thechimneysweep
Minister of Fire
Frank, you're still chewing this bone after how many years now? Good to have you back, and to see you finally put your stove to the test and observed the EBT in action (although your temp range for actuation was probably a little skewed, due to the cooling affect created by the open ash drawer).
Your test exactly illustrates what I've been trying to explain on my website at http://www.chimneysweeponline.com/hoebt.htm the whole time. I think one problem people have grasping the concept as I present it might be my lifelong inability to explain things very well. It could also have something to do with the illustrations: in order to fully show the EBT in action, it took me several diagrams, which might make it seem like the EBT is operating throughout the entire burn cycle. As you've learned for yourself, this is not the case. Meanwhile, I can't be too far off base, because the tech support people at PE tell me that when people call them for a description of the EBT technology, they send them to my website. Nonetheless, I find myself continually working on that page, and hope someday to end up with a more concise and easily understood description of the device and what it does.
The one issue you still seem to have a hard time grasping is how the EBT results in extended burn times. Let me take another whack at it for you.
Say you're a manufacturer, and want to come out with a Big Dog; a non-catalytic stove that is capable of 90,000+ btu output and can heat up to 3,000 sq.ft. In order to heat that large an area, your stove is going to have to accomodate large loads of wood and maintain surface temps in the 700+ range for a good portion of each burn cycle.
The problem is, when you reload a stove that's burning at that temperature, the fresh load tends to gasify extremely quickly, and it takes a lot of extra combustion air to burn the resulting bloom of volatiles. Thus, your Big Dog isn't going to pass EPA emissions testing at low draft setting after the mandated reload.
Other manufacturers of large, high output non-catalytic stoves have "solved" the EPA test problem by taking away the low end on the draft control, so there is considerable airflow to the fire even when the draft control is adjusted as low as it can go. This technique might get the stove through testing, but causes extra air to be supplied to the fire during all stages of the burn cycle, even when it isn't needed, which has resulted in consumer complaints of short burn times for non-catalytic large-firebox models.
As it happens, the "bloom" of gasified volatiles from a fresh load on an already-hot fire raises the temperature of the stove considerably. Now, as a manufacturer, what if you could incorporate a device in your Big Dog that would sense that increased temperature level and supply extra air to the fire only during that portion of the burn? The device would open up and supply extra air until the extra volatiles were consumed, then sense the ensuing drop in temperature, and close back down. To prevent an out-of-control situation, the device would be designed to also close down should the stove approach overfire temps. This would enable you to incorporate a draft control that could be closed down to just a slit for long burn times immediately after the fresh load was kindled, and still pass EPA testing. Since your Big Dog would therefore be able to create much longer burn times than the other Big Dogs in the yard, you could justifiably refer to your device as Extended Burn Technology.
Many owners of PE stoves equipped with EBT might not need it very often, because they're not heating 3,000 sq.ft., and don't need to work their beasties very hard: they're able to heat their houses while putting along at 300-600 degree stovetop temperatures. When they add a fresh load at that temperature range, the wood gasifies much more slowly, and there's no "bloom" or resulting temperature peak high enough to actuate the EBT mechanism. Nonetheless, the mechanism remains vigilant, and will kick in when needed, as observed by the surprised jwscarab in another recent post. Meanwhile, all owners of PE's Big Dog firebox enjoy the longer burn times created by a draft control that can be turned down to a truly low setting.
Your test exactly illustrates what I've been trying to explain on my website at http://www.chimneysweeponline.com/hoebt.htm the whole time. I think one problem people have grasping the concept as I present it might be my lifelong inability to explain things very well. It could also have something to do with the illustrations: in order to fully show the EBT in action, it took me several diagrams, which might make it seem like the EBT is operating throughout the entire burn cycle. As you've learned for yourself, this is not the case. Meanwhile, I can't be too far off base, because the tech support people at PE tell me that when people call them for a description of the EBT technology, they send them to my website. Nonetheless, I find myself continually working on that page, and hope someday to end up with a more concise and easily understood description of the device and what it does.
The one issue you still seem to have a hard time grasping is how the EBT results in extended burn times. Let me take another whack at it for you.
Say you're a manufacturer, and want to come out with a Big Dog; a non-catalytic stove that is capable of 90,000+ btu output and can heat up to 3,000 sq.ft. In order to heat that large an area, your stove is going to have to accomodate large loads of wood and maintain surface temps in the 700+ range for a good portion of each burn cycle.
The problem is, when you reload a stove that's burning at that temperature, the fresh load tends to gasify extremely quickly, and it takes a lot of extra combustion air to burn the resulting bloom of volatiles. Thus, your Big Dog isn't going to pass EPA emissions testing at low draft setting after the mandated reload.
Other manufacturers of large, high output non-catalytic stoves have "solved" the EPA test problem by taking away the low end on the draft control, so there is considerable airflow to the fire even when the draft control is adjusted as low as it can go. This technique might get the stove through testing, but causes extra air to be supplied to the fire during all stages of the burn cycle, even when it isn't needed, which has resulted in consumer complaints of short burn times for non-catalytic large-firebox models.
As it happens, the "bloom" of gasified volatiles from a fresh load on an already-hot fire raises the temperature of the stove considerably. Now, as a manufacturer, what if you could incorporate a device in your Big Dog that would sense that increased temperature level and supply extra air to the fire only during that portion of the burn? The device would open up and supply extra air until the extra volatiles were consumed, then sense the ensuing drop in temperature, and close back down. To prevent an out-of-control situation, the device would be designed to also close down should the stove approach overfire temps. This would enable you to incorporate a draft control that could be closed down to just a slit for long burn times immediately after the fresh load was kindled, and still pass EPA testing. Since your Big Dog would therefore be able to create much longer burn times than the other Big Dogs in the yard, you could justifiably refer to your device as Extended Burn Technology.
Many owners of PE stoves equipped with EBT might not need it very often, because they're not heating 3,000 sq.ft., and don't need to work their beasties very hard: they're able to heat their houses while putting along at 300-600 degree stovetop temperatures. When they add a fresh load at that temperature range, the wood gasifies much more slowly, and there's no "bloom" or resulting temperature peak high enough to actuate the EBT mechanism. Nonetheless, the mechanism remains vigilant, and will kick in when needed, as observed by the surprised jwscarab in another recent post. Meanwhile, all owners of PE's Big Dog firebox enjoy the longer burn times created by a draft control that can be turned down to a truly low setting.
. That's a good thing and I'm glad they have addressed the high temp range. The stove really does work well over a wide temp range and it's nice to have it able to kick butt when needed. But then, my issue has not been with getting it hot. Believe it or not, this winter in the Pac NW has been cold enough where we have packed the stove full to the brim many days and nights. The stove has been up in the 700 degree range several times. At that time we do see the afterburners kick in and push the stove towards 750. However, when burning softwood, this excitement can be short lived. The stove rarely holds that temp for long. Next year we should be burning hardwood, but that is not often available out here. 
