Back Draft

[Mike Wolak]

Back draft in my chimney.  Happens only on windy days.  I just put a screen cap on chimney to see if this resolves the problem.  It did'nt. The chimney opening is square 13 x 13.  Just a normal fireplace.  The flu is working and the chimney is very clean.  I started a fire, the heat drafts up good then when I get a gust of wind "MICHIGAN" winter, then poof, a smoke plume comes back in the family room.  On real windy days I get hardly no draft to the point that I had to remove the burning logs and throw them outside!  I looked in the chimney and no obstrutions what so ever.  Any suggestions on how to improve my draft?  Opening the window in the house did'nt work.  Thank You.

N8JGU MIKE

[crashk6]

Does your chimney extend above the roof line far enough? My first instinct is that it does not. I've dealt with many smoky chimneys that were fixed by making them a bit taller. Does the fire place have doors or an insert? That would also help keep the smoke out of your room.

--

crashK6

[Mike Wolak]

Just a screen, no doors, no insert.  The chimney is about 5 feet higher than the peak of the house. Would a liner insert help the chimney?  Would restricting the 13 x 13 diameter help?

[Oso]

They make various chimney caps that are designed to eliminate the chimney down draft. Try a google search on:   chimney wind cap

It will give you a number of hits.  The volko.com site has a good explaination of downdrafts and also dynamic wind loading which produces similar symptoms. They promote a cap called vacu-stack. It appears that it would work well, but may be a bit of an eye sore.  Personally, I think I would go with the more old fashioned directional wind cap design.

[Mike Wolak]

What is a directional wind cap?

[TomW]

Mike;

Been burning wood my whole life and occasionally used a regular fireplace. First thing is they usually actually cost you heat because they draw room air out the chimney. One thing you might check is that many of the older style fireplace chimneys have a "smoke shelf" and a flap damper. If the damper is not properly opened during burning you will get bad draw up the stack, also if the "smoke shelf" is full of ashes, creosote or a squirrels nest the same thing will happen. Another point is if the damper flap is open with no fire you are losing air up the chimney all the time.

Take a flashlight and look up in the top of the firebox as if trying to look up the chimney you may see a ring or chain or arm to activate the flapper. My first guess is you either have an obstruction or closed damper. Second thing is you probably should have a cap to both deflect wind coming down or rain. Chimneys are not rocket science but they need to be clear and have a cap or other method to deflect down draft in some locations where wind comes from above due to trees terrain or buildings. Currently we use a simple concrete slab about 12" above the chimney top which is part of the blockwork.

Cheers.

TomW

[ADMIN]

Yep, it does not hurt to make the chimney extra tall. The more draft the better, as long as your stove is airtight. BUT -- does your masonry chimney have metal stovepipe all the way up thru it, or is it just brick/rock/etc.? It has to to work correctly. If there's not metal stovepipe all the way up thru the masonry, you may have so many air leaks that you'll never get a good draft. Push real stovepipe all the way down thru, and you may be just fine on draft with your present setup. Any odd bends in your stovepipe? That will hurt too. My pipe goes up straight a total of 33 feet, thru a second story. The draft is ferocious, it's great.

My big problem here is creosote on the external mesh of my 'wind cap." If the weather is nice, I can climb up there and get rid of it with a screwdriver. If it's snowy, I have to use a CO2 pellet gun or .22 rifle. PITA. I don't get any creasote at all in my main pipe because of my burning habits, it only appears on the 'racoon + bird guard' mesh.

ADMIN

[MountainMan]

Another important aspect to draft is getting the chimney good and hot.  If all of the "air" rising from the chimney is reaching near outside temps by the time it gets to the top, then it looses its will to rise.  Maybe you just need to burn it good and hot for awhile with smaller drier wood until you get the chimney heated up good.  This will also reduce the buildup of nasty stuff inside the chimney (it won't condense on a hot chimney).

jp

(now in San Diego, but formerly of Upstate NewYork)

[Oso]

Here is a link to a directional wind cap spec sheet.

http://www.famcomfg.com/PDFOutput/WDCspec.pdf

Oso

[Mike Wolak]

Thank you for all your help, I like all the theories.  Well I'm going to get directional wind cap, burn hotter fires, if that fail, insert the chimney.  Just wanted to start a fire in the fire place to take out the chill.  No wood stove, no insert, to expensive.  But thrilled that my friends here on the Otherpower board can assist.  Thank You.

[Kwazai]

my brother has a real small and short chimney on his house and has a similar problem (low draft leakage into the room). what fixed his was to obstruct the top 1/3 of the fireplace opening with a piece of sheet metal-essentially blocking off the top third of the opening into the room. just a thought...

L8r

Mike

[nothing to lose]

"what fixed his was to obstruct the top 1/3 of the fireplace opening with a piece of sheet metal-essentially blocking off the top third of the opening into the room"

I had a comercail wood stove that had a sheet metal flap built into it like that. When I opened the door to load wood the flap held in the smoke to the top half of the burner, when the flap would get stuck raised for a few minutes the smoke would roll into the room. I had a bad draft the way I ran the pipe. I don't know if that would actually help with a down draft much though. If not much of a down draft and seldom it might work. The down draft is more like fan forced air, not just a lack of ability to rise.

Shouldn't hurt to try it if you have a piece of metal laying around.

My problem was I came off the stove with a 90, went 2' or so sideways, then 90 back up again to get out the wall through an old airconditionare shell. Not a good draft that way, but worked ok while I needed it.

I have alot of turbulent air here right next to my stove pipe because of a very big tree outside really close to it. A cap on top fixed my down draft problems there.

Only place I can put the wood stove inthe house, and I ain't about to cut down that tree either

[RickieBlue]

I would take 4 bricks and place them on all 4 sides of the top of the chimney (laid on their side) and put a concrete slab on top. I was told by an oldtimer that this is a solution that will always work well on a chimney with problems such as this. He did state that it will actually increase the draft in windy situations, as it will act like a pump and create a slight vacuum. Doesn't cost much and is certainly easy to try. Let us know if you try it out.

[jmk]

  I agree with Kwazai. I have used, or seen alot of home made or improperly built fireplaces. They have the damper to close to the opening of the fire place. The other thing is if this a newer home all wraped with house rap, taped windows before sided, and all sealed up good. There is no place to get the air for your fireplace to pull. A quick check is to crack a window and see if your problem stops. The best way to build a fire place is to have intakes at the bottom comeing from outside air. What alot of people don,t know is the rate you see your smoke coming out of the top of the chimny, is the rate of wich you are drawing in cold air from leakage at the windows and doors. A system like that is a catch 22. It feels warm from about two feet above the floor and up, and has a cold draft below. Conect outside air strait to the box and wala you can save your heat.    

[farmerfrank]

Do you have a newer,fairly tight house? Some houses are so thight that they will stuck air down one chimney when the other chimney is in use because it cant get replacement air from anywhere else.

[TimV]

This may seem crazy ,but when I was a kid we had a  fireplace that wasted a whole pickup load of wood each day(dad worked in sawmill).The only way you could keep this silly thing from smoking was to always keep the wood twoards the left hand side of the fireplace and all the way to the back of it. Worked fine if you did, if not it would smoke you out of the room. Finally we bricked the front and installed a Franklin Stove look-alike, cut the wood consumption and doubled the heat output and no more smoke!

[TimV]

LoL!!!

Co2 gun .....Yup they sure work great to brak off that nasty creosote chips.

I installed a insulated chimney a couple years ago and burn seasoned 2 years wood and still had a problem with the exposed cap getting covered with creosote and it actually caught fire once ..It looked like a big pumpkin glowing on the roof.....made neighbors very nervous and my wife also.

I shut down stove and found inside cimney was spottless and only creoste was what was on cap. ...borrowed kids BB gun and chipped off the chunks of black nasty creosote.....

My chimney is 28 feet tall and has excellent draft but the cold exposed cap is a problem I never saw coming.....