Flue Improvements needed? Draft weak when not burn hot.

[bogydave]

Had Draft issues last night. Had to burn hotter but outside was warm 26°f &
Low pressure moved in. (opened windows to stay below 78 inside)
Called local Stove store guru.
Wanted pictures, so I sent them. Any pro or con to what he said appreciated.
Copied his response:

"Your stove is a newer vintage so it should be in good condition.
Your inside components should be all double wall black pipe an no single wall. The single wall allows for way too much air leakage affecting draft.
By going with 2-45 degree and less of a horizontal run would be best. Allow for a 1/2' rise for every 12" of horizontal run. Your choking your draft the way it is currently set up.

Your stove can be as close as 6" with the new double wall black pipe so this should help.

Your horizontal run through the wall is way too long.

Your TEE should be on a wall support kit and mounted 2" from the house with the pipe going through the eve.

There are way too many chimney components. Looks like a kaleidoscope of mixed pipe. Some may have gone through a chimney fire from the looks of it. I recommend that you use the longer 4 foot insulated pipe sections. This eliminated all the chimney sections that allow for air to come into the flue causing tremendous loss of draft.

Follow these recommendations and you will find out that your stove works just fine on a very low setting.

Adding a bit of height by at least 2' to this stock column and securing with a roof brace kit for wind support."

Not planning on moving the outside stack closer to house, (vinyl siding) but other recommendations sound good. Will have to buy pipe from him, not allot of choices. But that's OK. nice to have a source in our area.

 

[begreen]

He's right. You'll want to keep the exhaust warmer. Switching to double-wall and a pair of 45's instead of the 90 is a good suggestion. Put the exit 45 right at the thimble.

 

[North of 60]

+1 on all his advise Bogy. Looks like he addressed it fair and honest. Looks like he took some time to do it too. Now lets hope for his sake that it wasnt his outfit that installed it. :lol:
Good luck on your upgrades this summer.
Cheers

 

[bogydave]

He's right. You'll want to keep the exhaust warmer. Switching to double-wall and a pair of 45's instead of the 90 is a good suggestion. Put the exit 45 right at the thimble.

By "thimble" do you mean the metalbestos going thru the wall?

 

[bogydave]

+1 on all his advise Bogy. Looks like he addressed it fair and honest. Looks like he took some time to do it too. Now lets hope for his sake that it wasnt his outfit that installed it. :lol:
Good luck on your upgrades this summer.
Cheers

The "outfit" that installed it is typing this response :-/

 

[North of 60]

P.S. The vinyl siding should not be an issue. I personally would build an insulated chase due to your climate.

 

[North of 60]

+1 on all his advise Bogy. Looks like he addressed it fair and honest. Looks like he took some time to do it too. Now lets hope for his sake that it wasnt his outfit that installed it. :lol:
Good luck on your upgrades this summer.
Cheers

The "outfit" that installed it is typing this response :-/

Well then.......YOU GOT HIM BY HIS LEFT TESTICLE.

 

[begreen]

He's right. You'll want to keep the exhaust warmer. Switching to double-wall and a pair of 45's instead of the 90 is a good suggestion. Put the exit 45 right at the thimble.

By "thimble" do you mean the metalbestos going thru the wall?

Yes.

 

[bogydave]

P.S. The vinyl siding should not be an issue. I personally would build an insulated chase due to your climate.

Good idea. Would look much nicer too.
Added to the "to do list".
That one is a few day'r, with some siding work thrown in.
Won't tell my wife that one, she complained about "that ugly chimney" already (but likes the
heat in the house above 65. At 74 the complaints went away )

Thanks
*******
Thanks BeGreen,
may see about it tomorrow. If I can get the pipe, should be a quick fix.
Just money

 

[nate379]

I am having same exact trouble with my draft as well as a few of my friends. I don't remember where you live exactly, but I think it's somewhere near Palmer?

I think it's the weather/baro pressure more than anything. After fighting with getting a fire going good today for over an hour I decided I'm done with it and just going to use the boiler. It's too much of a headache to fight with the weak draft and try to make a small enough fire so it's not 85* in the house.

Your setup looks ok to me. I don't know why they didn't use 4ft lengths, but that isn't the end of the world. Could try to put another length on the chimney, but I doubt it will be enough to help... other than get torn off in teh wind.

 

[Todd]

I think before I would spend all that money on new double wall pipe I'd try moving the stove a little closer to shorten up that horizontal pipe run and give it a little more rise towards the thimble. I'm a big fan of the extra heat you get from single wall if you can maintain good draft.

