Author Topic: Idea to make wood burning stove more efficient  (Read 15354 times)

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Jrmobb

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Idea to make wood burning stove more efficient
« on: November 26, 2007, 06:40:16 PM »
I hope this was talked about before but i could not find anything in the search.


Has anyone ever tired diff ways to make a wood burning stove more efficient by extending the chimney in the house for more radiant heat and added a angled piece of metal to project the heat? also add  disks to the chimney for even more radiant heat?


would the angled metal get to hot after a while?


« Last Edit: November 26, 2007, 06:40:16 PM by (unknown) »

Jrmobb

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Re: Idea to make wood burning stove more efficient
« Reply #1 on: November 26, 2007, 11:42:40 AM »
sorry for typo's, I just let spellcheck do its thing and it messed it all up
« Last Edit: November 26, 2007, 11:42:40 AM by jrmobb »

A6D9

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Re: Idea to make wood burning stove more efficient
« Reply #2 on: November 26, 2007, 11:51:02 AM »
I"m not an expert so take my advice liek a grain of salt.


But if you put your chimney allmost horizontal liek that, it will lack a good draft I would assume.  and we all know a draft is very important to have fire in a house.


if you look at a chimney some are not air tight sealed.  but still never elak smoke in the house.  this is because of the draft that sucks everything out the top of the chimney.  


If you wanted to go horizontalk like that, I would suggest a really tall chimney outside to capture mor wind to creat more draft.

« Last Edit: November 26, 2007, 11:51:02 AM by A6D9 »

Nil

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Re: Idea to make wood burning stove more efficient
« Reply #3 on: November 26, 2007, 12:28:16 PM »
I don't believe it would be a great idea. I'm sure it would work but would cause more problems than it is worth. One of the things to consider is taking heat away from the flue gases will cause more creosote to build up and cause a bigger fire hazard, the flue gases work roughly the same way steam does; the water is in vapor form until it cools enough to drop out of suspension. With a horizontal pipe and 2 90 degree bends in there it'll be a bear to clean out.


It'd probably be a better idea to try and get as much heat out of the burning wood before it leaves the fire box, just make sure you don't cool the gases too much or the creosote will be more apt to drop out of the flue gas before it travels out of your chimney.


If you have the resources go for it. I'm up for it if it works, just don't have the ability to try myself.


Maybe someone else has another take on the idea?

« Last Edit: November 26, 2007, 12:28:16 PM by Nil »

TomW

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Re: Idea to make wood burning stove more efficient
« Reply #4 on: November 26, 2007, 01:05:16 PM »
Well, lets see, here;


Poor, cooled exhaust draft for smoky house.


Excess creosote buildup for an even smokier house as the house burns.


Chimney pipe sags then collapses from heat and gunk build up in the pipe. More smoke from a burning house.


Just plainly a bad idea. Even if it works safely you wont save much firewood. Just cut another load of wood, it is much safer.


I know of this type long horizontal run stove pipe and have seen the house damage from smoke and fire. Especially if using that steel pipe they sell in most hardware stores.


Flue pipes should run vertically with very little horizontal run. I stopped using that cheap steel pipe too. It needed replacement every other year tops. I now use stainless steel flue from stove to chimney. It cost an arm and a leg but has been in use for about 7 years and I expect it to outlast me.


Bottom line with wood heat is do not cut corners. You will regret it. I tend to burn smaller loads of wood hotter and this seems to boost efficiency over a big fill and cramping off the air to control the heat.


Just sensible advice from a guy who has heated with wood his entire life.


Cheers.


TomW

« Last Edit: November 26, 2007, 01:05:16 PM by TomW »

wooferhound

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Re: Idea to make wood burning stove more efficient
« Reply #5 on: November 26, 2007, 01:47:54 PM »
It seems as if some heat sinks on the exhaust pipe near the stove would work better though. I hear that the flue gasses need to be at 500 degrees or more or they start to condense on the pipe walls.
« Last Edit: November 26, 2007, 01:47:54 PM by wooferhound »

feral air

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Re: Idea to make wood burning stove more efficient
« Reply #6 on: November 26, 2007, 02:23:47 PM »
Interesting, I burn the opposite way; cram the box and let it simmer. I'm not concerned about efficiency, I just like the even temp that gives. Besides that I only have to open the box twice a day, in the morning and again before bed.


