Draft problem...

[Mike4673345]

My woodstove is installed on the 3rd floor of a large farmhouse that was built in the 1700s. I've had horrible draft problems since I installed it a year ago. I usually need to leave a nearby window open completely or even place a box fan in the window blowing in to keep the stove pipe from smoking. Sometimes leave the window closed if I close the air down on the stove all of the way, but the pipe will still "puff" occasionally.

Here's the setup:

1. Woodstove is a Wonderwood - not a pretty stove but has a huge firebox and can take a 27" long log. I've had it burn for 24 hours on the lowest setting.
2. Woodstove has a 6" outlet out the back and the pipe has two 90s in it before it goes into the wall, reduced down to about 4.5" to accommodate the permanent hole in the wall.
3. The chimney rises about 20' from the level of the stove. Chimney has been cleaned and checked.
4. We are in a very windy area, almost on top of a hill, but the wind often blows from the top of the hill down towards the house. Watching the smoke come out of the chimney, it often changes direction radically and almost never goes straight up.

I just recently learned that the fireplace on the first floor is most likely using the same chimney as the woodstove, and the flue down there is usually left open. I'm thinking this is causing most of my draft issues with the stove.

My original idea was to try a vacu-stack on top of the chimney to help block any wind and pull the smoke up the chimney, but I'm thinking that will be ineffective if the flue is open on the first floor, as it will just pull air from there instead.

Thoughts?

Thanks,

Mike

 

[Corey]

How tall is your stove flue? That will be one big key. I have a ranch house and the flue is only about 13 feet to the top of the chimney. That is marginal on the warmer and especially rainy days. I added a 5 foot length of stovepipe and it made a huge difference.

Another key is how many bends / how clean is the pipe? Every year we have a post or two about someone finding a big lump of creosote, leaves, a bird, a squirrel, or what ever else clogging up the flue. Once the obstruction is cleared, draft is restored. Older stoves are especially prone to creosote. Just a 1/2 inch layer of material on a 6 inch pipe will cut the cross sectional area by 1/3. That will cut draft substantially, even if it is just a build-up in the last foot or so of pipe.

I would also say try it with the downstairs flue closed and sealed - you have a three story tall flue trying to pull air out of the house there, and I estimate a 1 story tall flue up on the third floor. We know taller flues draft stronger, so the one on the bottom floor is winning.

Also look for any vents, basement/cellar stairs, etc which may be draining cold air out of the house. These will act like a 'reverse flue' creating a downdraft and also make it harder to draft upward.

 

[Mike4673345]

The stove pipe comes out of the back of the stove about 6" to a 90, which goes up about 6" to another 90 which goes into the wall about 30" away. I thought about raising the entire stove up to the level of hole in the wall to eliminate both 90s, but I'm not sure that would be safe. The floor in the room is not very level, so I would need a very wide base to set the stove on. From the hole in the wall to the top of the chimney is probably 15-20ft. I agree that adding to the height of the chimney would help, but this is a historic property so we need to keep aesthetics in mind. I was even going to get a copper colored vacu-stack if I go that way.

The pipe was brand new when I installed it and I still had the problem. It does have two 90s which aren't helping. I was told that the chimney had been cleaned and checked, but we are going to check it again tomorrow. I do get a decent draft with the fan on high blowing in the window, so I don't think the pipe/chimney are too restricted if at all.

We are going to try closing the downstairs flue tomorrow to see how that affects the draft. I have a feeling it has to make some difference. The downstairs fireplace is also a much larger opening than the 5" pipe on the 3rd floor, so I suspect it draws air from there more readily.

This is also a good point I had not thought of. I have gone to great lengths to draft-proof the windows on the 3rd floor (my apartment) but I don't think the same has been done downstairs, so it could more easily be pulling air in from down there, as the house is typically very drafty. I've played with the idea of bringing in a fresh air line from one of my windows to the woodstove, might have to try that. I've also noticed that if I leave my window open without the fan on, the wind will blow strongly in the window one moment, but then strongly OUT the window the next! You can imagine what this does to the stove...

Thanks for your input.

 

[Corey]

Coffee has kicked in and I am reading better now!

You say 'two 90's' - which is true, then the pipe goes into the wall, and the smoke has to make a bend to go vertically - so that would technically be a 3rd 90. I think the rule of thumb is each 90 effectively cuts 2-3 feet off the equivalent draft. ie your 20 foot flue drafts like an 11 foot flue due to the three 90 degree bends the smoke makes. The medium length horizontal run also doesn't help. Then I notice you say the pipe is reduced to 4.5 inches to get through the wall, that is another huge reduction in draft.

You also mention the stove going into a 'chimney' and the fireplace downstairs using the same 'chimney'. For clarity, it's important to differentiate between chimney and flue here. Chimney generally being the big overall structure which can hold multiple flues, with a flue being the hollow tube / pipe where smoke passes.

