We have a Blaze King woodstove that has been our main source of heat in our house for about 5 years. The King is in the basement. Off the top of the stove, we have double wall black pipe. About 6' above the woodstove there is a 90 elbow, then a short piece of horizontal pipe until the transition to SST insulated double wall pipe. The insulated pipe then passes through the exterior wall of the house and into a chimney chase framed on the outside of the house. At the wall penetration where the insulated pipe passes through the wall, an insulated wall thimble is used. The pipe then turns 90deg upward at the wall support via an insulated Tee and Plug. There is about 25' of vertical insulated pipe in the chase, then a standard cap. We have been burning standing dead lodgepole since the stove was new. All of our firewood comes off some nearby property and our wood storage, wood splitting, wood species has all been consistent for the last 5 years. I mention that to rule out the fuel as being a variable.
We have recently had a couple close calls with the insulated pipe getting so hot inside the chase that it has charred the framing that makes up the chase. The chase itself is 2x4 framing, with batt insulation. The insulated pipe has more than 2" of clearance to any of the wood framing and a fire stop joist shield is utilized at the floor penetration in the chase. There is only evidence of charring of the framing at the floor of the chase where the fire stop joist shield is located. Our standard burning procedures are to do a hot burn in the morning getting the stove well into the active stage by the temperature gauge that is located on top of the blaze king. We burn it hot for at least 20 min, then stock it full of wood, engage the catalytic bypass, damp the air and allow the stove to burn all day. When we return to the house after work, the stove is easily still in the active zone on the temperature gauge. We sweep the chimney every year and get very minimal build up - a small pile of dust is about all we get.
Year after year, the stove has performed great: good draft, easy to start, nice controlled burn. Until the day after christmas this December. We had allowed the fire to die completely the day prior and started from scratch that morning. We got a small fire started in the stove using our standard procedure of newspaper/kindling. Once the fire got started we filled the firebox and started the hot burn - catalytic was not engaged. We started to smell a burning plastic smell. Upon investigation, the firebox appeared normal with a vigorous hot fire, the temperature seemed reasonable with it registering in the active zone, but not pegged, the chimney cap appeared normal - no flames, and no whooshing sounds of air that I have heard a chimney fire can be explained by. Even though all seemed normal, the inside of chimney chase got really hot. We ended up opening up the sheetrock on the inside of the house to gain access to chase for further investigation. That is when we discovered the charred framing along the floor of the chase. Although the charring was minor, it was enough that you could smell smoke inside the chase and the batt insulation.
We kept the wall open to the chase to allow monitoring of the outside wall of the pipe. Using a laser infared temp gun we have kept track of the chimney pipe temp inside the chase and note that with the condition of the stove (i.e. temp guage reading on the stove, is the catalytic engaged, is it damped, etc). On a normal burn, the exterior of the chimney was measuring between 120 and 160 deg. One other time, under very similar circumstances to the day after christmas (hot burn, no catalytic engaged), the pipe got real hot and measured 384. At this temp, the framing in the chase was just starting to smolder and when I sprayed the framing down with water, it steamed and sizzled.
Things we have done to trouble shoot:
1) hired a local certified chimney installer/sweeper to inspect the entire installation. All clearances and proper installation were verified
2)We have recently replaced the temperature gauge just to ensure we were reading proper temperatures on the stove.
3) inspected the insulated pipe for damage, it all looks clean, straight, no warpage, no creosote build-up.
We can't find anything wrong with the installation or our process of burning the stove, but yet we are obviously experiencing some extreme heat inside the chase.
On both instances where the chimney got HOT, the plug at the bottom of the clean-out tee was loose and creating about a 3/4 inch opening around the perimeter of the plug. The bottom of the chase is open to exterior ambient air until the floor joists. Is it possible that this opening was a fresh air source and that due to the fact that the catalytic was not engaged that there was enough combustibles left in the flue gas/exhaust that it was reburning the flue gas inside the chimney? This would explain why there was no "whooshing" sound of air, but yet still explains how a chimney fire was occuring with no creosote present.