Are there any major drawbacks (or hazards?) to the way I've been doing it? I clean the chimney pipe every year since it has a slight bend in it (required to get around a stud) so if the only drawback is extra buildup I'm not too concerned.


One of the ideas I've been kicking around in my head the last few days (based on a previous thread) is to use a stove-top fan to pull cold air from the outer rooms over to the wood stove. We have several rooms that tend to have their doors closed so they're a lot colder than the common areas of the house. Since we already have duct work under the house and vents throughout (for the electric furnace that's never used) I figured I might be able to use 'em. I'd close the ducts in the common areas, except for the one near the wood stove, and then hook that vent to the fan atop the stove so that it pulls the cold air in.


Do you think something like that has a chance of working? take it easy

« Last Edit: November 26, 2007, 02:23:47 PM by feral air »

jmk

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Re: Idea to make wood burning stove more efficient
« Reply #7 on: November 26, 2007, 02:28:00 PM »
 My dad put a Franklin stove on the floor in front of the hearth. It had a single pipe elbowed straight off the stove. It ran about nine foot to the next elbow to get it up a two story brick fireplace. We saw the pipe get red hot all the time. The stove feed lots of oxygen to the wood so it burned fast and hot. The pipe probably heated just as much as the stove. It wasn't a great Idea though. If you want to save heat I would try getting outside air piped to the intake of the stove. All these stoves and fireplaces that suck up inside air are just pulling in outside air from the windows and doors. If you have an air tight house then a window has to get cracked to get the draft to work or it will smoke. When looking at the smoke coming out of the top of the flue the rate that it comes out is the same rate that cold air is entering the house to feed that draft. Feeding outside air directly to the stove creates a positive atmosphere in the house and will help to get rid of the cold window drafts. Just remember that what goes out the flue also is coming in as cold so it's hard to be efficient. That's another nice thing about an outdoor stove. I have an insert in that same fireplace now that came with fittings for outside air on booth sides of the front of the box. I spent $1,200 on it. used it for two years then baught an outdoor boiler. I put birch logs in the house and don't ever light it.
« Last Edit: November 26, 2007, 02:28:00 PM by jmk »

TomW

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Re: Idea to make wood burning stove more efficient
« Reply #8 on: November 26, 2007, 04:03:21 PM »
Woof;


I figure a fan just blowing across the firebox would boost thermal extraction with little or no safety issues. The fan would take energy, tho.


Cheers.


TomW

« Last Edit: November 26, 2007, 04:03:21 PM by TomW »

RogerAS

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Re: Idea to make wood burning stove more efficient
« Reply #9 on: November 26, 2007, 04:43:12 PM »
Hey,


I heat with wood, hardwood to be specific, and I would NOT run a pipe like that. Others have said no and I do as well. Good way to get dead.


You might be interested in this, my solution to wood heat:

http://www.fieldlines.com/story/2006/10/17/151918/06

and

http://www.fieldlines.com/story/2006/10/12/1352/1405


It keeps all the wood mess, smoke, most all danger and ashes outside. No energy used, aside from the fire, to convect air in my house. I'm seriously considering adding a heat exchanger to preheat water for the tank.


There is a functional sterling stovetop fan available for those that must have the stove inside, and a google search will find it. Runs off the heat of the stovetop.


