Kent Tile Fire (and Sherwood) stoves

[precaud]

I just finished installing a Kent Tile Fire in superb condition that I bought last weekend. I (and many others) had a very positive experience with this stove back in the mid/late 80's. It also has a unique place in stove design history: It is the progenitor of all of the modern steel EPA stoves with glass fronts, airwashes, and secondary combustion. Besides all that, it was robustly built and should be extremely durable under normal use. So I decided to start a thread to go over some of its important details, and to see how it stacks up against the Quad 2100M ACT, a modern, extremely efficient and clean-burning EPA stove which just happens to have the exact same firebox dimensions. The Quad has been the primary heater in the upstairs of my home for most of the last 4 years, so it's a very familiar quantity, and will provide a very tough compare.

I also included the Sherwood in the thread title. The Sherwood doesn't have the Tile Fire's convection shell and has a different rod/handle to control the damper. But other than that, they are functionally identical stoves.

Attached is a pic of the TF installed on my hearth and ready to burn. Definitely straight from the 80's! I burned a small fire in it this afternoon to drive any moisture out of the bricks. First "real" fire will be tonight - in a couple hours or so.

 

[BrotherBart]

Enchanting.

 

[precaud]

First, a few technical details not mentioned in the manual that should be useful for understanding. maintaining, and troubleshooting a Tile Fire/Sherwood.

The first pic is the secondary chamber baffle at the top of the firebox. There's a lot going on in this chamber so it deserves a close look. The air/flame/smoke gets mixed together while being pulled through the holes on their way to the chimney pipe. This 'forced mixing' is not common in more modern stoves, which instead provide an excess of air to aid secondary combustion.

The next pic is a tad out of focus and requires some explanation. It is looking through the chimney connector to the inside of the secondary chamber. The mirror is positioned so you can see inside toward the front of the chamber. There you can see a steel plate (B) which is placed a couple inches behind the holes and covers all but the outer 2.5" on either side. The flames/air/smoke gets pulled through the holes and is forced to mix in this 'mini-chamber' before exiting through the small openings (A) on either side of the plate into the larger chamber and then out the chimney. Simple but effective.

Tom Oyen gave good instructions on checking the damper control rod in this thread:
https://www.hearth.com/talk/threads/65588/

The next two pics show the bypass damper in open and closed positions. Yours should be able to move between these two positions easily. The steel plate serves as a stop for the damper in full open position. The damper "puck" floats on the baffle surface and on the control rod end (i.e. it is not attached to the rod) so it should accommodate a reasonable amount of warpage of the chamber bottom.

One thing about this secondary chamber is that a significant amount of fly ash accumulates up there with use. My stove accumulated 3 shovels full of very fine ash in 10 or so seasons of mild use. That's quite a lot. Cleaning/vacuuming out the ash should be a part of your annual maintenance.

I first used a plastic kitchen spatula to scoop the ash into the firebox below. While doing so, I unknowingly pushed some of the ash between the damper "puck" and the steel plate. I then tried operating the damper control rod, and it was binding toward the full open position. Odd, since it wasn't binding before I cleaned. So I vacuumed out the area behind the puck, and then it operated smoothly again. So if yours is binding, clean out this area in front of the plate before you pronounce your baffle warped.

 

[begreen]

Nice stove indeed. It will be interesting to see how your modern tweaks improve operation. Fire her up!

 

[precaud]

I have the doors open, cooling the house down so I can fire it up! It was a sunny day here, and the solar heaters had the place up to 76F...

 

[precaud]

The Tile Fire firebox and secondary chamber are made from 1/4" steel - great for efficient heat transfer; not good for maintaining the high firebox temperatures needed for clean burning. The bottom of mine is the only surface that showed any signs of warpage, so clearly it could use some protective insulation.

