Air back-flowing from chimney when stove is off.

[PlayWithFire]

I have a Vermont Castings Vigilant 1977 in my basement next to an oil fired boiler. They go into separate ceramic flues. I only use the basement wood stove a few times a year. Sometimes I notice a strong creosote smell in my basement which is caused by air back-flowing down the wood stove chimney into the basement. I notice this most in the spring and fall with the outside temp is similar to the basement temp.

I need some help with a solution.
I'm not sure if this is caused by the oil fired boiler sucking air down the wood stove flue or just some-kind of natural convection when the inside and outside temps are just right. For example this morning the outside temp was 44, basement was 55, and the creosote smell was over powering.

Make up air?
I will say that after foaming the sill plate, adding a storm door to the walkout basement door and weather stripping to the door to the rest of the house, I have a very 'tight' basement. Do I need makeup air for the oil burner and wood stove? If so how do i connect the outside air to these appliances?

Thanks in advance!

 

[begreen]

Basements are notorious negative pressure zones. When the oil boiler comes on it increases the negative pressure as it consumes air for combustion. Other exhaust fans in the house will also exacerbate the situation, as can leaky upstairs windows, attic doors and recessed light fixtures. The best solution is to move the stove upstairs, especially if that is where the heat is desired. In lieu of that, supplying outside makeup air to the boiler may help.
http://woodheat.org/all-about-chimneys.html

 

[PlayWithFire]

begreen, Thanks for the comment and the link. As I have an external chimney, it looks like the issue is....
'The air in a chimney that runs up the outside of the house gets chilled, so the draft in the chimney is less than the stack effect of the house, and the chimney back-drafts'
I noticed the back-drafting issue today even with the basement door wide open. Since this surely would equalize the pressure I'm pretty convinced the above quote accuracy describes the issue.

I already have a wood stove on my main floor and this is just a backup for the really cold days. So, it's staying put... Does anyone know of a good/easy way to block off the flue without removing the stove pipe?

 

[begreen]

Is there a key damper that can be closed in the stove pipe?

 

[PlayWithFire]

there isn't a key damper and it looks like the only ones that are sold now are not solid and still let air through.

 

[vasten]

It sounds to me like you need to run that stove hotter than you maybe running it currently, and allow more heat up the chimney to increase draft. The warmer it is outside. 40-50's the draft on any chimney is decreased.

For example this morning the outside temp was 44, basement was 55, and the creosote smell was over powering.

I would suggest experimenting with running the stove in updraft mode vs horizontal, to throw more heat up the chimney and see if that alleviates some of the problem. As the temperature between the basement and outside air temps increase and the temp inside the flue increase, then the draft should naturally pick up.

If you ran the stove with the cellar doors open and it didn't change the back drafting then I would agree you eliminated the negative air pressure concern, because I doubt you can introduce more air into the basement than a door wide open.

 

[coaly]

Give the oil burner its own air intake. The induction blower and barometric damper (if one on the boiler chimney) expel air from the basement along with dryer or radon fans. A simple 3 inch PVC pipe with elbow facing upward on the inside and downward on the outside with a screen prevents warmer air inside from rising to the outside and the air pressure outside has a path of least resistance to get in. When you feel the cold air rushing into that pipe, don't fret. The same volume of air was leaking in to replace what was being exhausted except it was leaking in anywhere it could and migrating towards the air consuming appliance.
The wood stove will use that air intake when fired as well instead of pulling from any cracks or down the oil burner chimney.

 

[coaly]

It sounds to me like you need to run that stove hotter than you maybe running it currently, and allow more heat up the chimney to increase draft. The warmer it is outside. 40-50's the draft on any chimney is decreased.



I would suggest experimenting with running the stove in updraft mode vs horizontal, to throw more heat up the chimney and see if that alleviates some of the problem. As the temperature between the basement and outside air temps increase and the temp inside the flue increase, then the draft should naturally pick up.

If you ran the stove with the cellar doors open and it didn't change the back drafting then I would agree you eliminated the negative air pressure concern, because I doubt you can introduce more air into the basement than a door wide open.

The problem is when the wood stove and chimney is not in use. The wood strove chimney becomes an air intake for the house.

 

[vasten]

ah ok I was reading it as when the stove was running...sorry