Chimney preheating-how many do it and how?

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Badfish740

Minister of Fire
Oct 3, 2007
1,539
The consensus on my chimney design seems to be that it's not ideal (outside chimney, furnace is located in the basement), but it's all I have for the moment because I definitely don't have the $$$ to enclose it-maybe next year. So now my thoughts have turned to ensuring that I start with a good draft. I definitely won't be burning 24/7 this winter because my wife is barely comfortable with the idea of having a wood burning appliance in the house right now, so it will take a while for her to get used to the idea of tending the stove when I'm not home. She works fewer hours than I do and commutes only a few miles so she gets home four hours before I do, so ideally one day she'll get the stove going again when she gets home, but for now I'll be tending the fire on my own-oftentimes starting with a cold firebox. I did a little searching and found various techniques for chimney preheating and draft induction via everything from leaf blowers to hair dryers to propane torches. I have a small electric leaf blower that would probably fit perfectly into the outlet of my firebox, but I'm wondering if using heat, rather than a high velocity stream of air, is more effective, so I also looked at the torch method. Using heat sounds good, but the flame seems relatively small compared to the volume of the chimney. I looked into larger torches-McMaster-Carr sells this this heavy duty torch (bottom of page) that will produce a 24" flame and puts out 300,000 BTUs/hr, but it would need to be connected to a bulk tank which pretty much removes the convenience aspect. So what method do you use and why?
 

BrotherBart

Modestorator
Staff member
In the first place, don't go solving a problem that you don't have yet. It will drive you crazy.

I start to sound like a broken record for the top down fire starting method but the main thing I like about it is that you get a flue warmed up fast with material that doesn't stick to the cold inside of the pipe while the kindling is catching fire and increasing the draft. Watch this video for the way to do it. It gets the draft going quick and builds a great coal bed for the long burn

http://www.ec.gc.ca/cleanair-airpur/videosWoodstove_mgt-Eng.wmv

And I don't care how many guys don't like making paper bows. If you want fast draft start-ups this is the way to go. Even or especially with a EPA exempt stove like the Englander furnace. Fire starters sitting under a pile of cold wood send a lot of unburned crap up the chimney before it gets warmed up.
 

Slow1

Minister of Fire
Nov 26, 2008
2,677
Eastern MA
300,000 BTUs/hr torch to light up a stove that puts out how many BTU's/hr max? Wow! that would be a sight.... Ok, I know you won't burn that torch for very long, but still it does strike me as a bit much although I have no idea.

Last year I only had draft troubles a couple times when the weather was not cooperating, perhaps I had wind issues? I don't know... I was able to warm my chimney by burning some newspaper and/or egg crates in the stove on top of the pile of wood. I took to doing the egg crates as I happened to have a few piled up and they burn longer than newspaper and quite hot. (and I hate doing the bow thing with newspaper!)

In general I think the idea is to get the air flowing up the chimney and keep it moving. If you warm the inside of the chimney it will feed on itself - push warm air from inside the house up it and it will warm the walls (warm being relative to the outside temps of course). Once the process gets going it should feed on itself. Until you get your system in place you won't really know if you have an issue - if you have a reverse draft then you will have a problem for sure - the more pressure you have to overcome the more heat or pressure (aka leaf blower) you will need to reverse the flow of cold air headed down it. If you are neutral to slightly positive it should not take a whole lot but may take a little bit to move the cold air out of there. Thus I don't really think you need 300K BTUs to do it.
 

summit

Minister of Fire
Aug 22, 2008
1,900
central maine
is it a masonry or prefab chimney? if its masonry, a lit piece of newspaper in the cleanout door will do the trick... if its prefab, just open the stove door and place a piece of newspaper on the baffle and light.. of course you must realize that this sort of "priming the pump" so to speak, works great untill you get to the later, cooler, stages of burning, then the flow can reverse back again..
 