Since that time, we have secured the plug tight into the cleanout and not had any issues. We have deliberately created some really hot fires to test this theory and the hotest the chimney measured was about 254, with no smoldering of the framing and no smoke smell inside the chase. Our ultimate goal is to build our confidence that we have located the problem, fixed it and can move on with patching the sheetrock in our house.
Thanks for reading this long post and offering up your insight and suggestions.
We have recently had a couple close calls with the insulated pipe getting so hot inside the chase that it has charred the framing that makes up the chase. The chase itself is 2x4 framing, with batt insulation. The insulated pipe has more than 2" of clearance to any of the wood framing and a fire stop joist shield is utilized at the floor penetration in the chase. There is only evidence of charring of the framing at the floor of the chase where the fire stop joist shield is located. Our standard burning procedures are to do a hot burn in the morning getting the stove well into the active stage by the temperature gauge that is located on top of the blaze king. We burn it hot for at least 20 min, then stock it full of wood, engage the catalytic bypass, damp the air and allow the stove to burn all day. When we return to the house after work, the stove is easily still in the active zone on the temperature gauge. We sweep the chimney every year and get very minimal build up - a small pile of dust is about all we get.
Year after year, the stove has performed great: good draft, easy to start, nice controlled burn. Until the day after christmas this December. We had allowed the fire to die completely the day prior and started from scratch that morning. We got a small fire started in the stove using our standard procedure of newspaper/kindling. Once the fire got started we filled the firebox and started the hot burn - catalytic was not engaged. We started to smell a burning plastic smell. Upon investigation, the firebox appeared normal with a vigorous hot fire, the temperature seemed reasonable with it registering in the active zone, but not pegged, the chimney cap appeared normal - no flames, and no whooshing sounds of air that I have heard a chimney fire can be explained by. Even though all seemed normal, the inside of chimney chase got really hot. We ended up opening up the sheetrock on the inside of the house to gain access to chase for further investigation. That is when we discovered the charred framing along the floor of the chase. Although the charring was minor, it was enough that you could smell smoke inside the chase and the batt insulation.
We kept the wall open to the chase to allow monitoring of the outside wall of the pipe. Using a laser infared temp gun we have kept track of the chimney pipe temp inside the chase and note that with the condition of the stove (i.e. temp guage reading on the stove, is the catalytic engaged, is it damped, etc). On a normal burn, the exterior of the chimney was measuring between 120 and 160 deg. One other time, under very similar circumstances to the day after christmas (hot burn, no catalytic engaged), the pipe got real hot and measured 384. At this temp, the framing in the chase was just starting to smolder and when I sprayed the framing down with water, it steamed and sizzled.
Things we have done to trouble shoot:
1) hired a local certified chimney installer/sweeper to inspect the entire installation. All clearances and proper installation were verified
2)We have recently replaced the temperature gauge just to ensure we were reading proper temperatures on the stove.
3) inspected the insulated pipe for damage, it all looks clean, straight, no warpage, no creosote build-up.
We can't find anything wrong with the installation or our process of burning the stove, but yet we are obviously experiencing some extreme heat inside the chase.
On both instances where the chimney got HOT, the plug at the bottom of the clean-out tee was loose and creating about a 3/4 inch opening around the perimeter of the plug. The bottom of the chase is open to exterior ambient air until the floor joists. Is it possible that this opening was a fresh air source and that due to the fact that the catalytic was not engaged that there was enough combustibles left in the flue gas/exhaust that it was reburning the flue gas inside the chimney? This would explain why there was no "whooshing" sound of air, but yet still explains how a chimney fire was occuring with no creosote present.
Since that time, we have secured the plug tight into the cleanout and not had any issues. We have deliberately created some really hot fires to test this theory and the hotest the chimney measured was about 254, with no smoldering of the framing and no smoke smell inside the chase. Our ultimate goal is to build our confidence that we have located the problem, fixed it and can move on with patching the sheetrock in our house.
Thanks for reading this long post and offering up your insight and suggestions.
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