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(OT) Why backdraft on a stovepipe? physics of?how to elimnate it?

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9N'er

01-14-2003 03:50:08

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Well, I should know the answer to this but my mind is not functioning this morning which is fairly typical anyhow.

Why does our small plate steel woodstove have a tremendous backdraft and smoke just billows out into the room until sufficient heat builds up for the stove and pipe to vent correctly?

This year has to be the worst for smoking us out of the camp until the air clears and the stove vents correctly. We might as well just crumple up newspaper wads and set them on the kitchen table and start the fire there...it's that bad.

The only thing I can fiugre withoput studying the subject is the heavier and colder air outside just rushes down the pipestack and that the pressure of that is greater than the pressure inside the stove. Until the heat creates enough pressure we're doomed for black faces, smelly hair and stinky clothes.

What can I do to eliminate this problem?

Well, it's time to shower and wash the stink out of my hair.

9N'er

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Paul

11-25-2003 13:56:55

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Re: (OT) Why backdraft on a stovepipe? physics of? in reply to 9N'er, 01-14-2003 03:50:08

I have a similar downdraft problem with my stove. I have a metal selkirk chimney outside the house and what I understand is that since the chimney itself gets cold, the air in the chimney gets cold and sinks. People with chimneys that run up the center of the house do not have this problem since the chimney never gets cold. Cold air is heavier than warm air therefore you get the reverse draft problem. Something we do which is useful is heat the chimney up with a hair dryer until the draft is going up the chimney. Its apparent when this happens by stirring up the ash. If the ash does not come out of the stove, you are ready to light the paper. Hope this helps you out. If you encase your chimney and insulate then it may help the problem.

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kevin

01-15-2003 15:17:31

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Mine would do this from time to time. I would crack the damper a bit and stuff a propane torch up the chimney from inside the stove and let'er go full bore 'til I got hot air pulling up the chimney. It was pretty apparent when the air was going the right direction. With the hot air pulling up, I would then light my kindling without need of a respirator and it burned fine.
I quit generating theories about what was occasionally causing the downdraft.

fwiw
kevin

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tlak

01-14-2003 14:54:24

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

When the barometric pressure is up its hard to start a fire or keep one going. If you look outside when your stove is going and see the smoke dropping around your house the pressures up. One wood stove manufacture site they told of starting a airtight catalytic wood stove and they went through about a 6 hr process of building the fire up in stages, start with kindling stage burn for two hrs and so on. A local hardware store have a wood stove with two fans one for circulation and the other I was told was used for burning saw dust. The air jets in the bottom kept the sawdust from packing down and smoldering. They burn regular wood and say starting it is a breeze. Throw one piece of paper in and set your wood and its like somebody constantly blowing the flame also can burn most green woods with no problem.

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John,PA

01-14-2003 14:13:47

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

9ner"
We used to dump the wood smoke into the attic. There, we hand\g hams,bacon,and other meats. There is a small window inthe gable ends of the old log house. Never burned up the roof, yet! When you go up to git some meat, the ceiling of the roof and the timers are always black. We always let the windows open in the attic. Sometimes tourists call the fire department. They think our house is on fire. But it is not, really. House is almost 250 years old.

I tell 'ya truely.

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Brian-2N

01-14-2003 13:52:35

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Tom,
My .02. Old industrial plants had to have chimney's of a certain height to operate correctly and efficiently. Willy and Jim have hit on the problem-your chimney's probably not tall enough. As we have 3' accumulated snow on the ground, I doubt you'll be rebuilding the chimney soon.
Getting the chimney hot sounds like the best stop gap measure. I would probably also use firestarters instead of paper. The hotter you ignite the wood, the faster it ignites, and the less smoke you have. An old Boy Scout trick I use, is the bottom of egg cartons soaked in parafin. One or two starts a fire right quick. I usually make a truckload before winter starts. I'm too cheap to buy them at the store.

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Dale-PA

01-14-2003 11:12:38

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Don't burn Pine. Try to avoid wet/unseasoned wood. Don't use artificially stained wood (I did this once for kindling, BIG MISTAKE). These all add to creosote buildup. First off check and/or clean your flue/chimney pipes. I avoid using paper to start my kindling as it provides too much smoke and ash that doeesn't burn off. They sell "Fire Starter" bricks that you can break off and they work EXTREMELY well. Light a small chunk (say 2") put it in the stove, and this will get the air circulating up. Leave your door cracked 1" or so and vent, if you have one FULL OPEN. Build your kindling thereafter. Once caught, add your logs, close your door, and adjust vent, if you have one, accordingly. FYI... depending on how much you burn, check into a Soapstone stove. I got one two years ago, and they are second to none. 1 full fire will radiate heat for 1/2 day once the fire subsides. They are pricey though. Good Luck. P.S. Make sure a good Carbon Monoxide detector is in order also, and of course the standard Smoke Detector. Be Safe.