Wood heat is carbon zero. You release no "old" carbon as in a fossil fuel. I love it. However I do consume some fossil fuels getting the wood. I have a good running chainsaw will use about 1/5 gallon of gas/oil per rick of wood(4 rick per cord), and a lesser volume of chain oil. So I use about 4 gallons of gas/oil and 1.5 gallon of bar/chain oil estimate I use about 4 cord per winter. I'm cleaning up a lot of dead wood and it burns fast. The trick is to cut hardwood green, let it age, and then burn it. Seasoning a log is a bad idea, unless one likes ruining chains on rock hard oak and hickory.:-)


I'm still recovering from an ice strom we had here 4 "Black Fridays" ago, to the day. It sounded like a war in my forest, hundereds of limbs and whole trees snapped for 24 hours. Scary! Anyway, seasoned like steel or not I've GOT to cut my dead hardwood.


RS

« Last Edit: November 26, 2007, 04:43:12 PM by RogerAS »

bob golding

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Re: Idea to make wood burning stove more efficient
« Reply #10 on: November 26, 2007, 05:33:28 PM »
having just spent the best part of the last 2 months ,on and off, fitting a wood stove in an old granite cottage i have learnt a few things. in the UK you are not allowed under the building codes to have more than a 45 degree bend anywhere on a wood stove flue. so thats out. you want to insulate the flue as best as possable to keep the heat IN the pipe. this stops the condensation forming on the pipe and rotting it out. if you try and extract heat from the pipe all you will do is reduce the draft and rot your pipe out quicker. the way to get more heat out is to fit a baffle in the top of the stove to direct the flames over the baffle and into the flue. this heats up the smoke and gives a longer flame. wood is a long flame fuel i have been told by a potter. of course this will only work if you have a front loading stove not a top loading one. i modified a coal burning stove like that 20 years ago and it still works fine, sitting next to as we speak in fact. the forced draft idea would work as well. bottom line get the heat in the stove and keep it hot going up the flue.


cheers

bob golding

« Last Edit: November 26, 2007, 05:33:28 PM by bob golding »
if i cant fix it i can fix it so it cant be fixed.

nick1234

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Re: Idea to make wood burning stove more efficient
« Reply #11 on: November 26, 2007, 05:44:52 PM »
buy your drawing it looks like a airtight stove. when i installed  my airtight stove

it said to avoid any bends as much as possible with the shortest run to the chimney

it work the best that way. now having said that  in may tool shed i have a old franklin

Leakey as hell i use as long as possible stove pipe. To get as much radiate heat as i can get out of it with a slight tilt up on the horizontal, have to clean it out once a year

 
« Last Edit: November 26, 2007, 05:44:52 PM by nick1234 »

spinningmagnets

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Re: Idea to make wood burning stove more efficient
« Reply #12 on: November 26, 2007, 06:17:23 PM »
I have never used wood heat, but I think it will play an important part in my retirement soon. One of the important parts of the German "Passive House" standard is a long heat exchanger that forces the air that comes into a well-sealed house to pass along side the warm air going out. Regardless of the heat source, this cuts the size of the heat system in half.


If drawing more heat from the flue is a bad idea (to prevent creosote and corrosive gasses) what would be the best heat exchanger to draw as much practical heat from the firebox as possible?


Is "forced draft" required for a system that draws so much heat from the fire that the flue may not flow well?


"Last week I stated that this woman was the ugliest person that I had ever seen. I have since been visited by her sister, and now wish to withdraw my previous statement" -Mark Twain

« Last Edit: November 26, 2007, 06:17:23 PM by spinningmagnets »

Drives

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Dry Wood
« Reply #13 on: November 26, 2007, 06:31:13 PM »
I have done the horizontal pipe years ago....first year had to clean the pipe out 3 times in one year.  Second year, had the "sag"  Tom spoke of until it opened a crack in the pipe, and had a nice roaring creosote fire in the pipe....not good.

My two bends are now 45 degrees, near vertical short pipe runs.


Another way to increase heat output is the proper seasoning of firewood  i.e. DRY.


I had a older friend of mine call me up and asked me to empty his old shed of dried 10 year old black locust firewood logs.  He warned me to be careful, said they could burn down my house because of how hot they would burn.  He was right!  It was amazing how little wood I would need to load into my wood stove to get an enormous amount of heat for a very long time.

