No draw on woodstove

[bert0168]

This isn't my stove but I'm posting for an acquaintance with this problem.

They have a clear liner (I think it's 6") on a split level so it's less than 20' of liner. Even with preheat, they can't seem to get the stove to draw properly without really babying the fire.

Any ideas on what would cause this or what to specifically look into to resolve the issue?

 

[dave_dj1]

There could be several reasons. Perhaps some pictures of the set up? Is the stove pipe too far in the thimble? What size stovepipe? In other words are they necking it down?
Is the lay of the land causing it? Trees, hills close to the house etc. etc.?
As I said, could be a ton of things.

 

[Fred Wright]

Basic troubleshooting: Crack open a window or door and see if the draft improves. Also, I'd suggest a look in the flue. If it needs cleaning or there's creosote clogging the cap screen, that would cause it.

 

[bert0168]

There could be several reasons. Perhaps some pictures of the set up? Is the stove pipe too far in the thimble? What size stovepipe? In other words are they necking it down?
Is the lay of the land causing it? Trees, hills close to the house etc. etc.?
As I said, could be a ton of things.

Basic troubleshooting: Also, I'd suggest a look in the flue. If it needs cleaning or there's creosote clogging the cap screen, that would cause it.

All good questions that I think we looked into. I was told that prior to the liner, it used the square terracotta liner which I believe is 10 x 10 and they had issues then. So it being necked down doesn't seem to apply.

The flue was just cleaned 3 days ago and there was almost nothing in it. There is also no screen currently. The pipe goes up, into a 90 then into the wall and connects to the liner with another 90 then straight up and out.

No overabundance of trees. The roof is fairly flat and the top of the pipe is about 2 1/2 to 3' above the roof line at the wall.

Crack open a window or door and see if the draft improves.

I'm interested to know if this works. I'll get him to try it. Why would it improve the draft?

 

[Mac88]

This is probably not worth asking, but how hot are they running that stove? It takes a fairly hot fire to makes a stove draw properly, especially with restrictions (elbow in this case) in the stack. Just wondering.

 

[bert0168]

This is probably not worth asking, but how hot are they running that stove? It takes a fairly hot fire to makes a stove draw properly, especially with restrictions (elbow in this case) in the stack. Just wondering.

I asked that too. They claim that once they get it going, they keep it hot. I have not seen so I don't know what they consider hot. They claim the sweep that was there could actually feel the air getting sucked down from the top of the flue

 

[Mac88]

I asked that too. They claim that once they get it going, they keep it hot. I have not seen so I don't know what they consider hot. They claim the sweep that was there could actually feel the air getting sucked down from the top of the flue

They don't by any chance happen to have an exhaust fan (like a range hood or bathroom vent, or even a clothes dryer) running somewhere in the house do they? Something has to be creating that "reverse" air flow.

 

[imagineero]

some good posts already, you can use incense, or anything that creates smoke as an aid to trouble shooting drafts. With the fire not running, put a stick of incense near the flue. Is it running up, or is the air sucking it somewhere else? Follow the smoke, wherever it goes in the house. There may be a draft running under the house if it's up on pilons, or some other thing creating a vaccuum in the house. Remember; air is sucked, not pushed.

The height of the flue can be another possibility. Having a hot flue helps, but air running over the top creates a venturi which pulls air up by its lower air pressure. Even though the flue is above the roof line, it may be in the wind shadow of something. It may need to go higher above peak of the roof line to get wind. Pics always help.

Shaun

 

[trophyhunter]

The roof is fairly flat and the top of the pipe is about 2 1/2 to 3' above the roof line at the wall.

The elbow where it initially 90*s and connects to the horizontal section that passes through the wall, make sure the horizontal pipe has a minimum of 1/4" rise per foot before it 90's or T's back vertically and heads up. Wall pass through's are draft killer's just by their very nature.

Overall chimney height is really critical in these installations, some additional height would *help* the drafting situation, rarely will these types of installations be problem free and they always work better in the colder months of the season when the top of that stack is terminating into cooler air.

Draft issues can be really annoying when your stoves smokes you out of the house, but there's really two main factors to look at when trouble shooting.

The hotter the gas temperatures are in the chimney compared to the air outside, the stronger the draft will be. Secondly, the more overall height a chimney has will determine the amount of draft it will produce at various temperatures. You have everything to gain in a problematic draft scenario by adding another three feet of height and making sure your burning the stove at reasonable operating temperatures.

 

[Shmudda]

Do they have a cap installed on the bottom of the tee outside at the clean out?

Craig

 

[PEKS]

Other than the mechanical trouble-shooting suggestions made..
Is it more prone to occur during cold, damp or windy conditions..
The weather is a major factor with a 20 foot stack and the cold air pushing down..

 

[bert0168]

I like how this is progressing, some things in here I hadn't considered and some new investigations to try. I'll try to respond to what I know:

They don't by any chance happen to have an exhaust fan (like a range hood or bathroom vent, or even a clothes dryer) running somewhere in the house do they? Something has to be creating that "reverse" air flow.

some good posts already, you can use incense, or anything that creates smoke as an aid to trouble shooting drafts. With the fire not running, put a stick of incense near the flue. Is it running up, or is the air sucking it somewhere else? Follow the smoke, wherever it goes in the house. There may be a draft running under the house if it's up on pilons, or some other thing creating a vacuum in the house. Remember; air is sucked, not pushed.

I thought about this after I posted about the sweep finding the down draft suck at the exit. We'll try this to see if there is something running the air out. I don't think there is anything mechanically exhausting the house but I'm not sure.

