House too tight or leaking 2nd floor?

[SIERRADMAX]

I keep fighting a downdraft with a 3 flue exterior 35'+ tall masonry chimney. I know it's not ideal to have an outside chimney but it was built after I bought the house. One 8x8 clay flue serves the oil boiler in the basement, one 8x12 serves a wood boiler in the basement and another 8x12 serves a woodstove on the main floor of the house. Clay flues were wrapped with roxul and I have 1 S.S. cap covering all 3 flues (w/ SS baffles between exiting flues).

House is a 2001 built 2-story 2600 S.F. with a full basement. Center stairwell, Hydro-air for HVAC. House has vents in the floor (first floor) & vents in the ceiling for the 2nd floor. 2nd floor has bathroom vents, a sealed attic hatch, & a couple insulated recessed light fixtures. Typical 2x construction, 5/8" plaster drywall, tyvec wrapped & vinyl sided. Vinyl windows & doors.

First scenario.... Wood stove going on the main floor, smoke smell omitting from the openings (Barometric Damper primarily) from the wood boiler (not in operation) in the basement. So, the cold flue serving the wood boiler is pulling smoke down from the adjacent flue serving the wood stove. This would leave me to believe that my house is relatively air tight. That the wood stove on the main floor is pulling combustion air from the basement via the wood boilers baro.

Second scenario... Very cold outside and wood boiler is in operation. After 3-4 days of continuously using the WB, I started noticing a smoke smell omitting from the oil boilers baro. I ended up cracking a basement window slightly and the smoke smell became less severe.

Finally, we have had 2 days with weather above 40. Sunday morning, I shut the WB down to do a cleaning & closed the window in the basement. 2 hours later, I decided to light a fire in the wood stove. I normally warm the stovepipe a little with a torch but to my dismay, it had such a downdraft that the flame was "mushrooming" across the torch head. The stovepipe was unusually colder than normal. I ended up re-opening the basement window, opening the cellar door and waiting 15 minutes. Sure enough, I was able to get it going. This to me, would indicate that the house was creating a strong stack effect (leaky 2nd floor). But could it have been possible that the wood boiler (below) was sucking so much air that it was also pulling through the wood stove on the main floor? This would lead me to believe that the house is relatively tight.

 

[Backwoods Savage]

It is common to have this problem with a 2 or 3 flue system. Most will put an addition onto the wood stove chimney to get it above the others and this tends to take care of the situation.

On the downdraft and starting a new fire, you very well may have to resort to heating up the chimney before starting the fire. You can do this by lighting some paper, using a torch or even using a hair drier. The idea is to get heat in the chimney to reverse the flow to going out rather than down.

Good luck.

 

[HotCoals]

I'll never understand why someone would use air to move hydro heat around.
I guess if you have to do it because the hot water base board was not built with the house.

 

[HotCoals]

Are all 3 stacks the same height?
I'm also curious if the wood boiler is a pressurized system?

 

[begreen]

Are all three flues terminating at the same height? If so, this product could help:

http://www.extendaflue.com/products/extend/extend-a-cap.html

 

[samiamrd]

I think that your down draft is due to several things. First you have a cold outside chimney. That lowers the draft potential in your chimney. Second your in the basement which is the lowest pressure place in your house. That is because as the air heats up, it rises in the house and it must be replaced by something and in this case it is your flue that is doing this. Opening the window helps, but that wont help you when the draft collapses at the end of the fire. That is a potential huge problem. You already know that your pulling in exhaust products. That is bad and dangerous.

Another concern for me is the size of the flues. The oil boiler flue is probably the right size, but the flues for the wood stove and the wood boiler are too big(way too big). Having a flue that is too large, slows down the up draft in the chimney and leads to additional cold flue problem. What may help with your house is to put a stainless steel liner which is the size of the outlet on your wood stove in your wood stove chimney. That will create a better draft for your wood stove and keep your chimney hole for the wood stove slightly warmer than the cold clay liner. You should also do this for the wood boiler in the basement. That will help the wood boiler and create a better draft in the chimney that you have. Right size flues do work. Read this on chimney liners. (http://www.woodheat.org/attachments/article/bplinerusers.pdf) Also read this about chimneys and how they work (http://www.woodheat.org/all-about-chimneys.html ).

 

[SIERRADMAX]

Are all three flues terminating at the same height? If so, this product could help:
http://www.extendaflue.com/products/extend/extend-a-cap.html

Yes, all 3 terminate at the same height. Never thought about extending the flues. I'm surprised the guy who built my chimney didn't mention varying heights. All 3 are covered by one Stainless Steel Cap. I did add stainless baffles between the exiting flues but I suspect this only alleviated a little bit of the problem.

I think that your down draft is due to several things. First you have a cold outside chimney. That lowers the draft potential in your chimney. Second your in the basement which is the lowest pressure place in your house. That is because as the air heats up, it rises in the house and it must be replaced by something and in this case it is your flue that is doing this. Opening the window helps, but that wont help you when the draft collapses at the end of the fire. That is a potential huge problem. You already know that your pulling in exhaust products. That is bad and dangerous.

Another concern for me is the size of the flues. The oil boiler flue is probably the right size, but the flues for the wood stove and the wood boiler are too big(way too big). Having a flue that is too large, slows down the up draft in the chimney and leads to additional cold flue problem. What may help with your house is to put a stainless steel liner which is the size of the outlet on your wood stove in your wood stove chimney. That will create a better draft for your wood stove and keep your chimney hole for the wood stove slightly warmer than the cold clay liner. You should also do this for the wood boiler in the basement. That will help the wood boiler and create a better draft in the chimney that you have. Right size flues do work. Read this on chimney liners. (http://www.woodheat.org/attachments/article/bplinerusers.pdf) Also read this about chimneys and how they work (http://www.woodheat.org/all-about-chimneys.html ).

I agree that the wood stove flue is oversized. I plan on adding a liner this summer. However, I don't think the wood boiler flue is. It pulls like a mule when warmed up.

 

[JV_Thimble]

It is common to have this problem with a 2 or 3 flue system. Most will put an addition onto the wood stove chimney to get it above the others and this tends to take care of the situation.

On the downdraft and starting a new fire, you very well may have to resort to heating up the chimney before starting the fire. You can do this by lighting some paper, using a torch or even using a hair drier. The idea is to get heat in the chimney to reverse the flow to going out rather than down.

Good luck.

I have the occasional downdraft when the stove is cold with a two story, single flue, insulated system. I'll try preheating with a heat gun when I can feel cold air coming down - prior to startup, of course.