I try to burn quality hardwood (oak, cherry, ash, hard maple, etc) that has dried under cover for at least 2+ years.  The difference between cut in the spring/burned in the winter, and 2+ year old, dry, wood is noticeable.  Plus, I don't have the creosote build up issues that green wood causes.


Just some thoughts.


 

« Last Edit: November 26, 2007, 06:31:13 PM by Drives »

SteveCH

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Re: Idea to make wood burning stove more efficient
« Reply #14 on: November 26, 2007, 08:03:20 PM »
The reasons why this is a bad idea have been covered, I'll just add that I agree, bad idea.


I've been heating with wood since 1974, 100% of my heating. I like it. I, too, initially tried to figure out ways to make use of that heat lost up the pipe.


If it makes you feel better, think of it as the heat you simply have to let go in order for the stove to work properly and safely. You can recover much of that stovepipe heat; however, as the other posters said, there is a price to be paid. Instead, pay the heat loss price, it is simply part of the "cost" of the physics and chemistry of operating the stove. Some stoves are more efficient than others; some stoves are a LOT more efficient. Get the best stove you can [which doesn't necessarily mean the most expensive] and you'll be in good shape.


I know a fellow who ran a pipe from outside to the air intake on his stove, which is an opening below the ash grate, machined into the side of the stove. He bolted the pipe, with fittings, to that opening and supplies the combustion air to the stove that way. I had thought of this myself, and there are stoves designed for this [or at least used to be back in the 70s, don't know if they still are being sold]. I never did alter my stove, but I built a fireplace and used the same sort of thing, two large pipes that open up in the ash dump beneath the grate, controlled by a metal door. Works fine, keeps the fireplace from pulling too much indoor air up the chimney.


Things like that will help you and be safe. It is the nature of the smoke, the elements in it, and the need for heat for efficient draft, that you just have to spend some heat to make it all work well.

« Last Edit: November 26, 2007, 08:03:20 PM by SteveCH »

hiker

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Re: Idea to make wood burning stove more efficient
« Reply #15 on: November 27, 2007, 08:22:59 PM »
add on a stack robber--its just a box with tubes inside--add a fan on the back side..
« Last Edit: November 27, 2007, 08:22:59 PM by hiker »
WILD in ALASKA

scorman

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Re: Idea to make wood burning stove more efficient
« Reply #16 on: November 28, 2007, 09:12:30 AM »
I am currently using a $200 converted 30 inch "heatalator" steel firebox as a wood furnace for a 2800sqft ranch style house in midstate NY.

http://www.yourwayfireplaces.com/docs/Air%20Circulating%20Metal%20Fireplaces.pdf

House is divided into baseboard hot water and forced hot air systems, both run from an oil boiler.


I burn 24inch split hardwood logs.

Unit is in the basement and surrounded by masonry walls and floor.


The masonry chimney had a clay thimble for a conventional wood stove installation.

Original glass fire doors were replaced with sheet metal inserts, since the tempered glass continually broke from the high box heat.

I have an external damper control to reduce flue volume


I have three means of extracting heat:


The flue has a double bank of horizontal 1 inch steel pipes to act similar to the sheet metal "stack robber" flue extractor commercially sold (but IMHO way to flimsey).

A small centrifugal blower pumps 1/2 the air through the tubes into the air return duct, the other 1/2 directly into the unfinished shop basement.

I don't have to worry about soot buildup ...turn off the fan and it glows red!


The heatalator internal double wall enclosure is ducted into the hot air system with 6 inch standard round ducting.

A flat plate water heat exchanger is mounted at the rear inside surface of the firebox.

It is plumbed into the recirculating line of the hot water baseboard system.


From the wood furnace, I have the means to turn on the flue extractor blower, the baseboard circulator pump , as well as one extra zone valve, as well as the air circulator blower,which has a thermostat control on furnace as well so as not to blow cold air.