So based on that, it would not be such a big deal if the fireplace and stove used the same chimney, but if they use the same flue, that is a huge issue. In that case, when the smoke from your stove gets into the common flue, I'm sure it would much rather pull air through the open fireplace than through three 90 degree bends, a 4.5inch restriction and what ever air control the stove has. So what ever flue the stove is on, it needs to be sealed tight so any rising smoke pulls a draft directly through the stove and not through some other opening such as the fireplace, a clean-out, loose mortar joint, etc.

If it IS a common flue, for safety, I will also mention the potential to have CO back-up or reverse flow as the stove burns down to coals, so I would say get a good CO monitor for both downstairs and upstairs and take what ever actions are necessary to fix this issue. Ideally, remove the 4.5" restriction and make sure the stove is on it's own flue which is sealed to the stove itself.

 

[begreen]

A picture would help clarify the description. It sounds like there are 4 or 5 issues here. Let me know if I have these correct.

1. three 90 deg turns in the smoke path
2. an illegal restriction of the flue pipe down to 4.5"
3. an appliance attached and sharing a fireplace flue
4. the dilution of draft (and flue temp) by the sharing of the chimney
5. and probably dumping into a too large chimney

Sounds like risky business. In addition to having multiple errors this setup sounds like a creosote factory. Has this also been an issue? How frequently is the chimney being checked for buildup?

 

[Mike4673345]

I was told just yesterday that it may share a common flue, I will verify this tomorrow as it's not an easy task to get onto the roof of this building. I didn't even think this was possible given draft and smoke issues, but maybe that's how they did it 200-300 years ago.You have everything else correct.

I agree that CO detectors should be added, I'll pick up some.

The 4.5" hole goes into what used to be a fireplace on the third floor but at one point was all mortared up and painted (not sure what they filled the space with) with just the 4.5" stove pipe hole left. It's not an option to enlarge the hole at this point, but that was my very first thought when I installed the stove. Trust me, I did NOT have a good feeling going from 6" down to 4.5".

Coffee has kicked in and I am reading better now!

You say 'two 90's' - which is true, then the pipe goes into the wall, and the smoke has to make a bend to go vertically - so that would technically be a 3rd 90. I think the rule of thumb is each 90 effectively cuts 2-3 feet off the equivalent draft. ie your 20 foot flue drafts like an 11 foot flue due to the three 90 degree bends the smoke makes. The medium length horizontal run also doesn't help. Then I notice you say the pipe is reduced to 4.5 inches to get through the wall, that is another huge reduction in draft.

You also mention the stove going into a 'chimney' and the fireplace downstairs using the same 'chimney'. For clarity, it's important to differentiate between chimney and flue here. Chimney generally being the big overall structure which can hold multiple flues, with a flue being the hollow tube / pipe where smoke passes.

So based on that, it would not be such a big deal if the fireplace and stove used the same chimney, but if they use the same flue, that is a huge issue. In that case, when the smoke from your stove gets into the common flue, I'm sure it would much rather pull air through the open fireplace than through three 90 degree bends, a 4.5inch restriction and what ever air control the stove has. So what ever flue the stove is on, it needs to be sealed tight so any rising smoke pulls a draft directly through the stove and not through some other opening such as the fireplace, a clean-out, loose mortar joint, etc.

If it IS a common flue, for safety, I will also mention the potential to have CO back-up or reverse flow as the stove burns down to coals, so I would say get a good CO monitor for both downstairs and upstairs and take what ever actions are necessary to fix this issue. Ideally, remove the 4.5" restriction and make sure the stove is on it's own flue which is sealed to the stove itself.

 

[Mike4673345]

Correct, a total of three 90s. (correction, just looked again and at one point I had adjusted each 90 to be a 45, so I really have two 45s right on top of each other in the pipe, then the 90 inside the wall to the chimney) Yes, the 4.5" restriction sucks but I can't do anything about that right now, see previous post. Very possible a fireplace below is using the same flue, will verify tomorrow. Had I known about this previously, I wouldn't have even tried to light a fire in my stove. Going to measure the inside of the chimney tomorrow anyway for possible vacu-stack, can't tell at all how big it is from the ground.

I also thought about the creosote, as the stove must be run cut back to very little air at all times. The stove was only run last winter like this, I was told the chimney was cleaned before that. We will check the chimney tomorrow for buildup. I realize this is not a good setup, but I'm stuck with certain limitations to try to make it work. Even with the stove running but with air cut all the way back, it got pretty cold up here last winter, so I really need to make it perform better. Not fun having to sit on a heating pad while at the computer. The other source of heat in the house is steam radiators, which will sweat you out when they are running, but freeze you out when they aren't. Thermostat is in another apartment on a lower floor.

Thanks for your input!

A picture would help clarify the description. It sounds like there are 4 or 5 issues here. Let me know if I have these correct.

