1. Welcome Hearth.com Guests and Visitors - Please enjoy our forums!
    Hearth.com GOLD Sponsors who help bring the site content to you:
    Hearthstone Soapstone and Cast-Iron stoves( Wood, Gas or Pellet Stoves and Inserts)
    Caluwe - Passion for Fire and Water ( Pellet and Wood Hydronic and Space Heating)

Wood Stove Back Drafting and Leaks within Sub-zero Climates

Post in 'DIY and General non-hearth advice' started by rogerx, Oct 14, 2013.

  1. rogerx

    rogerx New Member

    Joined:
    Oct 14, 2013
    Messages:
    4
    Loc:
    Alaska
    A common scenario I see play-out within the forums are people possibly extending their stove pipes within uninsulated areas within sub-zero climates, which causes stove pipe condensation to freeze.

    Within sub-zero climates (areas where temperatures commonly go below zero), the stove (or flue) pipe can cause condensation or gases to freeze to the insides of double wall stainless steel insulated stove pipe.

    When this scenario occurs, this highly combustible frozen creosote can reignite and cause a flash back or chimney fire down the stove pipe. More commonly, this causes a restriction for draft or combustion gases until it burns off. A very easy method for testing for this condition, stick a magnetic wood stove thermometer on the (uninsulated or insulated) stove pipe near the ceiling. During the coldest of Winter, you might start seeing some very hot temperatures if your stove pipe gases are cooling too quickly before they exit the top of the stack.

    If you live within Alaska or Canada, I find it best to insulate the stove or flue pipe as far as you can, paying particularly close attention to uninsulated attic spaces, and try to not go further then one or two feet above an uninsulated space. (However, stacks need to also be above the peaks of the roof, or properly sized.)

    Another solution commonly used within Alaska and Canada, removing the rain cap. Albeit, I hate doing this but anything above the flame causes restriction, causing gases to gather versus rapidly escape and further freezing at the rain cap and not just to the inside of the stove pipe.

    I commonly see posts within the forum where people are complaining of leaks and other problems, and all follow-up comments seem to completely miss this dangerous scenario! Yes, you can burn a hot fire every so often, but with -40F to -60F, it is quite a futile effort at managing this scenario.

    Within my garage where I installed an oil boiler, I ran the stack straight up through to the roof without any bends, and through an uninsulated attic space. Within the uninsulated attic space, I fabricated a four inch blue styrofoam (2 x 2" styrofoam boards) wall around the stack with the required spacing for mitigating any heat from the flue pipe. I also used a batt of Rock Wool for insulating just below the sheet metal roof, within the inside ceiling of this fabricated styrofoam walled structure around the flue pipe. The stake exits out the peak of the garage roof, about one to two feet above the peak. Now during the middle of Winter here with this particular install during weeks of -40F to -60F, I find I now have very little drips of icing at the top rain cap. I really just wish I would have insulated around my wood stove pipe within the house attic the same way several years ago when I was repairing the main house roof!

    *NOTE: I usually find it's also best to usually go straight-up through the roof with the fewest bends as possible, as anything above a flame will cause pressure to build within the combustion chamber. (ie. Anything above a flame, will cause pressure within the combustion chamber to significantly increase, while also being exponentially more sensitive to negative pressures around the heating device.) And any bends or angles used in the flue or stove pipe will be areas where gases will build and/or possibly cause decreasing temperatures for combustion gas when compared to a straight up-through the roof installation.

    **NOTE: Make sure there is adequate combustion air provided for the heating device being installed. Also note super cold air usually falls, and having a basement will allow cold air to fall into the basement during Winter. The same dynamics of pipe sizing and bends, tends to also apply to intake air. For my house intake combustion air, I also added a simple four inch 110v fan with a wall switch wired in the wall near the wood stove.

    Hopefully those searching the Internet will come across this post, and find this very useful!

    Helpful Sponsor Ads!