I have some Thermal Ceramics K-28 lightweight insulating fire brick (2800F service temp, 51 lbs/cu ft density, K=0.97/in. @ 1000F, standard size, better shock resistance than pumice bricks). I sliced them in half on a tablesaw using a 10" masonry blade to 1-3/16" thick, just slightly less then the standard "splits" used in other wood stoves. These bricks are much lighter (less than 1.5 lbs each) and have far superior insulating characteristic compared to standard bricks. It took 18 splits to line the stove sides, back, and bottom to a 9" height. I may try lining the remaining top part of the sides and back after I see how this works out.

The Tile Fire weighs 230 lbs (about 30 of which is the tiles), plus 27 lbs of added firebrick = 257 lbs. This compares to the Quad 2100 listed at 320 lbs. The weight difference was obvious when moving them. This should enable the TF to produce useable heat more quickly, and the Quad to retain heat longer. But the Quad's firebox is better insulated, so that gives it some advantage in warmup. We shall see.

 

[BrotherBart]

Did you mic the plate steel in that stove? How in the heck does that much quarter inch plate only weigh 200 pounds? Most of that Quad is 3/16".

 

[precaud]

No way to mic the shell, the brochure says it's 1/4". Just measured the 2ndary chamber baffle, it is 9mm which is just under 3/8".

Remember, the Quad has steel channels inside and outside the firebox for its four air sources. That adds a lot of weight. And a 5/16" top plate.

 

[precaud]

I've burned four loads in the stove, and can see its character emerging. I think it's best to describe it in two different contexts: first, as a heater, and second, as a wood burner (i.e. how well does the firebox work), both as compared to the Quad.

As a heater, and specifically as a convection heater, it is really quite impressive. It warms up and starts producing significant amounts of heat amazingly quickly. It's convection design is the best I've ever experienced: the brick walls of the hearth right next to it get barely warm to touch. I'd say the clearance figures given in the manual are on the conservative side. Most impressive is how much better it distributed heat to other rooms, raising them by 2-3 degrees compared to the Quad. This stove is an aggressive convector with comparatively little direct radiation. As a heater, it rocks.

As a wood burner, the situation is more complicated. In it's day, it was revolutionary. But fireboxes have evolved significantly since then. Compared to the Quad which, again, is also a north/south burner with the exact same firebox dimensions, the Kent is a fussier stove to use. You absolutely must leave an inch or so space between logs or else it will not burn in the back. With no separate secondary air, there must always be flames reaching up from the logs to ignite the gasses up above. There are no prolonged "floating secondary burns" like some EPA stoves can do. And this in turn means that the minimum burn rate is higher - no lazy, lingering flames with this stove. It needs a higher minimum airflow to keep things burning.

This compared to the Quad, which will eat anything and burn it clean. A load of two large rounds will give a nice, controlled flaming burn for 3 hours or more. The Kent won't do this at all. It generally prefers smaller splits and an absolute minimum of three at a time. This is where the Quad's doghouse air, secondary air, and fully insulated firebox makes the difference. Just as with a chimney, the insulation makes the most difference at low burn rates.

After closing it down before going to bed last night, there were plenty of coals to start up again this morning with just a few sticks of kindling placed on top to ignite. Very nice. Temps in the house this morning were the same as with the Quad, which suggests that the total heat output was not really different from the Quad's; the Kent just puts out more heat while it's burning. This is consistent with its lighter weight and less-insulated firebox.

I checked for smoke output regularly while it burned, and more often than not, there was some visible smoke coming out of the stack - not dense smoke, but visible. There was smoke until the front of the secondary chamber heated up; it was easy to tell when this happened - the carbon that collected on the front of the baffle around the holes started to burn off. From then, through most of the rest of the burn, it was cleanest, and then grew a little worse as it burned the wood at the rear of the box. This is where the lack of a separate secondary air source really took its toll. And it would have been worse without the firebrick I added. Just like other deep stove geometries I've seen which have no air at the rear of the firebox, you can't have combustion without air. I'd bet that adding even rudimentary secondary air inlets at the rear of the box would work wonders with this stove.

I'm not going to experiment any more with it for now. Insulating the top of the firebox isn't going to helps matters. Adding secondary air is what it needs.

