Cleaning up an old smoke dragon and making it more efficient

I already put a link to the page below in a reply I had in another thread, but thought I'd give it a thread of it's own (so sorry for the repeat for anyone who's already seen this),

I bought our current stove back in 1981 from a local dealer. The brand (Wood Saver) I've never seen before or since, but bought it based on the bullet proof construction, great welds, heavy cast iron door, firebrick lining and large (around 3.6 cu ft) fire box. It was made by a small fabricator in New York's Hudson Valley. It has heated our house since, and still looks about the same today as it did when brand new.

Fast forward to a couple of years ago. The stove certainly didn't owe me anything, and I was wondering if replacing it with something more efficient might be worth doing. Since I wasn't convinced that a newer stove would really save me much wood, I did a little experiment by adding secondary burn tubes to the stove. One thing led to another, and I also retrofitted it with a cat this year. Gary Reysa of Build it Solar was nice enough to put the story up on his site. Besides the retrofit projects, I also put some info in about how I did the performance testing of the stove . The link to the page is below. I am now a firm believer that all this new burn technology works and saves fuel, but now have my stove efficient enough and clean enough I doubt I'll be replacing it anytime soon. It's not the nice looking stove you'd want in a living room installation (especially with the cat box on it) but for my cellar installation it's fine and I'm currently warming my house with long slow burns (typical of a cat stove) with no smoke out of the chimney once I engage the cat.

http://www.builditsolar.com/Projects/BioFuel/CatRetrofit/CatRetrofit.htm

Scott

Wow, looks like you cleaned that old stove up quite a bit. While I'm not too keen on drilling holes for a secondary air setup, I've often thought about the retrofit CAT units that are out there. The only thing that's held me up is that I was under the impression that the after market setups did not work so well because there was no additional air supplied to the CAT to help the smoke burn. Does your CAT box introduce additional air to the combustor or is it "air tiight" except for the flu gas?
If your unit works fine without additional air being supplied to the combustor, I may revisit the idea of an after market CAT.

That's where doing the secondary air first, made things easy. The secondary air tubes also supply the preheated air needed for the cat. The cat box is air tight. I'm finding, during the shoulder season, that things work best for a slow burn if I close off my secondaries about half way, and close the primary drafts way down. I'm able to get 12-14 hour slow burns this way (with a mostly full load of wood, stove top temps 300-400 degrees and cat box temps 400-500 degrees), and the cat stays active almost all the way through. When I need more heat, I just play with the controls to get the best combination of secondary burn and cat burn, but have to pay attention to not overheating the catalyst at the beginning of the burn.

I'm not sure how well the aftermarket ones work. Maybe someone, who has tried one, might reply. What I didn't like about the ones available, was they are up away from the stove more than the one I made, they are most likely using a 1" high ceramic catalyst where I was able to use a 2"high steel catalyst (which lights off at lower temps), and due to my relatively short stove pipe, I wanted something that would be more likely to send the heat from the catalyst out into the room instead of up the flue.

I read the write up on BIS, Nice job, I am considering a similar mod to my Fisher. It is already modified with secondary burn tubes and SST baffle. I am thinking about adding a cat or 2 above the baffle , like on the BK stoves.

I like your burn tube job better than mine...very professional looking. The cat should work even better in the stove. I was originally thinking of doing the same. I just couldn't come up with what I thought would be a leak free penetration for the bypass damper, so I went with an add on unit. One other thing I should mention is that cats don't like galvanized coatings, so I used stainless steel fasteners in mine (the stainless on stainless will end up galling and seizing due to the heat, though). All except the damper rod...that's just standard threaded rod. I bead blasted the zinc coating off of it before I installed it.

Scott: hope you dont mind me resurrecting this old thread but I want to comment that I was thinking of trying to do this very thing with my Englander 30NC. It already has the 2ndary tubes and I would just add the combustor on top. You implementation is very impressive. I wish a major manufacturer would take notice and develop a refined design for mass production. A coil thermostat to control primary intake would solve the over fire problem so as to avoid the need for babysitting.

I will be playing around with this idea this summer while my stove is offline. Thanks for doing a lot of the groundbreaking for the rest of us DYI'ers

Hi Scott,
Just checked out that web page on the stove upgrade and I can tell you that Sud Chemie does indeed make the SS cat for Condar.. Both VCBurner and I bought one on E-bay for the paltry price of $59.00 shipped.. I called Sud Chemie and was told by the Sud Chemie rep that they make them for Condar and no longer sell them direct to the consumer.. One thing I wonder is how does your cat bypass damper make an airtight seal when closed? I see no evidence of any gasketing mat'l. for the damper and I doubt a metal to metal seal would work correctly.. The problem is without this seal the smoke would follow the path of least resistance and get around the damper.. Yes some smoke will pass through the combustor but to maximise heat throughput and efficiency all the smoke needs to go through the combustor.. If a good seal is not made that little bit of untreated smoke will lead to creosote formation.. I ran into this problem this year when my bypass gasket failed.. Great job on the upgrade on a well built stove!

Ray

Not sure how much you could hope to improve an EPA stove. Those stoves are designed to run more open than the cat stoves, from what I can tell, so I'm not sure you could really turn them down to a very slow burn, can you? It'll be interesting to see the results.