Badfish740

Minister of Fire
Oct 3, 2007
1,539
Slow1 said:
300,000 BTUs/hr torch to light up a stove that puts out how many BTU's/hr max? Wow! that would be a sight.... Ok, I know you won't burn that torch for very long, but still it does strike me as a bit much although I have no idea.

Last year I only had draft troubles a couple times when the weather was not cooperating, perhaps I had wind issues? I don't know... I was able to warm my chimney by burning some newspaper and/or egg crates in the stove on top of the pile of wood. I took to doing the egg crates as I happened to have a few piled up and they burn longer than newspaper and quite hot. (and I hate doing the bow thing with newspaper!)

In general I think the idea is to get the air flowing up the chimney and keep it moving. If you warm the inside of the chimney it will feed on itself - push warm air from inside the house up it and it will warm the walls (warm being relative to the outside temps of course). Once the process gets going it should feed on itself. Until you get your system in place you won't really know if you have an issue - if you have a reverse draft then you will have a problem for sure - the more pressure you have to overcome the more heat or pressure (aka leaf blower) you will need to reverse the flow of cold air headed down it. If you are neutral to slightly positive it should not take a whole lot but may take a little bit to move the cold air out of there. Thus I don't really think you need 300K BTUs to do it.
LOL-I assure "need" was not what I was thinking-the wow factor of a 24" flame was what drew me to it ;)
 

firefighterjake

Minister of Fire
Jul 22, 2008
19,028
Unity/Bangor, Maine
I have an outside chimney (factory built metal on a first floor) and was concerned about possible drafting issues based on what I read here . . . however when I actually started burning I discovered that the draft was already quite good and pre-heating the chimney was not a necesity. Originally I was considering building a chase around the chimney for the added insulation and aesthetics . . . but after burning with it for a year I realized it's working out rather well the way it is and the only folks that can see the metal chimney is my next door neighbor and me so I've decided to leave it the way it is. My advice: try burning with the stove first to see if this will be a problem or not.
 

granpajohn

Minister of Fire
Jul 13, 2007
661
Central Maryland
I have experience with this. My (insulated, lined) masonry chim is exterior; I don't burn every day.

Have tried top down. It kinda works in mild cases of backdraft, but not usually effective. Smokes up the room. Much cussing.
Have tried heating by the usual methods, (paper on top of baffle, as mentioned above), and unusual (canned heat, propane torch). Doesn't usually work too well. And requires patience.

Best method, by far, is the use of an old hair dryer. I constructed a little snout for it out of old plastic to fit above the baffle. (Might be able to post pic later). This method works like magic. Only 30-60 seconds of blowing and the draft is usually reversed.

Which reminds me...I first test for draft by flicking a butane lighter at the edge of the baffle. Flame easily shows the direction of air flow. If up the chim; just light up. If back into the room; get out the little hair dryer. Many cold nights, the little flame is blown right out by the backdraft.

One last thing...on the wife not tending the fire every day...I've found that 24 hours is not usually long enough for things to get cold enough to reverse the draft. As long as you rekindle the fire within a day or maybe 2, I think you'll find that BB is right about a problem that you don't really have.
 

Skier76

Minister of Fire
Apr 14, 2009
1,468
CT and SoVT
That hairdryer thing sounds neat. I'd like to see a pic of that.
 

billb3

Minister of Fire
Dec 14, 2007
4,665
SE Mass
My old chimney was outside and would be tough in real cold weather. (below 10)

I'd start a real small kindling fire first with as little smoke as possible.
(sorta the same idea as top down, but usually even less smoke)
Maybe a second one.

Sometimes I'd forget or assume there were enough coals to get the next batch burning and the smoke in the living room 5 minutes later from the cold smoldering mess in the box would remind me of my fallibility.
 