 

[Backwoods Savage]

Had Draft issues last night. Had to burn hotter but outside was warm 26°f &
Low pressure moved in. (opened windows to stay below 78 inside)
Called local Stove store guru.
Wanted pictures, so I sent them. Any pro or con to what he said appreciated.
Copied his response:

"Your stove is a newer vintage so it should be in good condition.
Your inside components should be all double wall black pipe an no single wall. The single wall allows for way too much air leakage affecting draft.
By going with 2-45 degree and less of a horizontal run would be best. Allow for a 1/2' rise for every 12" of horizontal run. Your choking your draft the way it is currently set up.

Air leakage in single wall pipe? Heat leakage I agree but not air leakage.

I do like his advise of 1/2" rise per foot of horizontal. 1/4" is usually quoted but 1/2" is better. I speak from experience on this one. You could even go more but then you would have some problems connecting things.



Your stove can be as close as 6" with the new double wall black pipe so this should help. I agree.

Your horizontal run through the wall is way too long. Maybe so, maybe not.



Your TEE should be on a wall support kit and mounted 2" from the house with the pipe going through the eve.

This is a matter of who does the installation. For sure, closer would shorten the horizontal but I've seen some longer than yours and no big problems. So if you shorten the horizontal, you do some cutting up above. Do you want to do that?

There are way too many chimney components. Looks like a kaleidoscope of mixed pipe. Some may have gone through a chimney fire from the looks of it. I recommend that you use the longer 4 foot insulated pipe sections. This eliminated all the chimney sections that allow for air to come into the flue causing tremendous loss of draft.

How much air can leak into the chimney?


Follow these recommendations and you will find out that your stove works just fine on a very low setting.

Adding a bit of height by at least 2' to this stock column and securing with a roof brace kit for wind support."

Height is good but it is also amazing sometimes how easily you can get away from it. Mine is a lot shorter! No problem.

Not planning on moving the outside stack closer to house, (vinyl siding) but other recommendations sound good. Will have to buy pipe from him, not allot of choices. But that's OK. nice to have a source in our area.

Of course building a chase might be good in your area, however, you have not mentioned a problem until the temperature got up to 26 degrees! So cold air causes no problem? A chase has been recommended to me by lots of folks; some who have seen our chimney but most who have not seen it. I will admit that the first time I ever used a chimney like this I figured I'd have to build a chase but have never needed it so have saved the dollars.

Good luck Dave.

 

[Battenkiller]

Your setup looks ok to me. I don't know why they didn't use 4ft lengths, but that isn't the end of the world. Could try to put another length on the chimney, but I doubt it will be enough to help... other than get torn off in the wind.

I agree. You can certainly try monkeying with it, but I'm more a believer in system planning by the book rather than through experimentation.

If you look at any standard draft table from the hearth industry, you'll see that adding height has a minimal effect on static draft unless you add a lot of it (as in several feet). This is especially true at lower flue temps like are found in cat stoves. The height effect on draft is much more pronounced at the higher flue temps that might be typical of older airtights. Often neglected in these discussions is the increase in total system resistance caused by adding extra pipe. Not much for only 2 feet (about a 0.10 resistance coefficient), but fully equal to the small gain gotten by use two 45s instead of one 90.

The horizontal run shouldn't significantly affect draft, either. Only the resistance of the pipe itself to flow is a factor, and again, you can look at a draft table to get the difference in resistance. Looking at system resistance coefficients alone, you can see that 8" pipe has a coefficient of about 0.05 per linear foot. Your stove alone,with it's damper closed, probably has a resistance coefficient of between 15 and 20 (maybe a lot higher when it's stuffed to the gills with wood). I don't thing that silly extra foot of horizontal pipe is making much of a difference at all (maybe 1/4 of a percent). Like Todd, I'm also a big fan of the heat recovery gotten from single wall pipe. 1 foot of 8" pipe at a 250ºF surface temp radiates about 1000 BTU/hr. Not huge, but why lose it if you don't have to?

As I mentioned above, switching to two 45s rather than one 90 will have very little effect on total system resistance... about a 0.10 lower resistance coefficient. Again, very little gain for a whole system whose total resistance coefficient might be between 20 and 25.

Anyway, before you make all these expensive mods, I'd suggest you invest $30 in a manometer to actually check the strength of your draft during the troubling conditions instead of just assuming the draft in insufficient. It may be stronger than you think. If not, I think the very best advice given to you was to try to eliminate air intrusion into the flue. Try pulling the single wall section apart and sealing the seams and connections with stove cement. A lot more air gets in there that we'd all like to believe, and that had a measurable effect on flue temps. Flues temps have a greater effect on draft than any of the other factors.

