Draft Troubles

[wolfe]

Have come from the boiler room, as suggested I am here. My question is this, I have installed a wood boiler inside, the flu size is 6 inch.
2-45s 1-section of pipe in between, boiler has a damper. I have a down draft issue, smokes when I open the door, when boiler is not in operation downdraft into the house the smell of creosote. The 6 inch is plumbed into a 8 inch stainless uninsulated chimney with air space and a sealed top. The stainless is inside a brick masonry chimney approximatley 32 feet tall on the outside of our home. It is 15 to 20 feet from the peak, and 3 foot above the peak.

In order to start a fire I have to burn paper in the clean out to warm the flu I assume. I have been burning wood for 30 years plus. This is the first time I have experienced this, and the first time I have ever had 6 inch to 8 inch. Someone had mentioned no pressure in chimney? If the basement window is open I dont have the stink trouble. What the heck??? Anyne got an idea????

 

[ansehnlich1]

Hey, sounds like you might be sufferin' from the "stack effect". Click this link for some possible answers:

http://www.thechimneysweep.ca/2stackeffect.html

Going from 6 to 8 inch ain't the best, would be better to run 6 all the way to the top, combine that with 30+ feet of cold exterior masonry surrounding your uninsulated pipe and ya got a recipe for trouble.

Put that wood burning appliance in the basement and you add to the difficulty.

The house itself actually becomes a better "chimney" than the chimney, pulling cold air down the exterior chimney, crazy ain't it?

Look out for other appliances that may be drawing air down your chimney too, like, dryers, range hoods, bathroom fans, etc.

Good luck.

 

[jtp10181]

Not the stack effect... its negative pressure. The basement has a lower air pressure than outside. This is normal. Yours must be to the point where air is trying to get in there any way it can. The boiler flue is apparently a good way. To fix it...? Fix the makeup air system on your HVAC ducting. There is a simple little thing you can use but I can't remember who makes it. Basically you cot a hole in the wall in the basement and put a tube in with a filter on it. It lets air in as needed.

 

[LLigetfa]

Not the stack effect... its negative pressure. The basement has a lower air pressure than outside...

HUH? How is that NOT stack effect?

Stack effect is warm air rising and escaping and no replacement to make up for it.

 

[LLigetfa]

If the basement window is open I dont have the stink trouble. What the heck??? Anyne got an idea????

You have warm air leaking out of the house upstairs from stack effect. You don't provide enough "makeup air" to compensate for what is leaving the house.

The first thing to do is determine where air is leaving the house allowing for a negative pressure and reduce those losses. Since warm air leaving is not as easy to notice as cold air entering, many people seal only the cold drafts and this only makes things worse. Find where the air leaks out with a smoke pencil and seal those. Allow enough fresh air in to compensate for other losses like exhaust fans and your problem should be solved.

 

[ansehnlich1]

The "stack effect" causes negative pressure in the lower area of the home. That is why opening the window improves the situation. Providing air to the appliance would surely help in it's function.

Many things can compound the problem. I mentioned a few previously. If you have an oil or gas furnace that runs at the same time your wood appliance is running, that in itself may be enough to tip the balance.

http://en.allexperts.com/q/Chimney-Fireplaces-3286/smoke-1.htm

http://www.woodheat.org/technology/bpfireplaces.htm

http://www.thriftyfun.com/tf640117.tip.html

 

[jtp10181]

Not the stack effect... its negative pressure. The basement has a lower air pressure than outside...

HUH? How is that NOT stack effect?

Stack effect is warm air rising and escaping and no replacement to make up for it.

I just now read the thing posted above and I guess I never saw the Stack Effect explained that way (guess I never fully understood the term). Makes total sense. Guess the second posted and I were talking about the same thing.

 

[Todd]

Negative pressure in the basement. Can you hook up outside combustion air to the boiler? If not look up the Condar Air Supply Ventilator.

 

[jtp10181]

look up the Condar Air Supply Ventilator.

That's the "simple little thing" I was talking about earlier. Although the best solution would be a combo of that plus what another suggested, which is finding the leaks in the top section of the house that is letting the air out.

 

[wolfe]

I have a 2 inch air induction on the left side of the boiler, I could do a outdoor intake run directly to it. It has a small damper in it. That would help, however the automatic damper then will still operate but I wonder if this would be to much air injecting? You know burning to much to fast I guess trial & error..

 

[Todd]

I think 2" may not be enough? Most OAK's for wood stoves are 3 or 4". But I'm not very familiar with wood boilers. Does your manual have any info on this?

 

[oconnor]

Try the outdoor air kit (OAK) hookup. At least then, when your boiler isn't running, there would not be as great a potential to reverse flow, as the system will be connected at both ends to outside pressure. As well, the flue will not try to draw cold air from the basement, agrevating any possible stack effect.

Check the manual regarding an OAK hookup. I can't imagine it being a problem logically, but I didn't design your boiler

Also, make sure that you don't have other exhaust sources running when you start the boiler fire (bath fans/clothes dryer/range hood vented outside). Each of these uses more air than a modern EPA stove, and possibly more than your boiler. That would make the reversal more difficult to "reverse".

Also, if you have a loose fitting attic hatch or other "passive" vents (roof turbine that is drawing air from inside the heated house envelope), shut them down. I have actually caulked my attic hatch shut - not like I need up there often.

Give the link in my signature a read - Guide to residential wood heating (ch 10 in particular) to get an overview on the "house as a system of systems" and how many different things can affect draft. Good explaination of Stack effect, mechanical depressurization, wind effect, etc.