Chimney/woodstove question

[tyb525]

I think this is the best board for this topic.

We have a woodstove that is connected to an old brick chimney. The chimney is in great shape, it runs up beside our house and ends about 3 feet above the roof. It's always seemed to have a great draft.

However, last year we had a chimney fire. Luckily, it didn't last long and stayed within the chimney. Unfortunately, it was a windy day and it got real hot real fast, and apparently it cracked the clay liner up near the top - smoke was coming out between the bricks/mortar.

Because of that, we had some chimney guys put in a new chimney liner. It was the 8" flexibly corrugated metal stuff, which seemed awful small to me, but I'm no chimney expert. Anyways, now to my question.

Would this liner cause the stove to need much more air in order keep the fire burning with any kind of heat? Before the liner, we could fill the stove with wood, close the vents almost all the way, and it would stay lit and last pretty much until early morning. If we try to do that now, it either goes out or just smolders and doesn't produce heat. During the day when someone is at home to tend the fire (that person is me ;)) the vents have to be wide open to get decent heat, and it goes through wood almost twice as fast (I also cut the firewood).

The stove is a Dutchwest "Federal Airtight". The new liner is clean.

If any of ya'll got any DanG ideas, I'd sure appreciate them ;D

[doctorb]

Most wood stove manufacturers rec. an 8" pipe off the back of the stove.  I think it will change little as to how your stove works.

[tyb525]

The pipe from the stove to the wall is 8", always has been.

My thoughts are that the new liner restricts the flow, especially since the chimney is two stories, and because the liner is now corrugated, and not necessarily a straight shot all the way up (it might have a few slight curves in it because it is significantly smaller in diameter than the old clay liner). This all would reduce draft I would think.

[beenthere]

Sounds like trying to burn wet wood.

What is the history of the wood? when cut, how long since split, species, etc. ??

[Bill]

+1

imho - having to open up the air intakes is a sign there's more restriction in the " new " chimney ( liner ) . I'm thinking the new liner doesn't " flow " as well so needs a little more air to keep things going.  As long as the wood is still the same load of nice dry stuff . . .

I'd also think it allows somewhat " cooler air " to separate the new metal liner from the original clay liner ( maybe just the corners but still ) . I think that lowers the temperature ( even just a little ) which I suppose could also " lower " the drawing power of the " new " chimney.

at least that's my $0.02 and worth every penny of it   ;D

[mad murdock]

I think the only way to know for sure would be to have WC readings before and after the liner replacement to know for sure if it has made a difference.  Obviously something has changed since the stove is the same before and after the chimney repair, and the only thing different is the liner.  If you have a good HVAC tech that you could pick his brain, maybe that would reveal more light on the subject?  You can google Water Column meter, and maybe figure a way to make a simple one using clear pvc flexible hose? It is pretty easy to rig up something that will give you a fairly accurate read on actual draft conditions.

[tyb525]

The wood is the same as we've always burned, mixed hardwoods dried at least a year.

[Reddog]

Sounds like you need to talk to some new chimney sweeps.
I would question their install job.

[SwampDonkey]

Tyb, I am also wondering about that install job to. Can you see up the flu with a mirror? My uncle did some work on a kitchen flu that is on the outside of the house. Somehow a piece of metal, whether from the inside of the old flu liner or otherwise got lodged and the draft was restricted and would smoke terrible. When the draft on your stove is wide open do you get a rapid chug chug sound when the fire is flaming good? That is the sign of a good draft to me. The trouble with the outside flu is it's a lot colder than running up through the centre of the house. Of course you guys down there aren't in extreme cold like us northerners. But I've seen them outside flues with steel liners clog up near the exit, have a chunk fall down and cut off the air and turn the house into a smoke house. My uncle had that happen with a wood furnace hooked up to one.  A closed damped fire is a recipe for build up in the flu. Gotta get some heat up there. I leave my damper control on 80 degrees (thermostat controlled) to the furnace. That's half open. Of course it opens further when calling for more heat in the living space until the fire is gone out. This fall has been a mild one here, the fire has been left to go out many times. Otherwise too hot. :D

Time to throw a stick in.