  2. Highbeam

    Highbeam Minister of Fire

    Joined:
    Dec 28, 2006
    Messages:
    9,132
    Loc:
    base of Mt. Rainier on the wet side, WA
    Supercharger?
  3. rogerx

    rogerx New Member

    Joined:
    Oct 14, 2013
    Messages:
    4
    Loc:
    Alaska
    Humorous. ;-) Although understandable if you're within the Lower 48 only experiencing +31F Winter temperatures.

    Didn't want to elaborate or explain this part of my system, as I was trying to keep this article focused on a main issue with sub-zero freezing combustion gases, but here's my explanation on the combustion air.

    I initially installed the combustion air supply going through the basement wall several years ago as an experiment, but while knowing I had to have some make-up air being supplied from someplace during -40F to -60F cold periods, and mainly for an oil furnace using a side-shot fan venting system installed during escrow. So I dug a trench four feet down and ran a four inch ABS pipe to a point of clean air. (Clean air within Alaska during cold periods is a commodity.) I placed down either two or four inches of styrofoam over the ABS piping, hence insulating against the cold air above ground while utilizing ground warmth to temper the incoming air. The run had several bends, and I realized the super cold air during the cold periods would force itself into the house. I later found I needed a fan during warmer periods. The incoming -40F/-60F air is now tempered to approximately +15F. Imagine had I ran copper piping? (I also have an electric clothes dryer within the house.)

    I speculate those within the Lower 48 only experiencing +31F during Winter, would likely not experience the exponential benefits of such a system (ie. cost to benefit), and could likely benefit far more from a simple heat exchanger.

    And with the newer wood stoves these days placing objects over the flame causing more pressure within the combustion chamber, maintaining a slightly more positive pressure around the exterior of the combustion chamber seems to be exponentially more important than an older heating device without objects placed over the flame.
  4. Highbeam

    Highbeam Minister of Fire

    Joined:
    Dec 28, 2006
    Messages:
    9,132
    Loc:
    base of Mt. Rainier on the wet side, WA
    Are you kidding? We had 30 degrees last week here in the moderate northwest. Single digits easily every year. No not as cold as AK, but certainly not 31F. I expect that there are parts of the lower 48 that are extremely cold like up in the dakotas or even Maine.

    Have you ever been out of AK?
  5. rogerx

    rogerx New Member

    Joined:
    Oct 14, 2013
    Messages:
    4
    Loc:
    Alaska
    Last edited: Oct 16, 2013
  6. Highbeam

    Highbeam Minister of Fire

    Joined:
    Dec 28, 2006
    Messages:
    9,132
    Loc:
    base of Mt. Rainier on the wet side, WA
    Silly guy, average temperatures mean nothing when your pipes are frozen. The average speed of my truck is like 30 mph but I don't want a truck designed to only go 30 mph.
  7. pen

    pen There are some who call me...mod. Staff Member

    Joined:
    Aug 2, 2007
    Messages:
    7,107
    Loc:
    N.E. Penna
    I must have somehow missed this common occurrence. Hmm
    oldspark likes this.
  8. oldspark

    oldspark Guest

    It gets plenty cold here in Iowa and never heard of that happening, been burning over 30 years, 31 degrees is a heat wave here in the winter.
    PapaDave likes this.
  9. TradEddie

    TradEddie Minister of Fire

    Joined:
    Jan 24, 2012
    Messages:
    724
    Loc:
    SE PA
    OK, I have regrettably never been to Alaska, never experienced anything colder than -15F, and never anything colder than 0F at my own house, but if you are burning a modern stove properly there should not be any significant creosote in the flue gases in the first place. If you are burning any stove badly you'll get dangerous creosote condensing in your chimney even at +50F.

    Don't blame the cold, blame the burner. OTOH, nobody here would argue with insulating a flue as much as possible.

