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Old 01-29-2017, 04:46 PM   #1
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chimney blow back help

i have had a wood stove for a few months now. every once in awhile i get high winds that create blowback. can anyone help me?

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Old 01-29-2017, 04:55 PM   #2
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How are you set up outside? )
Haven't messed with chimneys in years, (But I've modified BBQ smokers) but you've got to fine tune the draft to get a clean efficient burn... And to get that draft, you've got to have length. Most everything I've seen or heard about requires at least 3' above the highest point of roof.

A quick google image search for chimney backflow preventers resulted in some pretty good designs.

Other than that, I got nothin'
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Old 01-29-2017, 05:18 PM   #3
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Old 01-29-2017, 05:20 PM   #4
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its a temporary setup, as its winter and cutting hole in my skoolie may cause issues i cannot repair in 1 days time.
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Old 01-29-2017, 06:35 PM   #5
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I've seen some people that do a 90 on the out side. So the exhaust would be pointing up and not sideways.
Just an observation. I imagine, if there is wind, it is easier for it to travel sideways than downwards.
Noob here, fyi.

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Old 01-29-2017, 06:52 PM   #6
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That set up will not draft properly.... The heated air needs to clear the top of the stack.
I understand what you mean about not cutting into the roof yet, and I'm pretty sure a 90 bend upward and a 3' section of pipe, then the cap will help immensely.

If you're noticing air coming in a blowing your ashes when you open the door... You can guarantee that air is blowing in while the door is closed... Thereby pressurizing the firebox!
Not a good thing!
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Old 01-29-2017, 06:55 PM   #7
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I would suggest a 90 degree fitting just outside the window (or a T, and close off the bottom). Run the chimney up and above the bus by a bit.

Um... is that for-reals chimney tube above the triple-wall? If it's dryer vent tubing I foresee trouble. You might try a couple of 45 degree elbows: one above the stove, run the straight connecting pipe out your collar, then another 45 to take it to vertical.
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Old 01-29-2017, 07:41 PM   #8
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Originally Posted by Dapplecreek View Post
I would suggest a 90 degree fitting just outside the window (or a T, and close off the bottom). Run the chimney up and above the bus by a bit.

Um... is that for-reals chimney tube above the triple-wall? If it's dryer vent tubing I foresee trouble. You might try a couple of 45 degree elbows: one above the stove, run the straight connecting pipe out your collar, then another 45 to take it to vertical.
i thought the same thing about the exterior 90 or at least 45. i was told to try venting straight out. i dont think the weight be supported for an extra 3 feet. or more than a 12 inches.

nope, that is the fake stuff as the 90 will not fit. it is to tall by a few inches. this is temporarily in until my skoolies interior is completed and im certain where i want to place the wood stove. i cant cut during the winter.
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Old 01-29-2017, 07:45 PM   #9
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That set up will not draft properly.... The heated air needs to clear the top of the stack.
I understand what you mean about not cutting into the roof yet, and I'm pretty sure a 90 bend upward and a 3' section of pipe, then the cap will help immensely.

If you're noticing air coming in a blowing your ashes when you open the door... You can guarantee that air is blowing in while the door is closed... Thereby pressurizing the firebox!
Not a good thing!
crap, i doubt the collar can support that much weight though. how much would a 45 and cap help do you think?

no, it isnt blowing my ashed when i open the door or hadnt noticed if it had. however with this new setup i did notice that the area was extremely cold compared to the rest of the skoolie. is that an indication of pressurizing the box?
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Old 01-29-2017, 07:53 PM   #10
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not sure how much advice i can give you here since mine is straight up. I've got 5 feet of piping above my stove and my draft works perfect.
You should have a dampener in the pipe if there isnt on on top of the stove, that will stop some drafts as well as control the amount of air the fire gets. When i open the chute on the front of my woodstove i can actually hear the fire roar up, as well as when i turn the dampener to open more, so with both of those i control my fire pretty damn good.