There is a stack thermometer above the heat extractor which typically shows between 250 and 300 degrees F ...if I have too many small pieces which burn faster ..it gets up to 400degrees. The masonry stack is exposed brick in the living space on main floor and provides radient heat.


I currently burn three 3/4 loads per day ..will require four full loads for mid winter.

I consume 5 full cords of dry firewood per season and only use oil as backup.

The entire house can be kept between 65->70 degrees easily and all the floors are warm and provide radient heating as well.


I do not have photos of the installation, but if requested, I can post some.

RE also consists of passive sun room and current wind turbine project as posted in my profile


Stew Corman from sunny Endicott

« Last Edit: November 28, 2007, 09:12:30 AM by scorman »

DigitalMind

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Re: Idea to make wood burning stove more efficient
« Reply #17 on: November 28, 2007, 09:13:11 AM »
I know nothing about wood stoves, but read this article from the Mt. Best website and that's pretty much what they did.  (Not totally horizontal though, more of an upward angle but not straight up.


Just follow the link ! :)


http://www.mtbest.net/wood_stove.html

« Last Edit: November 28, 2007, 09:13:11 AM by DigitalMind »

TomW

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Re: Idea to make wood burning stove more efficient
« Reply #18 on: November 28, 2007, 02:12:36 PM »
DM;


Yeah, well, it sounds like they only fire that up rarely so drawing any parallel with real wood heating installs in a cold country is an apples to pecans comparison. That mtbest install is far from the flat horizontal run depicted in this original posting. Then the question arises "how is that supported"?


I could hunt the internet and post a few dozens of photos of crazy stove installations but that won't make them sane. I have trouble swallowing that 80% efficiency claim, too. Again it is apples to pecans type comparison unless he can show it somehow beyond saying it. Some rough math. Say a user burns 10 pickup loads a year. That 9% increase he claims will represent less than one load of wood. Maybe $100 here delivered  and stacked [could be more i do not buy wood]. Thats a lot of risk for $100. If you ever experience any type of venting failure on a wood burner you will respect the importance of a solid and proper install.


I just hope they never experience a chimney fire because that single wall pipe will collapse and spill burning debris on that what looks like wood floors and then its all over but arguing with the claims adjuster that your installation was proper.


Wood heat is perfectly safe but it can be quite dangerous. That setup qualifies as the later IMHO.


Just a pet peeve of mine, using "found this on the internet" to reinforce the appearance of sanity in a bad idea.


Not my problem but I think it is important to vocally oppose ideas that could get someone killed.


Carry on.


Cheers.


TomW


Cheers.


TomW

« Last Edit: November 28, 2007, 02:12:36 PM by TomW »

DigitalMind

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Re: Idea to make wood burning stove more efficient
« Reply #19 on: November 28, 2007, 02:18:36 PM »
I have no problems admitting that I don't know about something, which is also pretty much the first sentence in my post.  I just figured it would be worth posting the link though since it was directly related to the persons question.
« Last Edit: November 28, 2007, 02:18:36 PM by DigitalMind »

HenryVG

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Re: Idea to make wood burning stove more efficient
« Reply #20 on: November 29, 2007, 10:34:48 AM »
Let me weigh in with another vote to the "get another cord of wood and run the pipe vertical" group. My wife has heated with wood her entire 38 years and typically goes through about 8 cords/winter. She gets old "scared of heights Henry" up on the roof before the season, at the mid-winter thaw, and at the end of the season to brush the chimney out. So with a clean pipe, not too starved fire, and a $10 box fan on a shelf 5 feet to the side, we have a safe system that passes her insurance company's inspection.


We probably would get more efficiency by venting in outside combustion air, but there's no easy and cosmetically pleasing way to do this. If we did, we could probably even run the furnace fan to circulate the air without causing the smoking that this causes with an unvented stove.