    TE
  10. rogerx

    rogerx New Member

    Joined:
    Oct 14, 2013
    Messages:
    4
    Loc:
    Alaska
    Anything subjected to the colder then -20F temperatures, pretty much freezes instantly. (ie. Liquids, gases, etc.) I have seen some of the high efficiency oil and propane burners outputting combustion gases higher in humidity then that of 86% efficient oil and propane burners, and then freezing on the exterior vent pipe when experiencing even Lower 48's mild temperatures of Winter. There's a lot of factors to consider here.

    People tend to burn pine and birch here within Alaska. Burning 24/7 rather then one fire a night, also condones any build-up quite readily.

    Comparing my experience within the Lower 48 northern states, having to burn 24/7 for almost six months straight is significantly more wood stove usage then required to heat a structure within the Lower 48. (Depending on the wood stove used, cleaning the chimney every two months might be necessary.)

    Having experience with subzero temperatures might help, rather than just concluding. Personally, I do not rule-out anything until I see proof.

    Something I see sometimes, people running their stacks on the exterior of their house, and up two to three stories above the roof tops with only the one inch insulation provided by current insulated chimney stove (or flue) pipe on the market. Shrugs. If the gases ever freeze, and I speculate they do and they're oblivious to the scenario, then this danger is completely hidden by the long runs of flue or stove pipe. (Experienced people within the area have already stated condensation does form on the inside, and melts and runs back down during winter.) I have seen some smarter folks, encasing these extended runs within a secondary exterior wall with house siding.

    When living within extremes, your little problems can become very large problems within this area, very quickly. In other words, some of the hardware manufactured to State codes within the Lower 48, likely are not adequately made to experience the extremes of Canada and Alaska. Matter of fact, Anchorage or southern Alaska is quite mild, when compared to northern Alaska.
  11. woodgeek

    woodgeek Minister of Fire

    Joined:
    Jan 27, 2008
    Messages:
    2,727
    Loc:
    SE PA
    The amount of heat going into the stack varies with how the stove is operated. Some folks are tamping down a cool burn and loading their chimneys with creosote when the temp outside is 45F. In AK, I could open her up a bit and keep an uninsulated flue clean at -20F. Outside temp is just one factor to a clean chimbley.

    Oh yeah, folks in every state in the lower 48 will claim to get as cold as Alaska sometimes. At least it will **feel** that way when you are just wearing jeans and a thin sweater. ;lol
  12. TradEddie

    TradEddie Minister of Fire

    Joined:
    Jan 24, 2012
    Messages:
    724
    Loc:
    SE PA
    There is a world of difference between ice and creosote. I've seen ice form on a HE propane exhaust at 20F, never mind -20F (BTW the reason HE furnace exhaust has higher humidity is because it is colder, so higher %RH), but I still maintain that having dangerous levels of creosote forming is the result of poor burning habits, not the insulation on the pipes or the outside temperature.

    TE
  13. Backwoods Savage

    Backwoods Savage Minister of Fire

    Joined:
    Feb 14, 2007
    Messages:
    27,816
    Loc:
    Michigan
    Welcome to the forum Roger.

    We have others from Alaska on this forum and you are as welcome as they and they are some pretty good folks. However, you need to change your perception of what happens outside of Alaska. Especially your claim of people having fires only at night. Sorry, that is true only in early fall and late spring. I apologize to you as I have not experienced outdoor temperatures colder than -52. However, I have never had the problem that you are writing about. The chimney continues to draw very well and we don't get creosote in our chimney. The gasses do not freeze in the chimney. That flashback you are writing about is not caused by creosote although it can be caused by the chimney temperatures being too low. The flashback is simply unburned gasses ignighting in the firebox. This is usually caused by two things; burning too low of a fire and more usual, burning wood that has not been properly dried. Nuff said.
    Highbeam likes this.
  14. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,348
    Loc:
    SW Virginia
    Well said Dennis.
    Last edited by a moderator: Oct 24, 2013
    Backwoods Savage likes this.

Share This Page