FPX Dude

Feeling the Heat
Oct 4, 2007
332
Sacramento, CA
Yea, hairdryer on a cold start. No fancy "diffuser" either, hahaha...just aim it up the flue for 30-60 seconds, then light.
 

grommal

Feeling the Heat
Mar 4, 2009
487
Eastern PA
FPX Dude said:
Yea, hairdryer on a cold start. No fancy "diffuser" either, hahaha...just aim it up the flue for 30-60 seconds, then light.
We occasionally have a strongly downdrafting chimney if the stove has not been lit for a while and everything has cooled off. Trying to use a piece of burning newspaper to fix it results in a smoke-filled room. As much as I love the top-down starting method, that alone won't do it for our chimney when it's being cantankerous.

I used to use a butane torch directed into the stove pipe through the open damper on my old VC stove. After I installed the new Oslo last March, I didn't have a downdraft day before the end of the season, but I'm sure I'll experience it during the coming season. With the Oslo, I won't be able to stick the torch up into the pipe. The hair dryer solution sounds like it might work better in a case like this. If that doesn't work, maybe I'll try the leaf blower!
 

granpajohn

Minister of Fire
Jul 13, 2007
661
Central Maryland
Trying to attach the photo. (If it works...will be the first time for me)

Edit to add: YeeHaa! it worked first try!
The plastic is from an old, fairly heavy, rice cracker bag...with plenty of duct tape.
The velcro strap is an emergency medical item from fire service days. (Antique by now).
 

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Ratman

Feeling the Heat
Aug 11, 2009
458
Bedford, NH
home.comcast.net
First: OMG - You have a concerned wife and you're talking huge blow torch w/24" flame!
Please no... or Vannesa will come to your cellar and kick your butt; and since you haven't seen the video yet you will not know your only escape will be to offer her poplar and call yourself John. She will appear in an apparition to you later.

Second: Please don't watch the top-down video that our local pusher-man suggested. You will never be the same.

Third: BrotherBart does have a good common sense approach in not trying to fix something that is not broken.
 

Skier76

Minister of Fire
Apr 14, 2009
1,468
CT and SoVT
granpajohn said:
Trying to attach the photo. (If it works...will be the first time for me)

Edit to add: YeeHaa! it worked first try!
The plastic is from an old, fairly heavy, rice cracker bag...with plenty of duct tape.
The velcro strap is an emergency medical item from fire service days. (Antique by now).
Cool. I can see how that can easily direct the hot air past the baffle and up the flu. Thanks for posting.
 

polaris

Feeling the Heat
Jan 31, 2008
419
KY.
A cheap $20.00 heat gun from Harbor freight works well also. Temps are 3-4 times as high as a hair dryer.
 
I also have a problem with my exterior masonry chimney, w/ insulated liner, having a reversed draft on cold starts. Top down, and newspaper, by itself does not get the draft going in the right direction.

Hair dryer or little portable heater in the stove's side door usually works fine, but sometimes it takes 3-5 mins because the of the difficulty in forcing the air around the baffle and up the chimney.

I'm looking at a couple ways to get more positive air flow to pre-heat the liner and get a draft going.

Has anyone used the outside air kit (OAK) fitting on the secondary air and created a way to mate a heat gun or hair dryer up to the OAK? I was wondering if there is any problems with forcing hot air through the secondary air intake.
 

Skier76

Minister of Fire
Apr 14, 2009
1,468
CT and SoVT
Green Energy said:
Has anyone used the outside air kit (OAK) fitting on the primary air and created a way to mate a heat gun or hair dryer up to the OAK? I was wondering if there is any problems with forcing hot air through the primary air intake.
Yep! https://www.hearth.com/econtent/index.php/forums/viewthread/45544/

But as mentioned in the thread, it's possible to force some bad stuff out of the stove after the fire is lit and the wal-blow is still chugging along. Also, it's more air than the stove was engineer for, so like opening the ash pan door, there's a risk of overfiring.

Despite my marginal chimney set up, I never really had a problem with reverse drafts last winter. I found I could usually build a fire, light it off and all was fine. The firebox would fill with a little smoke, then the draft would start and it would clear right up.