1. three 90 deg turns in the smoke path
2. an illegal restriction of the flue pipe down to 4.5"
3. an appliance attached and sharing a fireplace flue
4. the dilution of draft (and flue temp) by the sharing of the chimney
5. and probably dumping into a too large chimney

Sounds like risky business. In addition to having multiple errors this setup sounds like a creosote factory. Has this also been an issue? How frequently is the chimney being checked for buildup?

 

[begreen]

It sounds like the safer and long term more practical solution would be to zone each apartment on its own thermostat.

 

[Mike4673345]

I agree that would be a good solution, however this is a very old system and very old house, so that might not be practical. To my knowledge it's not zoned at all right now. We looked into one of those chimney fans, but they appear to be about $1500. They mount on top of the chimney and draw the draft upwards.

It sounds like the safer and long term more practical solution would be to zone each apartment on its own thermostat.

 

[begreen]

Adding a draft inducer to this problem riddled flue system is like putting in a bigger motor because the brakes are sticking. Fix the root problems. Do you own this bldg. or are you a renter?

 

[Mike4673345]

Renter.

Adding a draft inducer to this problem riddled flue system is like putting in a bigger motor because the brakes are sticking. Fix the root problems. Do you own this bldg. or are you a renter?

 

[mellow]

What did you use to reduce it to 4.5"? I am not aware of an reducer that is even made for going from 6" to 4.5".

 

[Mike4673345]

I used a reducer like this: (broken link removed to http://www.hardwarestore.com/reducer-652064.aspx) The opening could technically be a 5" but measured closer to 4.5".

What did you use to reduce it to 4.5"? I am not aware of an reducer that is even made for going from 6" to 4.5".

 

[mellow]

Look up chimney balloons, that could be put in the non-used flue and is not permanent, you can sometimes find them at Home Depot.

 

[Mike4673345]

Lol, I actually thought of putting something like that in there that I could inflate but then found out that fireplace is used regularly, although I've never had any smoke come in my pipe from it. Really need to check the flues tomorrow to see if they truly share the one flue.

Look up chimney balloons, that could be put in the non-used flue and is not permanent, you can sometimes find them at Home Depot.

 

[mellow]

Dear lord, yes you need to have this whole thing gone through by a Certified professional before burning in it again.

Look up a local sweep with NFI or NCSG or CSIA credentials and have them come take a look at this.

 

[Mike4673345]

Yes, we will take a cursory look tomorrow just to determine how everything is truly routed and then call in a pro if we decide it's worth the trouble to continue using the stove. Thanks!

 

[mellow]

Just a thought, but if the other flue can be blocked and this made safe I would look at going to a pellet stove with a 4" exhaust.

 

[Mike4673345]

When I originally saw the size of the hole, it reminded of the pellet stove I had 10 years ago. It was a good stove, but I sold it after a year. I like the independence of a woodstove, you can get wood from anywhere, and you don't need electricity for it to work, which is one of the times woodstoves are needed the most. I think pellet stoves had their place, but I already own this woodstove (and have a 2nd in storage), so I'd like to use it if possible. I also have a limitless supply of free firewood nearby...

 

[mellow]

5.5" is about the smallest one should go with when it comes to a wood stove. Unless you can figure out your chimney situation and fix those problems you might as well look for other solutions for heat.

 

[Pimp Your Slammer]

With the wind, all the 90s, more than one appliance and the restriction to 4.5, you have a number of barriers that obstruct your draft.
Rather than redesign the whole thing to accommodate all the different issues, try the one thing that will overcome them all simultaneously. An in-line fan just beneath your cap install with several speeds will guarantee your draft. Not the cheapest solution but certainly will solve everything I believe.
You wou essentially be turning your chimney into a vac chamber. Wind gusts can be difficult to overcome since they are never the same.
Once it's hot, then you choke down on the flue, turn the evacuation fan on low or off and watch it rock regardless of the position of the other flues or pipe configs. Just make sure your chimney is safe .

 

[begreen]

How safe would that be if the fireplace down below is also on this chimney?

 

[Pimp Your Slammer]

How safe would that be if the fireplace down below is also on this chimney?

My guess is, if the fan on the chimney top is sized right, air will only enter the flues on each level. I'm trying to imagine a situation that would make it not work. A starving vacuum on top the chimney leaves the smoke only one path. Unless the chimney has blockages, the carbon monoxide, from the lower and mid levels must evacuate. His wood consumption may be elevated.

 

[begreen]

The whole setup sounds illegal if both are on one chimney, especially in an apartment building where the actions of one could affect the other, possibly fatally.

 

[Pimp Your Slammer]

The chimney mason who lives my neighborhood said that it is not uncommon to have more than one device per chimney, but they have to have individual flues or liners within that chimney. Either way, they more I ponder it, the more nervous I get. I think I may find another heat source.