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Fred OH

01-14-2003 10:20:30

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

On the subject of the cresote in the chimney....I asked my sharp minded aunt (I always picked her brain) about this and she said that they always threw a hand full of salt in the stove once a week. Any other comments on using salt? I also heard that something called brimstone was common....whatever that is. L8R....Fred OH

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DON TX

01-14-2003 19:18:40

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Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Fred OH, 01-14-2003 10:20:30

My Yupper friend throws an aluminum can in the fire every so often to clean his. My 8" stovepipe castiron firebox smokes up the shop while my 6" doesn't. No noticeable leaks but seems to come from the front of the box. Same height flue cover on both. Can't figure it out.
DON TX

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dave 50 8n

01-14-2003 09:46:30

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

When we first moved in to our current place, we had a huge earthstove brand woodstove w/an 8" vent. It was necked down to a 6" vent, which included a jog. We'd get big clouds of smoke back inside the house if we opened the door when the fire was going well, so I can sympathize.

Now we have new stove that matches the vent pipe. I suspect you have creosote buildup in your pipes, especially, since you say this is the worst year. Something's plugged up. Has it been cleaned recently? Pine and sappy woods make lots of gunk.

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ButtonRock

01-14-2003 09:27:47

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

I tried for years everything I could think of to eliminate this problem. I finally gave up to the task of putting a vaccuum on blow and forced the air to reverse up the chimney. I did this every morning during the winter for three years. Now I burn in an outdoor wood boiler and the stove sits waiting for an emergency in the basement. Now I light it once a year, fill it twice a day, cut twice as long logs and my mind can worry about health issues instead of burning down the house. Best of luck

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Les, TN

01-14-2003 08:37:25

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Of course, there's always the 'lectric powered draft fan. Stick one 'o them in yer pipe and no more smoke. They work great!

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A Link...

01-14-2003 08:06:30

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Here is a link that explains better than I did...

Salmoneye

Starting A Fire In Stove Or Fireplace

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BC Mike C

01-14-2003 07:56:12

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

We have a monster wood stove in the basement, so the chimney is longer than average. With cold air in the chimney it really does not want to go up. I light a small fire to start and crack the main door ( of the stove ) open about 3/4 of an inch. When the chimney is warm it draws fine. Too much anything, paper especialy, at the start can create too much smoke and not enough draft and you know the result. Cough cough. We now have gas and a magic lever on the wall. BC Mike C

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01-14-2003 07:52:25

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

I'd be checking the flue pipe for creosote or other obstructions. Make sure the pipe is big enough and has as few bends as possible. The flue draws because of Bernoulli's Principle. With a damper open it should draw with or without heat rising through it.

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Um...

01-14-2003 08:00:42

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Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to bg, 01-14-2003 07:52:25

Not that I doubt you...but...

What does Bernoulli's Principle (the shape of an airplane wing) have to do with heat rising?

Salmoneye

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01-14-2003 08:38:05

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Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Um..., 01-14-2003 08:00:42

Bernoulli's principle was postulated before airplane wings were invented. It basically states that when the velocity of a fluid(in this case, air)increases, the fluid pressure at right angles to that flow decreases. This is why two boats traveling the same direction in water will tend to be drawn together when they get close enough that the water between them begins to move faster. This is also how a venturi works, why an atomizer or airbrush works, why airplanes fly. The movement of air across the the top of a chimney flue decreases the pressure at right angles to that flow of air. Since the air in the flue is contained, it is drawn toward the air flow at the top of the chimney, creating the draft, which creates negative pressure inside the building. My woodstove draws really well. But, when I open the door to fetch more wood, the negative pressure is relieved and if the stove doors are open, I get smoke inside the house.