[CX3]

Just another thought here, sometimes the direction of the wind can make a big difference in the draft.  I know if we have an E/NE wind our stove does not draft well because of some large trees next to the chimney.  Its almost like the wind comes around those trees and "down" the chimney.  When the wind switches the draft is great.  Also cool damp mornings can have a big effect on the draft.  It doesnt sound like this is your case, but thought I would say what our stove does. 

[SwampDonkey]

Yes, cold dry air draws better, more oxygen. But, don't think this is the issue here.

I would burn one of those chimney sweep logs every other month as well. They burn for 1-1/2 hours, just toss it in on low coals not on flames.

[mad murdock]

That is a good tip SD.  Those chimney sweep logs do work pretty well to cut down on build up.  I too would question the liner install.  It doesn't make sense that you would have that much of a change in such a short time. My previous suggeston on measuring W/C was to find out what was really going on, if everything else "looks" ok.

[tyb525]

We have a damper, but since the install there has never been a time to use it. Used to be on any kind of windy day we would have to close it some to keep the fire under control. We haven't touched it this year.

SD, I know the sound you are talking about, but I don't think I have noticed that sound recently.

[dsgsr]

If the chimney is on the outside of the house, it should be insulated. I just went through that prob.  I built an enclosure around the chimney 3/4 of the way up, would have gone a little further but had the roof pitch to contend with. First I built the framing with a 2.5" offset, (code) put 6" of fire/water proof insulation in and closed it in with plywood and covered with vinyl (same as house). It's working good so far. The metal chimney that was put in, should have been rapped with fire proof blanket. That may be your prob.

David

[Dana]

I had a similar problem a few years ago. I had a chimney fire and installed the flexible stainless liner to be safe. My bigest problem was that the liner cooled the smoke down so bad that I had watery creosote dripping from the stove pipe in the house.

I was going to pour a light weight concrete around the pipe to hopefully insulate it better. I had experimented with a vermiculate portland mix that I think would have worked. I bought an outdoor woodburner before I completed the experiment.

The liner I used was dura vent and as I remember they required an insulating wrap for the outside of the pipe. Did they install one?

[WH_Conley]

Another vote to question the install. If you know the name of the product you should be able to find installation instructions, to check if it was done right. I agree about the sound, it will tell if it is working right.

Has no bearing on your problem, but, I also had a flue fire last winter, cracked the masonry block flue and liner. Tore it out the next day and installed stainless steel insulated flue system. The old masonry flue drew pretty good. The stove is in the basement, had to have 2 elbows to hook it up. The new one is straight up, one elbow out the back of the stove. Have to leave the damper turned off or it sounds like a jet engine. Had creosote problems with the old system, not the new. If you have to do any more work on the flue you have you might check prices on the stainless. If you put it inside like SwampDonkey was talking about they are easy to hide. You also get some radiated heat from the pipe to.

[tyb525]

Correction, it's only 6" coming from the stove which is correct for that stove, but then the liner is also 6". The old liner was 12". I would imagine that the liner doesn't make a straight shot up the chimney - I picture it looking like a snake.

Also, no insulation was installed, but neither my mom nor I can remember the brand.

The chimney goes down to the basement, where a coal furnace used to be. The chimney installers left a T where the stove connects to the chimney, the bottom on the T is open. Could that be a factor also?

[SwampDonkey]

Take a picture Tyb so we can see it. The connection from the stove to the flu. Is the T inside the old flu? That's so you can hook up another appliance on the other side and the bottom is open to clean the flu. Also, what about your cleanout at the bottom of the flu? Take a piece of tinfoil and hold it up to the cleanout area (when the hole is closed off) and see if the tinfoil gets sucked to the chimney wall. All mine is at the bottom is two bricks I take out to clean the soot. Some are metal plates that cover the hole.

[CX3]

The bottom of the T being open would absolutely be a problem.  The draft is going to draw air from the easiest place.  In this case it is easier to draw air from an open pipe (the T) than it would be to pull air from a firebox full of wood.  Close that off. 

Also going from 12 inch down to 6 would also explain some of your problems.  That stove is not breathing like it was before.  You put a noose on its neck.