It's been fun revisiting this old friend. It's a superb heater. The designer who created it back in the 80's deserves our thanks and a toast.

 

[agartner]

Awesome thread, very well done. I can't argue with your observations - I also added the firebrick to the inside of my Sherwood with very good results as well. As the Sherwood does not have the convection shell, it's mostly a radiant heater, and it does it well. Adding the firebrick did make things a lot less harsh. One experience I don't necessarily share is the "back-burn" of the stove. I find that the back burning characteristics of the stove is good, and as long as the temps are right inside the firebox, you get a really nice secondary burn lightshow dancing off of the bottom of the secondary burn chamber. I also find my stack is almost always smokeless, but I need to temper that statement with the fact that I am using Bio-Bricks instead of cordwood, which have a dead low moisture content and burn like nobody's business. All in all, great observations. I know last year I was really looking to replace the Sherwood with a more 'updated" EPA stove but instead decided against it. I never knew about the additional plate in the secondary burn chamber. That explains why the stove will bellow smoke out the front door if you don't open that bypass before cracking the door. I've forgotten a few times but am always quickly reminded!

When I got a chance, I'll snap a few pics of the sherwood, for anything, to note the differences between it an the TileFire.

 

[precaud]

Pics of your Sherwood would be great Al, please do.

I can see how the bio-bricks might work well in these stoves. Their smaller size and controlled content would make for predictable fires load after load.

 

[begreen]

Great to see this information about these pioneering stoves. Thanks for the great info.

It would be helpful to add an article to the Kent stove wiki. Anyone up for that? I can copy/paste, but it would be nicer as a full article both on the original stove and on the mods to bring it up to modern burning standards. If you need some help, let me know.

https://www.hearth.com/econtent/index.php/wiki/Kent_Tile_Fire/

 

[daleeper]

Nice looking stove, looks like the hearth was made for it, and good writeup.

 

[precaud]

Did some digging last night, hoping to find some test data on the Kent stoves. I found this 1986 one, by the guy who I learned alot from back in the 80's, Jay Shelton. Pretty thorough test comparing the Tile Fire to a BK catalyst, Lopi, open fireplace, and some more conventional heaters, using different wood types, burn rates, etc.

http://www.arb.ca.gov/research/apr/past/a3-122-32.pdf

I haven't read it in detail yet, only scanned quickly through it. The Tile Fire he used was a "Mk II" which had the firebrick and stainless steel shield inside. It also reminded me that I bought the Sherwood after hearing him speak enthusiastically about it.

One thing I hoped to see but didn't are charts of output rate vs time for the burn cycle.

 

[begreen]

Jay also authored the Woodburner's Encyclopedia published in 1976. It went through several publishings and is still available used at book shops and via Amazon.

 

[precaud]

Yep. His Solid Fuels Encyclopedia has long been a reference for me. I just looked in the phone book; he still lives here.

I'd like to find out more about the SS plate that was part of the Mk II upgrade kit. If anyone has seen one, a description would be appreciated. A photo would be awesome!

 

[Battenkiller]

Did some digging last night, hoping to find some test data on the Kent stoves. I found this 1986 one, by the guy who I learned alot from back in the 80's, Jay Shelton. Pretty thorough test comparing the Tile Fire to a BK catalyst, Lopi, open fireplace, and some more conventional heaters, using different wood types, burn rates, etc.

It's pretty cool that you got to hang with one of my wood burning heroes. We had him back east in the 70s, but I never heard him speak. His book "The Woodburner's Encyclopedia" that I got back in my hippie days is still the bible to me, and the source for 90% of the graphs and tables I post here on Hearth.

That study is pretty intense, and I'd recommend almost anybody who is interested in these things to take a few hours to go through it. It appears to be one of the very few scientific comparisons between the old stoves and the developing new technologies. Of special interest to me, an unnamed stove whose rough schematic identifies it as an early Vermont Castings downdraft design was used, but unfortunately, they used it only as a conventional updraft airtight, and as an open fireplace (i.e. Franklin stove). Even then, as an airtight it didn't do so bad, especially with green oak (which it burned considerably cleaner than the dry stuff, but with a slight hit in the total efficiency department). I really wish they tested it with the bypass closed and in secondary combustion mode.