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Dave in Mo

01-15-2003 05:25:09

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Re: Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to bg, 01-14-2003 08:38:05

Technically, no one knows why an airplane flies.
P1V1=nP2V2 accounts for typically about 25% lift of an airfoil. It has much more to do with the rotation of the fluid flow in the boundary layer, of which there are 3 types. Laminar flows are the furthest from the surface and effect Bernoulli's equation. Turbulant airflow are next to the surface and rotate and account for the most "lift". Between the 2 flows is called the "transitional" zone. First law of Aerodynamics is "you can fly a brick if you have a big enough engine"!

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Ah...

01-14-2003 09:48:41

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Re: Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to bg, 01-14-2003 08:38:05

Thanks,

I understand your point now. I knew about the effect in the other systems you mentioned, but just never thought of applying it to a chimney.

I still say that in a chimney or stove pipe, heat rising is far more important than any effect Bournoulis' Principle may have on draft...

What if there is absolutely no wind?

;-)

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Jim WI

01-14-2003 10:12:22

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Re: Re: Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Ah..., 01-14-2003 09:48:41

Then it smokes a while? It's not often that you'll see a dead calm at chimney height but when it happens, then you are depending solely on the temperature differences to establish the draft.

This is also the "why" behind the rules about the chimney having to be taller than the closest part of the roof. If it's not, the roof will "shade" the chimney from the wind.

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Les, TN

01-14-2003 08:35:23

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Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Um..., 01-14-2003 08:00:42

Well, Bernoulli might git involved if there's much o that black gunky stuff in thar.

Nah, he never saw a stovepipe.

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Willy-N

01-14-2003 06:44:50

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Not a expert but I have been heating with wood totaly for 19 years. I found you need to have your stack higher than the ridge or at least higher then the pitch 10 ft or so from it. I do not have the problems you are having unless my stack is getting dirty with soot. When I see back draft problems I run a brush down it and it goes away. I light mine with a egg carton under some dry wood and it fires right off. Of corse I do not let mine go out till spring gets here or it will get cold in the house as it is my sole source of heat. My stove is air tight and around 15 years old getting ready to re-place it next year and put the old one in the shop to use. Mark H.

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Luc 8N46492

01-14-2003 06:15:27

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Try this web address. The guide is called "A guide to residential wood heating", it is excellent to explain the physics of backdraft.

http://www.rescer.gc.ca/prod_serv/index.asp?CaId=127&PgId=722

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Jim

01-14-2003 05:27:29

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Open a window in the room before lighting the stove. I found that this works.

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Murray

01-14-2003 05:01:13

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Hi 9n'er, you have probably received the correct answer'(s) for your wood stove vent problems. Placing a few sheets of crumpled news print paper in the stove and setting it on fire to warm the chimney before the actual starting of placing in your wood should eliminate the problem. Also when preparing to light your fire the sheets of discarded news print,roll them up rather tightly and tie in a single knot, they lay your small wood pieces on top, should work. Now after having said all of this ,have always used wood for my primary source of heat, living in a city, handle my wood 17 times from time of cutting and taking out the ashes, retired 7 years ago as a fire chief. we always received a lot of different questions on how a wood stove should operate.Let us know how things work out, Cheers, Murray

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John,PA

01-14-2003 05:38:55

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Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Murray, 01-14-2003 05:01:13

Hi Murray,
I have a question for you, if I may,Sir,

Here in Pensacola, we are decorating an office.
Subject: SMOKE DETECTORS

We are installing "tamper-proof" smoke detectors.
The models that I have selected are "approved by the fire marshal of CALIFORNIA". Therefore, I would assume that we can use these in Pensacola, wouldn't agree? Thank you.

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Murray

01-14-2003 09:48:55

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Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to John,PA, 01-14-2003 05:38:55

Hi John PA, The smoke detectors, should have the UL stamp of approval. The Underwriters Laboratories, have given approval to these once they have been tested. In Canada all items such as these would have ULC or CSA( Canadian Standards Association) You would probably find on the detectors a one inch diamater sticker with the UL stamp of approval.California laws might be different and approval by the Fire Marshall or Fire Chief might be sufficient, usually we had the guidelines we had to follow. Cheers, Murray

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John,PA

01-14-2003 10:45:32

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Re: Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Murray, 01-14-2003 09:48:55

Thank you Murray.

I haven't received the detectors, yet, however, I saw a prototype at an industrial trade show one day. It had more labels on the back of it, than I thought it needed. You must remove the apparatus from the ceiling, or wall, first to inspect its qualifications. I considered this to be a "FLAW in DESIGN".. I will have to see if the LITHUM Battery is replaceaboe, or when the lease expires, that's too bad!!!!! !!!!! !!!!! !!