59 bucks... for the steel cats? I'd have bought 3 or 4 at that price! The seal is not air tight, though the damper closes against a piece of angle iron on both sides when it closes, and unless it warps, it's a very tight fit. There's less than a 1/32" clearance on either side, though. I wondered if that would be a problem and figured that I could add gaskets at a later date if needed. When you figure the amount of clearance where leakage could occur vs the amount of area for the cat to flow through, it's minuscule. Also the heat from a lit cat should accelerate the flow through it...my theory, at least, so a little leakage shouldn't matter much. One thing that has totally surprised me, though, is that with the bypass open completely, the cat lights off on it's own and runs 800-1100 degrees on a new fire before I close the damper. So that tells me that a little bit of leakage doesn't pull any more away from the cat than whatever manages to leak through. So if a person really cared to actually shut the cat down, they'd have to put a damper under it also. I don't really see any point in that, though, as the cat can just clean up the exhaust some and contribute to the heat even before you're ready to engage it. Even on a hot reload, the temperature doesn't come down quickly, so I doubt it's getting a huge thermal shock. I try to minimize reloads when the cat's cranking and do other things to bring the temperature down 1st.

Scott

I looked on Ebay and didn't see much in the way of good deals. I did find this website:
http://catcombustor.mybisi.com/
They have a 2" X 7" on sale for $49 ea. I will probably get 2 of these and adapt them to my Fisher stove.

I have the design just about all done, the cats will go in a stainless steel bracket located above the baffle, similar to the Blaze King design.

On a different note, in the pic of my stove mod you can see white kaowool covering the baffle. I had wrapped the baffle with a 1/2" of kaowool insulation. I needed to take some measurement for the cat design so I removed the kaowool. I tried burning the stove without it, what a difference, it ran much better. Less smoke, more heat, faster heat up. Somewhat counter intuitive.

You get what you pay for, I'm afraid. These are only 1" thick so they won't have the performance of the 2" thick catalysts. Look at the chart at the bottom of the page here:

http://www.sud-chemie.com/scmcms/web/page_en_7529.htm

I believe these would be similar to what they're calling the "Envicat 3041", a budget combustor. I would be worried especially in an in-stove install of the statement about damage from potassium at temps over 1350, You will easily hit those temps with your catalyst installed in the stove. Also note the differences in combustion efficiency between the 3 types. You would probably be better off spending more money for a better catalyst.

My 2 cents,
Scott

Better heat transfer to the tubes?? Better heat transfer from the tubes and baffle to the stove top??

Scott

Hi Wes,
I remember reading that these cats work OK at 1st but can get clogged and are nearly impossible to clean due to the way they are made.. All the other cats I have seen are on the idea of a honeycomb so they can be vacuumed.. Just something to think about.. I am wondering why you need 2 cats and also why 7".. You can buy a 6"x2" ceramic cat for about $100.00 or get a Condar 6"x2" SteelCat for $125.00 from Woodstock an even better deal..

Ray

The 6" round I'm seeing on their site looks like ceramic, but they have a couple of different rectangular steelcat sizes for $125.

http://store.woodstove.com/xcart/home.php?cat=265

Scott

I looked at the replacement cat info and stoves that use 2" X 6" or 2" X 7" size cats use 2 of them.
Good point about cleaning the one I was looking at. It is made of ceramic foam.

Looks like http://www.northlineexpress.com/category/catalytic-combustors.asp has some cats on sale for a reasonable price. Just need to decide which one.

this may be a dumb question, but when do you know if its time to open or close the valve to the secondary burn tubes ?

I found it works best if I shut them down half way when I close the bypass damper to engage the cat. The cat doesn't overheat if I do this. Then I just set the primary drafts where I want them, and can leave things alone from there. I usually get the stove top up to at least 300-400 degrees before I do this. By then the cat is already running 700-1000 degrees on it's own (with the bypass open). Usually takes between 10 and 25 minutes to get to this point, on a new fire, depending on how cold the stove is. I open them up all the way again, when I start a new fire. All found out by trial and error.

Scott

hey scott

just curious. if you leave your valves wide open you'll overheat your cat right? but if you add less air the cat runs cooler, does it mean that it starts getting smokey?

2nd question. and the answer might be time will tell. if you have secondary burn tubes then the cat, will running the combo tubes and cat make your cat last longer?

Hi Frank,

Yes, but it's kind of a balancing act. The more smoke, the hotter the cat gets, cause it has more fuel to burn. The more air, the more flow, and the hotter the cat gets, most likely for the same reason, I guess. To get the stove to run hotter, I can open up the primaries more. get the fire to burn less smoky, and hot enough for the secondaries to work well, so even though the stove is hotter, the cat doesn't have to do as much and still stays within a reasonable range. As far as your second question, I have no idea...time will tell. I can say that the cat stays active enough and hot enough that I doubt I'll have trouble with it plugging up. It's also located up out of the stove and away from the flames, so it shouldn't get damaged by direct flames. I plan on taking things apart after the burning season to see what it looks like.

Scott

hi scott

here is something to think about. been thinking of what you said being a balancing act. how about those pipes going into a air box say under the stove with a bimetallic spring somewhere to feel how hot the cat is running to open and close the air. got that on my defiant for primary air.

just thinkin :gulp:

Yea, that'd be just the ticket, but I'm not smart enough to pull that one off. Kind of like the thermostatic control on the blaze kings, you'd be able to get even more control and incredibly long burns. But then, there has to be something to differentiate my cobbed up add-on from a stove designed from the ground up to do this.

Scott

if you keep up the designing and perfecting i think you have your first million there bad thing is you can't put smith on the stove, someone might mistake it for the boiler company.