[SwampDonkey]

Yes if it's out in the room, a problem in deed. Then I have to ask why an elbow wasn't used? I can't picture that setup, the only "T" I use is the connect a flu from the oil furnace to that of the wood furnace. An oil furnace makes almost no smoke in an efficient burner. Best set up is an incline/slope from the stove toward that flu thimble, elbow at the thimble. Want as few turns as possible and then vertical up the flu. Furnaces here recommend at least 7" pipe, but you have to go with what the stove fitting it. Yours is 6" I guess. The 12 down to a 6" I can't see as a problem because you only have volume of 6" in the stove pipe, so it could be a cannon sized flu, it's only going to draw in from a 6" stove pipe.

[WH_Conley]

Pictures please. As CX3 said if that is open the stove doesn't have a chance. I am thinking that the "T" should be sideways, one straight leg hooked to the liner, the other straight leg plugged with a cap for the clean out, and the angle leg going to the stove.

[SwampDonkey]

Sounds like those boys were scrounging to make due if they went and done that. Something I'm not picturing. I have seen a T setup on a pipe in a shop stove, but outside the shop. And the bottom kept closed until cleaned.

[John Mc]

If I'm picturing your "T" correctly, it's a sideways T. What would be the top of the T is running vertically, hooked to your flue on one end, and nothing on the other end (which is pointed straight down) The stem of the T is pointing sideways, and hooks in to your stove.

The end which is not connected to anything should certainly be capped off. Your installer screwed up big time if he did not close this off. There are a couple of reasons for using a T rather than an elbow:

• You can remove the cap for cleaning, and brush out your chimney from below, rather than up on the roof (assuming it's high enough off the ground to get the rods in)
• The stub end of the T makes a place for any crud/cinders/creosote to drop into, rather than collecting in the elbow or the top of the stove.
• If sweeping the chimney from above, you can open the cap on the stub end, tape a trash bag around it, and anything swept out will fall straight down into the bag... you don't have to disconnect the stove

Unlike others here, I don't think the switch from 12" flue to a 6" would cause a problem with a stove designed for a 6" flue (as yours seems to be, judging from its 6" exit. In fact, an oversize flue can cause problems with draw and with creosote formation, since it will run cooler.

Like others, I do question the installation. If they just snaked a bare 6" liner down a 12" flue without and form of insulation, or something to take up the airspace, that liner is going to run cold -- especially if they did not seal off the extra opening at the top between the liner and the original 12" flue.

One other thing to check: is it possible the fire damage any part of your stove, or that crud from the fire dropped down the flue and is partially blocking the exhaust at the top of your stove? My stove exits straight up into the chimney (built to look like a fireplace, with a stove sitting in it). One year I did have some problems with stuff flaking off my flue, falling down into the stove and partially blocking the exhaust. I had to crank the air open to get it to burn at all, and it was still a pain in the neck. Disconnecting the stove and vacuuming out the opening made a big difference. (I would think a competent installer would have checked for debris in the top of the stove after a chimney fire, if the flue connection was such that it could have made it back into the stove.)

[SwampDonkey]

I have a clean out hole in my flu to brush out the flu. I don't try to clean a flu from a stove pipe. I remove my pipes monthly to clean them with a brush. It would take some snaking to get a flu brush around all them turns. My way the brush goes straight up from the bottom. Also, make sure your not using a steel brush in that new metal liner.

[tyb525]

The "T" is vertical - it is inside the chimney.

The bottom the T is open. The chimney men said that was to allow creosote to fall to the bottom, where there is a metal cleanout door.

The flu connection from the stove to the chimney is all original, it's been there since the stove was installed in the late 80's, however we take it apart and clean it every year. We also clean inside the stove. We clean the chimney with a brush-and-rope system: brush with rope on both ends, person at top, person at bottom. Pull all the way up, then all the way down multiple times. However, we haven't cleaned the new liner yet, we had the same guys clean it when we noticed that it wasn't performing the same.

It would make sense that smaller flu would increase the draft, especially if it is what the stove is designed for. However, considering the chimney is 2 stories, it seems like that would be too small a pipe for the volume of smoke. The old 12" worked much better.