John, etal.

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Salmoneye

01-14-2003 04:40:24

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

'Draft' is all heat going up the chimney...nothing more...But you knew that...Before you lay the fire...take a sheet or two of newsprint and stuff it as far back (or even more better in the base of the chimney) and light it...this will start the heat flow up the chimney before you lay the kindling and light it...You may find that you need to do the paper in the chimney thing a couple times for your specific situation...

DISCLAIMER: I only recommend this if you are intelligent, careful, and clean your chimney regularly...Those of you that have no idea what that bristley thing on the end of that pole in the shed is for, please ignore this post...

HTH

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PS...

01-14-2003 04:58:42

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Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Salmoneye, 01-14-2003 04:40:24

Or you can heat the pipe right above the stove with a propane torch for a couple minutes spreading the heat up and down it...Anything that gets the pipe warmer than the air outside above the pipe will start the stove drawing before you lay the fire...

Salmoneye

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John,PA

01-14-2003 04:18:05

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Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to 9N'er, 01-14-2003 03:50:08

Hey 99ner

All of us campers still use some sort of parlor stoves, generally of the cast iron type.

In your situation, I think that I would check the stove pipe that goes from the stove, and the chimney. If you are us'n one of those "air-tight" new types, well, you generally have to heat up the chimney a little to start gett'n the draft. We used to put a little (4in) pipe into the side of the stove pipe just above the stove. This would allow a small amount of room air to constantly flow up the chimney, thus when you want to start-up the stove, the chimney was already warm. You might try mounting a "LONDON-TOP on the top of the chimney also. They do a great job of preventing down drafts. A good "sheet-metal" man (persons) can fabricate the LONDON TOP, if they aren't "standard equipment" and longer.

Hope this helps. :)

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Ron from IL

01-14-2003 06:56:18

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Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to John,PA, 01-14-2003 04:18:05

John,

In theory, the London-top is a good idea, BUT--I had a sheet-metal fabricator friend of mine make one for me twenty years ago when I built a new earth-sheltered home. The chimney, needless to say, was brand new, concrete block with ceramic liner. The cap was galvanized metal. At first, it worked and drew like a champ. However, within two weeks, we noticed that we were getting "puffs" of downdraft. I finally pulled the cap, and the chimney was nearly TOTALLY choked off with creosote build up. There was a hole about the size of a tennis ball left in the 8" flue! We removed the cap, and never had problems again.

Maybe a ceramic London cap would work better....

Ron

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John,PA

01-14-2003 11:00:43

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Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Ron from IL, 01-14-2003 06:56:18

Well Ron, we always kept our stoves "HOT". :})

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Salmoneye

01-14-2003 11:04:42

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Re: Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to John,PA, 01-14-2003 11:00:43

Me too...

Part of having an old farmhouse and no insulation...Got plenty of trees...

;-)

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John,

01-14-2003 04:27:25

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Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to John,PA, 01-14-2003 04:18:05

I forgot for a moment, 9ner, about physics, try a small (teaspoon ful) of olive oil each night. Does wonders for me.!

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Jim (MI)

01-14-2003 05:49:26

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Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to John,, 01-14-2003 04:27:25

I burn wood in a stove in my basement. I also have a propane gas furnace. Definately don't want the furnace sucking air while trying to start the stove. I do woodworking and find that the best thing I can do when the fire goes out and the chimney gets cold is use dry wood shavings which I have available. These start easily, burn clean with very little smoke, after laying in shavings, then fine wood, then heavier wood, I use lots of balled up newspaper as close to the pipe as possible. I light the shavings and newspaper at the same time. Generally this works.
Before starting this procedure I used to do an awful lot of damage to our clothes and house.
Also if the outside is damp and above freezing it is worse.
Hope this helps. Jim

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John,PA

01-14-2003 06:18:40

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Re: Re: Re: Re: (OT) Why backdraft on a stovepipe? physics of?how to elimnate it? in reply to Jim (MI), 01-14-2003 05:49:26

Hi,
For years, after my dad installed a PROPANE space htr., in the house, we always saved the newspapers. We have approx 1ton of papers on hand.

After the "kids" leave home, even Christmas seems like another day of the week, to some GRANDPARENTS. Therefore, now I burn the day's newspapers after I read them! We use all of the "old" newspapers to POLISH the windows. REAL INK and rags!

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