 

[Battenkiller]

Of course building a chase might be good in your area, however, you have not mentioned a problem until the temperature got up to 26 degrees! So cold air causes no problem? A chase has been recommended to me by lots of folks; some who have seen our chimney but most who have not seen it. I will admit that the first time I ever used a chimney like this I figured I'd have to build a chase but have never needed it so have saved the dollars.

Excellent point, Sav. We all know how well your "sub-standard" chimney works for you and your stove. ;-)

I personally feel the chimney height thing is over-rated. If stoves only worked within very narrow draft conditions, most of us would be constantly either struggling to get the stove to burn or else over-firing the thing all the time. Chimneys should be designed for the conditions under which the appliance will be run 95% of the time. We all suffer from less than ideal burns the other 5% of the time, it just goes with burning wood. Subtle adjustments in wood type, split size, load size, load timing, fuel MC, air control, etc. can defeat most of this stuff once you get used to how your stove works over time. That's why, in the end, it's really an art.

 

[nate379]

I just think it's not co-incidence that we live in same area, very different chimney setups that both burned well all winter but now have the same exact problem.

All the info I have read suggested min chimney length of 14-15ft for a good draft. Not draft that will be "eh".

If you look at this chart, just adding a few feet doesn't seem like it'd do much at all.
http://docs.engineeringtoolbox.com/documents/175/chimney_draft.pdf


At my folks, they have a stove in the house and one in my Dad's shop. Both brick and liner, 6" flue. The shop is right next to the house.

Setup in the house has never had a great draft. In the shop even in the middle of summer, it will darn near suck the match out of your hand. Toss paper in the stove and light it and it will shoot burning paper outside. It was bad enough my Dad had to put 2 dampers in the stove pipe. Both chimneys are about 20ft in length. Why such the difference? The ONLY major difference is the shop chimney is 20ft from ground while house is 20ft from basement, so about 12ft from ground.

 

[Battenkiller]

If you look at this chart, just adding a few feet doesn't seem like it'd do much at all.
http://docs.engineeringtoolbox.com/documents/175/chimney_draft.pdf

Nate, the scale of those charts is way beyond the range of static drafts typically found in a wood burning home chimney. There is a bigger effect than those graphs can resolve at the low end. They are more appropriate to smokestacks than to stove chimneys. 0.5" of draft in a stove would cause an overfire in a heartbeat. 0.05" is more like it.

Here is a useful chart taken from "The Woodburner's Encyclopedia", by Dr. Jay Shelton:

 

[nate379]

That chart doesn't make any sense to me. A 30* difference in outside temp... where does that show on the chart?

I have no idea what temp the smoke is.

 

[billb3]

Did you have the draft issues before or after you opened the windows ?

Basement stoves can be finnicky about air supplies.
Even kneewall basements.

 

[bogydave]

Did you have the draft issues before or after you opened the windows ?

Basement stoves can be finnicky about air supplies.
Even kneewall basements.

Draft is good with or with out window open (no change open or closed).
I tightened my house up allot, but even after the upgrades from the energy audit, his "how much the house leaks air" measurement "After"
was above what is needed t operate a woodstove.
I only open window to cool the inside house temperature to
a livable temp. At 77° I find it almost unbearable This is Alaska, we don't get those temps on a hot summer day.
I never get acclimated to much above 75°.
Even the mosquitoes hide on sunny summer days above 70 :lol:

 

[Backwoods Savage]

I keep thinking about the mountains. I know they are not real close but I do have to wonder if the might affect the drafting. Am I off the wall here?

 

[bogydave]

I keep thinking about the mountains. I know they are not real close but I do have to wonder if the might affect the drafting. Am I off the wall here?

About 5 miles.
I have no idea. Tough to move them though :lol:
190 miles to Denali

 

[Backwoods Savage]

But they can be moved Dave. It just takes time.

I just keep thinking how the mountains affect air flow and temperature inversions, etc. and it just seems to me they could very easily have some effect on your drafting.

 

[woodchip]

Now the shoulder season is here I have noticed a poor draughing a couple of times when the fire has gone quite low, and it was a window that had been left open in the lee of the wind causing a slight vacuum indoors.

Never happened when it was really cold (well, few people round here leave windows open in freezing weather).

 

[leeave96]

I think you got a pretty good set-up in general. The chimney looks plenty tall.

A double wall stove pipe will help with draft, but single wall should be OK - and I think that your stove has an 8 inch stove pipe? If so, a double wall 8 inch stove pipe might look pretty bulky.

My advice would be to move the stove closer to the wall - to the minimum allowed and build a chase around your chimney for additional insulation.

Good luck,
Bill

 

[bogydave]

Did basically what you recommended
Pic in new thread:
https://www.hearth.com/econtent/index.php/forums/viewthread/73529/