Anyway, Precaud, I'm glad you get to enjoy some nice heat from a familiar friend. As for me, I can't say I'd want to go back and burn in that oval sheet metal Ashley that got me started in all this.

 

[precaud]

Yes, "intense" is a good word for it. I still haven't made it all the way through.

About the VC stove: Since the stoves were chosen on the basis of the California chimneysweeps surveyed, along with the project manager, it's possible that 'updraft' and 'open' represent the ways it was most often used in that area. Back then, the downdraft mode had a reputation for being very finicky.

Some notes on the Tile Fire in the test: The doug fir blocks burned cleaner than the seasoned oak. The fir loads were four pieces, ~2.5 lbs each piece; the oak loads were five pieces ~3.5 lbs each. The fir loads are 2x4's with 1.5" space between them. This fits what I've seen so far: this stove likes to burn small, hot loads, with plenty of air space between each log. I filled it up tonight and that turns it into a smoke dragon - simply not enough free air for secondary combustion, and the air is unable to penetrate to the rear of the stove.

An altered procedure for cold start with fir was used with the Kent - the first main load was simultaneous with the kindling load. The reason is not explained.

After watching the TF burn the last couple days, I decided to line the rest of the side and back walls under the baffle. It definitely raised temps in the firebox, I could even feel more heat from the glass. And it brought the secondary chamber up to temps more quickly. However, it only helped clean up the burn in the stages where it already burned the cleanest. It did nothing to help the first 20-30 minutes, when the surface volatiles are being burned off. Not until after that does it settle down and burn more cleanly. And it doesn't help to give it more primary air - that only stimulates the fire more. With only one air source, that's the main Catch 22 with this stove.

This early-stage dirty burn is made worse if the wood length is near the maximum. The flames from the forward ends have nowhere to go but directly up and out the baffle, with no chance to mix with any air, producing prodigious amounts of smoke. Not good. The best results I've gotten were with wood no longer than the baffle - about 13". Not what one would think for this size stove. And not what I have much of in my wood pile right. Everything is cut 14-16" for the Quad.

 

[Battenkiller]

About the VC stove: Since the stoves were chosen on the basis of the California chimneysweeps surveyed, along with the project manager, it's possible that 'updraft' and 'open' represent the ways it was most often used in that area. Back then, the downdraft mode had a reputation for being very finicky.

An altered procedure for cold start with fir was used with the Kent - the first main load was simultaneous with the kindling load. The reason is not explained.

After watching the TF burn the last couple days, I decided to line the rest of the side and back walls under the baffle. It definitely raised temps in the firebox, I could even feel more heat from the glass.

This early-stage dirty burn is made worse if the wood length is near the maximum. The flames from the forward ends have nowhere to go but directly up and out the baffle, with no chance to mix with any air, producing prodigious amounts of smoke. Not good. The best results I've gotten were with wood no longer than the baffle - about 13".

Yeah, I'm crushed that he didn't appear to burn the VC as designed, or even to name it. Maybe it was a clone of identical design, like a Scandia? I tracked the good professor down to a fancy prep school in NM and sent him an e-mail asking him about it. He either is no longer there, or he hasn't had a chance to answer... or thinks it impudent of me to contact him there regarding this matter. No word as of yet.

Seems all the test loads were much lighter than what we'd normally load our stoves with. 17.5 pounds of oak for the main loads? I put individual rounds of shagbark hickory in my stove that are almost that big. Sounds like there was plenty of room left above the charge for adequate mixing of gases and air, which might account for the higher efficiency numbers across the board than I expected. But most folks don't burn that way. They seem to load the stove to the gills to try to achieve the Holy Grail - the overnight burn. I myself am often guilty of the same thing.

BTW while some emissions were lower with the fir in the Kent tests, the crucial PM and creosote factors were actually a bit higher. Something a scientist would describe as "significant" (statistically speaking) but certainly not appearing to be substantial when looking at the charts.

The reason given for varying the way the Kent was loaded was in order to "more closely follow the testing procedure used in the Oregon-certified testing of the same stove (and hence enhancing the value of the inter-laboratory comparison of results)". I don't like that at all. If they wanted to do that, they should have made several separate runs with the different load method and shared that data with OMNI. Smells of sloppy science to me, and I'm a bit disappointed with that aspect of the tests. I'm not at all in favor of experimental design based upon expected outcome. I hope that wasn't behind this decision (we know he really liked the Kent), but like so many other things in science, we'll probably never know for sure.

Another thing to consider is the controlled draft setup (see attached photo below). Necessary, of course, in order to get repeatable results, but not representative at all of the way most folks will burn. Sluggish draft at startup, leading to excessive draft as flue temp rises during warmup, then a reduction in draft as temps stabilize during secondary combustion, then dropping to very low levels during the coaling stage. I'll be willing to bet that the guy who stuffs his stove to the burn tubes then shuts it down for the night with the primary barely open is spewing out a lot more particulate matter than his "clear" flues gases exiting the stack tell him. Cleanest burns reported in this study were during the highest burn rates - something most folks fastidiously avoid in their attempts to extract the last blessed BTU from their wood.

Most perplexing of all is how these stoves were able to burn green oak (41% MC) so cleanly and efficiently, particularly without a very substantial firebox full of burning wood to get it going. Again, Shelton describes the green oak burns as significantly less efficient (mostly because of the excess air needed, not because of reduced combustion efficiency), but looking at the charts, the green oak burns are not substantially different from the seasoned oak. Why? And perhaps the most head-scratching result of all, the fact that green oak deposited only 1/4 of the creosote (and by extension, 1/4 of the PM) as seasoned oak when burned at high burn rates in a conventional air-tight stove. This is the opposite of what has anecdotally been reported for years now. This result might be expected (and was observed) in the open stove, where the creosote is so diluted with excess air that it exits the stack before it has a chance to collect on the flue walls, but not in an air-tight design. Seems high burn rates are the key.


If everyone burned their wood at high burn rates when the air-tights first hit the scene instead of stopping them down to try to get more heat out of the wood, we probably wouldn't be stuck with all the EPA regs we have now. New product development might have proceeded along the lines of increased efficiency with reduced emissions as a side benefit, rather than the other way around.


My rudimentary knowledge of forge design tells me that by increasing the insulation and decreasing the available volume of the firebox, internal temps will get a lot higher with the same energy input. Gas forges used for hammer welding of iron need to get close to 2500ºF inside. The standard procedure is to decrease the interior space while adding an extra wrap or two of Kaowool on the outside. Gets you hotter temps with the same size burner. Yup, I'll bet you get a lot more heat out the front of that stove with the IFB. What better place to exit other than the flue?

 

[precaud]

Yeah, I'm crushed that he didn't appear to burn the VC as designed, or even to name it. Maybe it was a clone of identical design, like a Scandia?

Yes, it is a shame, and curious, that was the only stove not positively identified. But again, given that several people had input in the selection process, it's a stretch to think the exclusion was intentional. But who knows.

I tracked the good professor down to a fancy prep school in NM and sent him an e-mail asking him about it. He either is no longer there, or he hasn't had a chance to answer... or thinks it impudent of me to contact him there regarding this matter. No word as of yet.

Santa Fe Prep - high school for wealthy families. My son went there for one year (money on his mom's side of the family). It was ridiculously expensive in the 90's - can only imagine what it is now. Knowing the school, chances are it's not a full-time gig for him.

I also emailed him on Sunday, at the same email address, with questions about the emissions kit. No reply as yet.

Seems all the test loads were much lighter than what we'd normally load our stoves with. 17.5 pounds of oak for the main loads? I put individual rounds of shagbark hickory in my stove that are almost that big. Sounds like there was plenty of room left above the charge for adequate mixing of gases and air, which might account for the higher efficiency numbers across the board than I expected. But most folks don't burn that way. They seem to load the stove to the gills to try to achieve the Holy Grail - the overnight burn. I myself am often guilty of the same thing.

Yes, I think I made that point earlier - the piece sizes were small given the load weight. But then, I almost never stuff my stoves to the gills. I learned to burn smaller loads hot back in the 80's and still basically do that. But then, it's hard not to burn pinon hot. Also, our wood isn't as dense as what you have out east. As BG aptly noted, out west, we hoard hardwoods (when we can find it) and save it for the times when it's really needed. Most of the time we're cruising on softwoods. A typical load for me in the Quad (1.5 cu ft) is 10-15 lbs of pinon. Burns in 2-3 hours.

BTW while some emissions were lower with the fir in the Kent tests, the crucial PM and creosote factors were actually a bit higher. Something a scientist would describe as "significant" (statistically speaking) but certainly not appearing to be substantial when looking at the charts.

That has to do with the weighting of the Oregon averaging, which emphasizes the low burn rate results more. He discusses that in the text. In the Kent, 0.8 kg/hr is basically a smoldering burn. A truer picture is in the PM vs burn rate charts.

The reason given for varying the way the Kent was loaded was in order to "more closely follow the testing procedure used in the Oregon-certified testing of the same stove (and hence enhancing the value of the inter-laboratory comparison of results)". I don't like that at all. If they wanted to do that, they should have made several separate runs with the different load method and shared that data with OMNI. Smells of sloppy science to me, and I'm a bit disappointed with that aspect of the tests. I'm not at all in favor of experimental design based upon expected outcome. I hope that wasn't behind this decision (we know he really liked the Kent), but like so many other things in science, we'll probably never know for sure.

Agreed, I have discomfort about that part of it too. And basically what I've distilled it down to is what I've seen in using it; the Kent's emissions behavior changes dramatically after the first 20-30 minutes, especially in the first load from a cold start. It goes from looking very pre-EPA to right up there with the cleanest after that initial period. Merging the kindling phase with the first full load no doubt helped.

Another thing to consider is the controlled draft setup (see attached photo below). Necessary, of course, in order to get repeatable results, but not representative at all of the way most folks will burn. Sluggish draft at startup, leading to excessive draft as flue temp rises during warmup, then a reduction in draft as temps stabilize during secondary combustion, then dropping to very low levels during the coaling stage.

True, but I think the EPA test rigs all use controlled draft setups. One can only have so many variables floating at once - it makes total sense to me they'd tie the draft down.

I'll be willing to bet that the guy who stuffs his stove to the burn tubes then shuts it down for the night with the primary barely open is spewing out a lot more particulate matter than his "clear" flues gases exiting the stack tell him. Cleanest burns reported in this study were during the highest burn rates - something most folks fastidiously avoid in their attempts to extract the last blessed BTU from their wood.

Absolutely. Is that not true for your VC too? That's one area where EPA stoves have made big strides - clean burn at low burn rates. See notes above about the Oregon weighting.

Most perplexing of all is how these stoves were able to burn green oak (41% MC) so cleanly and efficiently, particularly without a very substantial firebox full of burning wood to get it going.

Where are you getting that from? Green oak was ONLY tested in the Blaze King and conventional stoves (open and closed), none of the others.

It's telling me I have 0 characters remaining...

 

[precaud]

And perhaps the most head-scratching result of all, the fact that green oak deposited only 1/4 of the creosote (and by extension, 1/4 of the PM) as seasoned oak when burned at high burn rates in a conventional air-tight stove. This is the opposite of what has anecdotally been reported for years now.

The only thing I can think of is, this is also a side-effect of the Oregon weighting. I can't imagine what else would do that statistically.

If everyone burned their wood at high burn rates when the air-tights first hit the scene instead of stopping them down to try to get more heat out of the wood, we probably wouldn't be stuck with all the EPA regs we have now. New product development might have proceeded along the lines of increased efficiency with reduced emissions as a side benefit, rather than the other way around.