The height of the flue can be another possibility. Having a hot flue helps, but air running over the top creates a venturi which pulls air up by its lower air pressure. Even though the flue is above the roof line, it may be in the wind shadow of something. It may need to go higher above peak of the roof line to get wind. Pics always help.

The hotter the gas temperatures are in the chimney compared to the air outside, the stronger the draft will be. Secondly, the more overall height a chimney has will determine the amount of draft it will produce at various temperatures. You have everything to gain in a problematic draft scenario by adding another three feet of height and making sure your burning the stove at reasonable operating temperatures.

The HO and I already talked about adding another 3' of pipe to the top to see if that makes a difference. Hasn't been done yet but in the plans. I wondered if NOT having a cap on it would cause the same venturi effect, like blowing over the top of a bottle?

The elbow where it initially 90*s and connects to the horizontal section that passes through the wall, make sure the horizontal pipe has a minimum of 1/4" rise per foot before it 90's or T's back vertically and heads up. Wall pass through's are draft killer's just by their very nature.

I was not aware of that, good thing to look into. I thought that only applied to plumbing drain pipes :hmm3grin2orange:

Do they have a cap installed on the bottom of the tee outside at the clean out?

Craig

The set up they have is a liner in an existing masonry flue. There isn't any exposed pipe other than from the stove to the wall and the 8" sticking out at the top of the masonry chimney.

I'll try to get some pictures this week but nothing jumped out at me from what I saw, other than needing a bit more height on the flue. (I think this may be their issue with the flatter roof)

I'm also wondering if the stove pipe and the liner don't meet. Meaning that if the stove pipe isn't in far enough before the flue turns up and the liner was only pushed straight down, there might be a section at that area where the smoke fills the flue but doesn't have a continuous path to the liner.

 

[bert0168]

Other than the mechanical trouble-shooting suggestions made..
Is it more prone to occur during cold, damp or windy conditions..
The weather is a major factor with a 20 foot stack and the cold air pushing down..

Their claim is that this happened before the liner was installed in the masonry flue as well, basically since the stove was put in.

I hadn't asked about outside temps but my impression was that it occurred all the time.

 

[trophyhunter]

Colder outside air temperatures and windy conditions are absolutely in your favor when it comes to draft issues, both will cause an increase on a system that typically drafts poorly, or any well functioning one for that matter. Windy conditions that induce a down draft are due to improper chimney height allowing wind to be diverted back at the top of the stack from being to near a horizontal point of contact.

The old guidelines of the 3'/10' rule of minimum chimney height which mandates 3' height from the tallest area where a chimney passes through the high side of the roof pitch and 10' horizontally to the nearest point of contact on the roof slope were a pretty good starting point for most straight up installations, in the case of a wall pass through i used a different criteria for total height.

For new wall pass through installations I was measuring 2' down from the top of the pipe and then maintaining a 10' horizontal clearance to the roof slope. It proved to be a superior method than the 3/10 rule on every single installation that otherwise fell into the 3/10 parameters yet were drafting poorly.

 

[gapl1953]

Two suggestions I haven't seen covered.
1) Get one of those magnetic flue thermometers and stick it on the flue pipe and see what the temperature is like. Most have a range on them that indicate where the flue temperature should be. I don't run my stove without one.
2) open the door on the stove just a crack to see if that improves the flow.
My dad had a problem with his stove all of a sudden. I inspected it and found that he had replaced the door seal with a better one which was thicker. The better seal was too good and the stove wouldn't flow correctly. Had to remove the seal and replace it with a thinner one so air could be drawn pass it.

I know that trophyhunter has already mention this but it is easy to miss so I will mention it again. Simply make sure that the horizontal sections of the flue pipe always angle up in the direction of the draft. If they are level or even worse if they angle downward in the direction of the draft you will have at best a no draft situation, to a reverse draft if angled the wrong way. You would have a difficult getting the fire hot enough to overcome this problem.

Greg

 

[sunfish]

They don't by any chance happen to have an exhaust fan (like a range hood or bathroom vent, or even a clothes dryer) running somewhere in the house do they? Something has to be creating that "reverse" air flow.

Our stove has a strong draw, it'll suck the wig off an old lady.

But If I try and start a fire when my wife is cookin and has the exhaust fan on, it's a no go. Also if the fire isn't good and hot, the exhaust fan will pull smoke out of the stove. We usually have to leave a window cracked.

 

[Fyrebug]

Stove Thermometer approx 18" above the Stove. Need pics of stove and install.

What is moisture content of wood? (my/their wood is dry doesnt count). Cheap moisture meter are Lowe's will soon tell him the story there. If above 20% too wet.

 

[Mac88]

Our stove has a strong draw, it'll suck the wig off an old lady.

But If I try and start a fire when my wife is cookin and has the exhaust fan on, it's a no go. Also if the fire isn't good and hot, the exhaust fan will pull smoke out of the stove. We usually have to leave a window cracked.

It happened to us. Our stove is in the kitchen and we (usually) always keep a kitchen window cracked. It warmed up a bit so we let the fire go out. Closed the window to conserve heat. Well, duh, forgot we had an exhaust fan running in the cellar where we're drying some lumber. When we next fired the stove it was a no-go. It took a bit before we remembered the cellar fan. Cracked the kitchen window and we were good to go.

 

[rmount]

They claim the sweep that was there could actually feel the air getting sucked down from the top of the flue

Sounds like they have negative pressure in the house. Bathroom exhaust, dryer, stove exhaust or something is sucking all the air out of the house and bringing more down the chimney to make up the loss. Opening a window provides that extra air and lets the stove draw, not a permanent solution but good for troubleshooting.

 

[rmount]

I should read the other posts before replying since my neg. press. suggestion has been well covered already :bang: