Three Flue Chimneys Reversing Draft

With all the worrys about chimneys I thought I would post this.

Anyone ever see this? I have a standard three flue masonry/clay tile chimney. The center flue is for the fireplace (rarely used, maybe Thanksgiving and Christmas on occasion), one outer is the oil boiler and the oppposite is the coal/wood boiler. Under certain conditions I have noticed what seems to be the oil side back draft to the unit from outside when operating the coal boiler. I think that it has some exhaust from the coal boiler as the air is fairly warm. The only reason I discover this is because I am a smoker (read idiot ) and do not smoke inside my home. However in the basement, I found that I could have a quick smoke and keep the smoke out of the house by tipping the barometric flap on the oil burner and puff away while the chimney does it's job and removes the smoke. Then I noticed a few years ago that at times (usually cold w/boiler cranking) that when doing so I was met with a blast of hot air in the face. It doesn't seem to feed any thing back if the flap is closed and the boiler is always live and up to temp so I'm not sure if it is coal boiler exhaust or just hot air residing there. Never got any CO readings from it and the "NOSE" I married couldn't smell anything, so I guess I was safe. Even a very short extention or cap will break this "recycle" loop. But I just want everyone to know even a GOOD chimney can kill you, if you have two or three flues check it out!

Hi Ian, you must have a fairly tight house, good windows, and good doors. Have you checked to see if the clothes dryer, kitchen stove exhaust fan or batheroom exhaust fan is also running when you experience the draft reversal?

If possible can you route a 2" or 3" PVC pipe from outdoors to the combustion air inlet to the coal boiler?? This would be safer than adding a chimney extension. [you won't have a ladder or roof to fall off of ]. Plus you get the added benefit of reducing the infiltration [negative pressure] on the whole house.

The lack of the slight vacuum on the house and the resulting elimination of infiltration in my drafty old farmhouse is one of the great benefits I see with the outbuilding coal boiler instead of in the basement boiler.

Greg L.

.

Nope, she's a real leaker. And a window in the basement open. Not much for insulation, really bad single pane windows. In general, they missed quite a few codes for a house built in 1980. The chimney is on a single floor family room and the house is a two story garrison. I'd say the chimney is about 6' shorter than the main house but at least 16' from it. . The chimney also is in the garage so it is exterior job as well. So now we know, it's short so it doesn't have a great draft to begin with. OK lousy chimney, the stove pipe has 2 90* bends maybe 6-7' total in length.
Now this ONLY happens if it is cold outside, right now it's 62*, I have a draft a little over .01 idleing and it will never do it. But if it's cold out, say <35* and the boiler is .04 or better it may...... or may not backdraft at the oil side. And it doesn't matter about the combustion blower either. I'm not sure why it happens, and that is a pretty good jump, at least 1 1/2'. I've talked to a bunch about it and several people said it was common but couldn't explain why. It may be opening the damper that sets it off, I don't know. Like I say, anything done at the top of the chimney will cure it. Say a cap or an extension to either one of the offending liners cure the problem. I even tried a baffle made of aluminum across the chimney, and that worked fine.
My point was stuff happens, there are a zillion varibles going on with this stuff and most of us here are not "licensed & trained profesionals" so be careful, make changes one at a time if you can, and watch it when you do. The last thing we need around here is a R.I.P. thread (I think I'm feeling a little mortal in my old age ).

I agree, we certainly don't want an RIP thread, for any reason, but for sure not because of a CO mishap.

I've lost one friend to CO, and it shouldn't have happened, but did. He ran a generator in a garage, right at the garage door opening, with the garage door up. But the house was fairly tight, and there was a gap at the bottom of the garage to basement door, the furnace was running, and with the wind just right, the CO went into the basement and the rest of the house. Father, Mother, and child, all died.

So when I run a generator, I put it outside the garage, even with nothing but a very-breezy breezeway connecting my garage to the house. If a poer outage lasts more than a few hours, I fire up a 3pt pto driven generator on the little tractor, it is hooked up outside the shop, well away from the house. And it runs the whole house with ease.

So do you currently have an extension on one of the chimney flues to prevent the draft reversal?

Greg L.

.

Nope, I just put a weather cap on the coal side and that solved it. I wouldn't do it unless you push the damper flap. And it won't draft from the burner view hole. It may not be exhaust from the coal boiler, just a downdraft in general as I never smell smoke even with wood. It is warm air, but again my oil boiler is always "alive" and maybe it's just pushing the warm air from the stack out? I plan to extend the chimney a little on the coal flue w/a tile, I just haven't picked one up yet. The baffle was pretty ugly as was the stove pipe.

Oh here's another one, my baro, when it's cold out has a real low whistle to it. It popped up about 3 years ago after cleaning the stack. I can actually read the draft now from the sound when I go down the cellar stairs!

Local paper today says a prominent business man and his GF found dead in home he's renovating. Faulty popane heater exhaust pipe was the cause.