I hardly know anything about this stuff, and cant tell what type of cap you have but there are different types of caps for different types of fuel stoves such as propane, pellet, wood. Use the correct type of cap for the correct flow for the fuel you use if you haven't already.

my best guess is the combination of short length and going straight out and stopping rather than out than up with an elbow.
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Old 01-29-2017, 08:09 PM   #11
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That set up looks dangerous. I hope you correct it. This may help, A non-commercial service in support of responsible home heating with wood - Installation Rules For Flue Pipes
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Old 01-29-2017, 08:54 PM   #12
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For the support, consider using a 'T' fitting just outside the window. Run it so the smoke comes in the base of the T and then up one side. For the side pointing down, put a cap on it, and support the pipe and the bottom cap with "L" brackets off the side of the bus. Below, parts #21-23 would have an "L" bracket on 'em, or a length of pipe down to where you COULD put an L bracket in. You might also be able to do a hanging support like part #30, hooked over the top of the open window.
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Old 01-29-2017, 08:57 PM   #13
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I agree... The flex ductwork is sketchy at best and I wouldn't dare sleep with a fire burning.
You're dealing with a lot of heat concentrated in that bend.
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Old 01-29-2017, 10:07 PM   #14
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Friend when that flex burns through it will vent into the bus and be a disaster.
I know because i also used dryer vent flex lol
AND i vented in a direction too, and it worked perfectly...until it didnt and blew and filled the bus with smoke is seconds. So i added a 90 and went straight up.


However... a temp solution is to place a sheet of metal in front of the vent, think a flat bridge of sheet metal that blocks wind from any direction besides up or down, which the wind rarely blows from up or down.

Good luck!
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Old 01-29-2017, 10:35 PM   #15
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Friend when that flex burns through it will vent into the bus and be a disaster.
I know because i also used dryer vent flex lol
AND i vented in a direction too, and it worked perfectly...until it didnt and blew and filled the bus with smoke is seconds. So i added a 90 and went straight up.


However... a temp solution is to place a sheet of metal in front of the vent, think a flat bridge of sheet metal that blocks wind from any direction besides up or down, which the wind rarely blows from up or down.

Good luck!
yeah it is sketchy but it worked well when i did a 6in covered by a 7in flex. then the cresote weighted down the old top. i bought a 90...it won't fit. but i like the sheet metal idea for temp. the final plan is straight up and out...no angles.
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Old 01-30-2017, 12:03 AM   #16
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Also my chimney goes right out the window like yours. I couldnt bring myself to cut a hole in the bus roof, especially before i have tested the wood stove for at least a year and KNOW im not going to move it

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Old 01-30-2017, 04:23 AM   #17
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Op- was it you that asked about this a week or two ago?
There was a thread about this. I found it a bit funny that no one but me was saying to run the chimney straight up.
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Old 01-30-2017, 06:41 AM   #18
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good luck with the chimney. There's not enough vertical rise to start a draft. while you use your temporary chimney, maybe something like this will help.

https://www.northlineexpress.com/tje...ad-1-8803.html


good luck
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Old 01-30-2017, 07:51 AM   #19
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thats why I suggest a power vent... they are great for short run or hotizontal chimneys... it creates an artificial draft.. the good ones are variable speed sp they dont create too much of a draft and burn up all your wood.

you can also use a slight draft inducer if you have a sealed stove. a slight positive pressure into the air intake of a stove can induce a draft.. that air amount can be varied for the amount of burn you want. you need a sealed stove for that concept to work, but you also wont get any backdrafting as you air intake is sealed except for the inducer inlet.
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Old 01-30-2017, 08:23 AM   #20
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i have a power vented stove and two propane heaters out in my greenhouse. super easy to vent. i dont think i'd buy another natural draft firebox. all three heaters just have horizontal chimneys straight out the wall. pretty easy. and one of the heaters out in my greenhouse sounds like a trumpet when it starts. always nice to hear that its warm out there.
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