with such a short stack employing a 90 elbow. Elbows considerable reduce draft no matter the chimney they're installed on. They also encourage creosote build up.

Second, a horizontal termination is inevitably going to cause back draft when the wind is right (wrong?). Heck, on a windy day it could potentially over power even a chimney draft blower. The problem has to do with wind direction and pressure.

When the wind is blowing towards the chimney cap side of the bus it will create a high pressure zone that will easily over power the chimney's draft and thus send air down the chimney. There is no natural draft chimney cap that can prevent this. They are meant to be installed vertically and above the roof line.

Contrariwise, when the wind is blowing towards the side of the bus without the chimney cap you will get a negative pressure on the chimney side which will suck the air out the chimney.

When the wind is blowing from the front or back of the bus you'll have neutral pressure on the sides.

Here's a sweet picture some kindergartener drew up for me (jk.. I drew it. how embarrassing):


The only solution that will work 98% of the time is a vertically mounted chimney cap that is above the roof line. I say 98% of the time because the wind can come down at you vertically if you're parked next to a structure with just the right shape.

While not ideal, a short term solution would be to add another elbow and bring the chimney termination above the roof line. You are likely to still get smoke rolling out the door when loading, but at least it shouldn't backdraft into the living space when the door is closed.

Also, it seems that single stage wood stoves require less chimney draft to operate than wood stoves that are built with a secondary burner. Secondary burners usually have a couple internal 90 corners for the smoke to travel while it gets re-burned. They result in a cleaner burn and more heat per weight of wood, but require a good chimney installation. Do you know which kind you have?

I know a lot of this has already been said by previous posters, but puking up a complete idea seemed easier than replying to a handful of quotes

Good luck!
Thank you for this info, i had not considered the cooling effect of the outside chimney.
hmmm maybe time to get out the sawzall. lol
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Old 01-31-2017, 11:29 PM   #33
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Quote:
Originally Posted by jazty View Post
I have a decent time invested in chimney installation and research, so I'll throw my 5 cents into the ring (Canada no longer has pennies, you see).

Most chimney draft issues are due to bends, an outdoor installation, or not enough chimney height. Of all of these issues an outdoor installation is the scariest. With the chimney completely outside it's possible for it to cool enough to overpower a lightly burning fire, which can dump huge amounts of carbon monoxide into the living space.

I don't expect you'll ever get a good draft with such a short stack employing a 90 elbow. Elbows considerable reduce draft no matter the chimney they're installed on. They also encourage creosote build up.

Second, a horizontal termination is inevitably going to cause back draft when the wind is right (wrong?). Heck, on a windy day it could potentially over power even a chimney draft blower. The problem has to do with wind direction and pressure.

When the wind is blowing towards the chimney cap side of the bus it will create a high pressure zone that will easily over power the chimney's draft and thus send air down the chimney. There is no natural draft chimney cap that can prevent this. They are meant to be installed vertically and above the roof line.

Contrariwise, when the wind is blowing towards the side of the bus without the chimney cap you will get a negative pressure on the chimney side which will suck the air out the chimney.

When the wind is blowing from the front or back of the bus you'll have neutral pressure on the sides.

Here's a sweet picture some kindergartener drew up for me (jk.. I drew it. how embarrassing):


The only solution that will work 98% of the time is a vertically mounted chimney cap that is above the roof line. I say 98% of the time because the wind can come down at you vertically if you're parked next to a structure with just the right shape.

While not ideal, a short term solution would be to add another elbow and bring the chimney termination above the roof line. You are likely to still get smoke rolling out the door when loading, but at least it shouldn't backdraft into the living space when the door is closed.

Also, it seems that single stage wood stoves require less chimney draft to operate than wood stoves that are built with a secondary burner. Secondary burners usually have a couple internal 90 corners for the smoke to travel while it gets re-burned. They result in a cleaner burn and more heat per weight of wood, but require a good chimney installation. Do you know which kind you have?

I know a lot of this has already been said by previous posters, but puking up a complete idea seemed easier than replying to a handful of quotes

Good luck!
That's pretty much what I was saying, right?
I've burnt enough bbq wood to know that if you're seeing smoke, you're not burning efficiently enough. The smoke is in the cooking chamber, but once it's drafted out the stack and mixed with enough air... You'll barely see smoke.

I know it's apples & oranges, but I feel the principles are the same.
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Old 02-01-2017, 09:03 AM   #34
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Quote:
Originally Posted by Carytowncat View Post
Thank you for this info, i had not considered the cooling effect of the outside chimney.
hmmm maybe time to get out the sawzall. lol
When I mentioned outdoor chimneys I was think of these two styles installed on tall houses:


You want to keep as much of the chimney inside as possible and exit through the roof. You get two benefits out of it. It'll add a bit more heat to the living space and the heat in the living space will keep the stack from cooling down too a dangerously low temperature. With the little stacks that school buses are likely to have installed you won't see drastic chimney cooling of the outdoor portion. I mentioned it previously to complete the thought, but its mostly an issue for houses where the home owner is looking for short cuts...
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Old 02-01-2017, 10:46 AM   #35
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the aluminum should handle the temperature of a "NORMAL" fire.. but when the draw is slow the stack temperature rises... and *IF* god forbid you should have a chimney fire or even a small amount of creosote burn off it WILL MELT!..

the other issue with flexible pipe is that the ridges in it
1. slow down and create turbulence in the exhaust-flow. whuch makes the draw to outside harder for it to maintain.

2. the inside ridges are a Magnet for creosote to stick and form and is also very tough to clean effectively... see above about a chimney fire..

-Christopher
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