Perhaps. But many felt (and still feel) the same way about digital audio - saying audio wasn't "ready" for digital. I disagree. BTW, take a look at the Xeoos Twinfire - it's hitting high marks on both sides of the equation.

My rudimentary knowledge of forge design tells me that by increasing the insulation and decreasing the available volume of the firebox, internal temps will get a lot higher with the same energy input. Gas forges used for hammer welding of iron need to get close to 2500ºF inside. The standard procedure is to decrease the interior space while adding an extra wrap or two of Kaowool on the outside. Gets you hotter temps with the same size burner. Yup, I'll bet you get a lot more heat out the front of that stove with the IFB. What better place to exit other than the flu?

Yup. And all exposed metal in the firebox burns so clean you could eat off of it. But if you're going to super-insulate the firebox, the load gassifies more quickly and the secondary air system has to be substantial to handle it. That's the way the new generation of Euro stoves are going - highly insulated fireboxes with robust secondary air systems burning small loads hot and fast. No attempt to prolong the burn - instead, lots of post-secondary heat exchanger surface area (Twinfire) or lots of thermal mass (thick Skamol liners).

And this points to one thing that I want to explore further; the impact of "excess air" on efficiency. One thing is clear to me - EPA stoves burn clean in part because there is a large amount of excess of air available at all times. Sheldon shows pretty emphatically that overall efficiency is lowest on the two appliances that have the highest air-to-fuel ratio - pellets and open stove. I'd like to see similar figures on some EPA stoves. I bet it's a big deal, and that the efficiency numbers being published by marketing departments are fudged to the hilt to hide it. I bet your VC scores very well in that department - very little excess air inside. If Sheldon's right, that is a major differentiator in the overall efficiency score between stoves.

 

[Battenkiller]

]Most perplexing of all is how these stoves were able to burn green oak (41% MC) so cleanly and efficiently, particularly without a very substantial firebox full of burning wood to get it going.

Where are you getting that from? Green oak was ONLY tested in the Blaze King and conventional stoves (open and closed), none of the others.

Right. I was thinking I had already posted a graph that showed the stoves that burned green oak, but that was in another thread. Still, both stoves did admirably with the green when given enough air. The VC may not have fared quite so well if they burned it with the bypass closed. Might not get enough air (although my Vigilant handles it without indigestion). But that doesn't explain the spectacular results with the Blaze King. Less than 5 points drop in overall efficiency? Who'da thunk?

I know you love the physical solutions, but you gotta respect the power of a catalytic combustor used wisely. Maybe it's the frustrated boy chemist in me, but knowing how catalysts work makes me feel they should still have some place in future stoves, even if just as an adjunct to the high-technology burn profiles of the newest designs.

 

[precaud]

Right. I was thinking I had already posted a graph that showed the stoves that burned green oak, but that was in another thread. Still, both stoves did admirably with the green when given enough air. The VC may not have fared quite so well if they burned it with the bypass closed. Might not get enough air (although my Vigilant handles it without indigestion). But that doesn't explain the spectacular results with the Blaze King. Less than 5 points drop in overall efficiency? Who'da thunk?

Two thoughts: First, see note in "wet wood" thread about the burn cycle. Long time spent in the charcoal phase, where all stoves perform about the same. Second, lower PM with green oak in the closed VC test says to me there was TONS of air pouring through that sucker in order to get it to burn. That is confirmed by the air-to-fuel ratio chart. Lots of dilution going on.

I know you love the physical solutions, but you gotta respect the power of a catalytic combustor used wisely. Maybe it's the frustrated boy chemist in me, but knowing how catalysts work makes me feel they should still have some place in future stoves, even if just as an adjunct to the high-technology burn profiles of the newest designs.

They do and they probably will. But yes, you're right, I prefer other solutions, if for no other reason than the challenge to discover them and make them work. Add in to that a basic discomfort about the sourcing of the elements used in catalysts.