Even if you're buying it, wood is cheap compared to running out of your house in the winter with whatever you could grab on the way out. Safety first! And put a fire extinguisher near the stove! I bought one two years ago (the first one she's ever owned) and you can always use it on the boat to pass inspections in the summer ;^}


Henry

« Last Edit: November 29, 2007, 10:34:48 AM by HenryVG »

shay

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I've been dealing with this for decades :-)
« Reply #21 on: November 30, 2007, 12:58:40 PM »
and there is always something new to learn. There are also REGULATIONS that interfere with efficiency because of safety.


First, the maintenance of the stack

Second, the quality of the heater

Third, the quality of the wood

Fourth, the methods of heat extraction

Fifth, the operator

Sixth?


I noticed there was an Alaskan commenting on the stack robber (Magickheat, Heatolater, etc). Having burned wood that was soaked in seawater in SEAlaska and had a roaring stack fire on the third story of a mountainside home in Ketchikan (with a stack robber) in the middle of an ice storm. I could comment on that!


So, I asked around when I lived on Orcas Island in Washington, about the stack robber with an airtight stove and they said no problem! This time on a 2 story house with a humongous stack fire in a double sheet-rocked plennum surrounding the stack!


So here is my answer:


!. Shortest verticle stack possible with ease of cleaning the priority!



  1. Twice a year during the burning season I clean the stack (or more often if I've smudged the fire).
  2. I burn superdried wood only.


By now you probably wonder "What happened to the heat efficiency we were asking about?".......I'm getting to that!


My current heater is an Irish Ashling from Waterford. I asked an expert about using a stack robber with this stove: "If there ever was a creosote generator it would be an Ashling with a stack robber!" was the reply and it is against the law to do that in Washington State!


So, just last month after two years of the Ashling's operation and the Magickheat sitting in the garage I put the Magickheat in line for a trial. We had been sending, maybe 1/3 to 1/2 of the heat up the stack! The Magicheat runs 100% of the time if the heater is properly managed and there is no discernable accumulation of soot/creosote on the stackrobber scraper. The Ashling has the auxiliary squirrelcage fan to blow air over all that cast Iron. It ran half the time over the previous two years and still does.  


In Yosemite National Park I saw my first horozontal run of stack...amazing...it ran the length of the building just over our heads and it was doing a toasty job. I don't know how often they cleaned it (it was sure to be a nasty job) and I don't think they ever stopped the fire during the winter. Maybe the place burned down....


Now-a-days it goes like this. If you want to play the insurance game, and don't know what you are doing with a wood heater, follow the regulations. If you have some knowledge of woodburners, operate your stove for high efficiency, and train others to do it properly when you are away it should be ok. They might not/probably won't or some stage in between, so CLEAN THAT STACK more often than necessary for their sake. And yes, I've been known to "smudge my heater" to extend the burn. It's all a compromise.


You should be impressed witnessing a stack fire. I haven't seen what one would do to triple wall stainless but I won't ever witness another stackfire in my home! Single thickness pipe radiates alot of heat and may be illegal, so there goes more heat up the chimney with double or triple wall.  


Finally, smaller stoves concentrate the heat so that stack and even the stove can get cherry red.....enjoy!


   

« Last Edit: November 30, 2007, 12:58:40 PM by shay »

scorman

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« Reply #22 on: December 03, 2007, 09:09:08 AM »
Just uploaded a bunch of photos of my installation ( no particular order):

http://s145.photobucket.com/albums/r203/scorman1/fireplace/


that hunk of melted 1/4" glass is what was left in coals after the tempered firedoor disintegrated ...switched to steel plates after the third glass shattered


BTW, NEVER had to clean out the two story clay masonry chimney ...never had a chimney fire in 15 years ...once in a while, I'll put in a bunch of smaller logs and let the stack gage hit about 500 degrees, turn off the stack exchanger fan for a minute and let it glow red (1" schedule 80 pipes) ...burns any residual accumulation


I burn only well dried hardwood and inspect the flue liner from the roof every season ...can scratch off some flaky soot with my fingernail and see the clay ...after startup, chimney smoke is clear for several hours ...


Stew Corman from sunny Endicott

« Last Edit: December 03, 2007, 09:09:08 AM by scorman »