I only had problems with reverse drafts in the fall. I attributed that to the stack effect. Our stove is in our lower level of our A-Frame and when it happened, there was a window or windows open on the main level. Again, this happened in the fall when we'd leave a window open at night. When I start a fire in the winter, all the windows are shut, except the one closest to the stove. I crack that a bit and I don't have a draft issue after doing so.

If you are having a problem with starting a fire in a cold stove, try using one of those cooking sternos. I picked a few of those up in case I ever needed to get a fire going and had a power outtage. (that was my plan b for the wal-blow). I was really surprised with how well one of those will heat up the firebox.
 

SteveKG

Minister of Fire
Jun 23, 2009
693
Colorado Rockies
I've never had a problem with our wood stoves, which have Metalbestos pipes. Regardless of temp. difference between indoors/outdoors.

With the fireplace, which has a masonry chimney, I have to open the damper for a few minutes before lighting the fire. If I do not, colder air in the chimney flows down and smokes up the house seriously. However, five minutes of open damper first solves the problem.
 

grommal

Feeling the Heat
Mar 4, 2009
487
Eastern PA
I occasionally have a downdraft when I try to start the stove (exterior masonry chimney and a less-than-optimum roofline). The traditional flue heating methods (burning paper in the flue exit, propane torch above the stove baffle, hair dryer or leaf blower, etc.) work, but it takes time to get it to turn around when it's being stubborn.

What I've found to be the most effective, when there's a breeze, is to just open an upwind door or window. The wind then forces air to flow into the house through the door/window, and it REALLY wants to flow out somewhere. Open the stove door and the flue presents the path of least resistance. As soon as it turns around, the flue has warmed enough to sustain it. No torches, no smoky paper. The only downside is that it doesn't work on a totally windless day.
 
Skier76,

Thanks for the link to the other article. It sounds like you had success with the hair dryer/OAT to pre-heat your stove/flue and get the draft going.

I understand what you mean about putting the stove under a positive pressure and the danger of doing that after the fire is lit. For me, once the draft is going up and the fire is lit, I just leave the side door cracked a little and as the flue gets hot, the nature draft takes over. No problem the draft then.

It is just getting going in the right direction if I have had a cold stove for a couple days. In the next month or two, I am going to get an OAK fitting and a heat gun as I want to get a positive air flow to speed up establishing the updraft in the flue.

Thanks for proving the concept and document it through you excellent photos. I'll let the forum know about my experience in Nov/Dec.

GE
 

laynes69

Minister of Fire
Oct 2, 2006
2,464
Ashland OH
I had the worse case scenario. An oversized exterior masonry chimney. I found the top down method is the hottest, cleanest start for me. It helps heat the baffle and it quickly gets the furnace going, even with a long path from the firebox to the flue. I now have a 5.5 rigid insulated liner in the 31' chimney so preheating will be a thing of the past.
 

Slow1

Minister of Fire
Nov 26, 2008
2,677
Eastern MA
Too lazy to go back and re-read the zombie thread to see if this was covered, but adding a few feet of extra pipe on your chimney may make a world of difference. I had an occasional issue of a 'cold wind' headed down the chimney the first year I burned. Then after adding 3' to the top of my (external classA) chimney I haven't had that problem. It hasn't seemed to hurt anything either although I haven't cleaned it yet for the 'end of season' cleaning... ok, still have until first burn to do that right? :)
 
polaris said:
A cheap $20.00 heat gun from Harbor freight works well also. Temps are 3-4 times as high as a hair dryer.
I like those, for the cheap price they do last quite a while. It's good to have your options researched but I agree on the not solving a problem until you know you have one. There are too many variables to make any one way work for everyone.

Joe likes torch idea
 

Badfish740

Minister of Fire
Oct 3, 2007
1,539
Holy wayback machine Batman! I had no idea this thread still existed ;) The ironic thing is that with 22' of Class A after the tee it turns out that my draft needs no help at all. After I installed the chimney I lit a piece of newspaper and set it on top of the baffle-it flew up the chimney as soon as I let it go. Lighting a rolled up piece of newspaper and holding it there produces a neat effect that sounds like a dull roar.
 
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