 

[Battenkiller]

Two thoughts: First, see note in "wet wood" thread about the burn cycle. Long time spent in the charcoal phase, where all stoves perform about the same. Second, lower PM with green oak in the closed VC test says to me there was TONS of air pouring through that sucker in order to get it to burn. That is confirmed by the air-to-fuel ratio chart. Lots of dilution going on.

I'll go back to the green wood thing again only because of what your comments imply about the test results, but I don't want to continue to hash this out here on your thread about the Kent stove itself. Maybe on another thread...?


Yes, the green wood needed more air to achieve maximum burn rates, he even says so in the text. However, the overall efficiency numbers don't lie. There was not a significant loss of sensible heat up the flue due to the extra air being introduced. Yes, some dilution effect is evident, especially is the open stove, but that doesn't support anecdotal evidence of massive amounts of creosote deposition in residential chimneys venting stoves burning green wood. Just the opposite is reported here, and the dilution effect is clearly aiding this... to the benefit of green burners everywhere.

If you examine the air:fuel ratios, there was not a significant amount more air actually needed to burn the green oak in either stove tested with it. Even at a burn rate as low as 0.7 kg/hr, the conventional air-tight was using less air burning green oak than the Lopi used burning the dry fir test load. Except for a few outliers, the data set shows that the Blaze King used almost an identical amount of air at all burn rates with either the green or the seasoned oak. Which, as I mentioned above, is reflected in the overall efficiency numbers.

Similarly, if massive amounts of PM were exiting the flue unburned, this would have been reflected in both the combustion efficiency and overall efficiency numbers, and this is clearly not the case. Besides, the sensors and filters catch all of the emissions, so dilution wouldn't affect either the g/hr or g/kg numbers.

One last thing to say is that, although it was called "green" oak in the report, that doesn't mean it was fresh-cut. Newly harvested oak generally has a MC of about 80%, not the 41% stuff they used in the tests. And 41% dry-basis is not 41% water by weight, it is 29% water by weight. That's only 9% more water per pound of wood than the "seasoned" stuff. I find it frustrating that, even in a scientifically controlled study, the author included both ways of expressing moisture content in different places within the same report. No wonder everybody gets confused about this essential bit of information.

And that's all I have to say here about burning green wood.


Considering the stated +/-25% uncertainty in the Oregon weighted averages, the only really significant fuel factors across all the tests and burn cycles was for the production of elemental carbon (soot), and NOx production (assumed... based solely the performance of the Blaze King - a catalytic stove commonly thought to produce high NOx anyway). The major contributing factor in this study was the appliance effect. The better stoves burned both cleaner and more efficiently regardless of the fuel type - green oak, seasoned oak, or doug fir. Seeing as how that was what was being investigated to begin with, we have a clear winner:


The stove is much more important than the quality of the wood... at least in this study.

Add in to that a basic discomfort about the sourcing of the elements used in catalysts.

I hear you, mate, but we are pretty much stuck using precious metals as long as the population continues to increase and the technology necessary to reduce our contribution to pollution lags behind. The fact is that catalysts are a crude but highly effective club that can be applied after the fact to cleanup the mess left behind from inferior design. As long as financial motives are the driving force behind scientific development, industry will continue to use whatever crude and inelegant solution they come up with providing that it satisfies the bottom line. The nice thing about the metals themselves is that they are recoverable once the appliance craps the bed. The combustors and converters themselves decline in efficacy with use, but the metals themselves can be largely recovered during recycling of the spent devices.

Anyway, keep working on your projects, they may lead to the next breakthrough in this technology. Me... I'm more of a thinker than an inventor. I like to know how things work, but leave it to the smarter guys to figure out how to make them work better.

 

[precaud]

I'll go back to the green wood thing again only because of what your comments imply about the test results, but I don't want to continue to hash this out here on your thread about the Kent stove itself. Maybe on another thread...?

Good idea. I'll have to wait until later to reply to the rest, I don't have the Sheldon paper on this computer to refer to.