I am with you on this. But…..this is a discussion forum and educational forum. OP asked and we are sharing experiences.
Smoke with cat engaged - Chinook
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Ashful
Minister of Fire
Oh, totally agreed. That's why I started with my opening sentence.
But I wanted to also assure the OP that this is nothing over which they need to really fret or lose any sleep. A clean chimney at the end of the season is all that matters, unless you're living in an inversion zone or some place with smoke ordinances. Even when mine "smokes", it's a faint whisp that disappears within 18" of the cap... not even sure if it's smoke or steam most of the time.
I'm thankful for all of the experiences shared. It matters for me not just as curiosity but for my air quality. When there's significant smoke it does not dissipate in 18" of the cap - I can see a trail of smoke sometimes 40 or 50 feet long, and usually within 15 minutes I can start to smell it in the house. If I can smell it, I'm sure there's particulates coming into the house. Finding a way to seal the house better might help, but so does generating less smoke. Adjusting the t-stat in increments has paid dividends already.
Ashful
Minister of Fire
Understood. Always good to aim to reduce smoke, pollution, all that. But also, providing an outside air inlet to an outside air kit (OAK) would likely resolve this particular issue, as it removes the net draw on the house created by the stove.
Right, I don’t mean to speak poorly of our beloved BKs but they are not smoke free. It becomes especially apparent when burning a noncat stove at the same time and it really being smoke free. The new BK operator should not be surprised if they see emissions during the burn.
Smoke getting back into the house is not pleasant. Why would that happen? Close the windows. Even when my BK smokes during the long burn it is not excessive and either rises or blows away.
Interesting. The chimney is in the south east corner of the house. The prevailing winds come from there, blow the smoke over the house, and then it tends to drop down beyond the north-west corner where the entry door is. Your idea is that if the house is in negative pressure, its sucking that smoke in somewhere?
I don't have an OAK but I could easily open a window closer to the stove and away from where the smoke is blowing and see if that keeps smoke from creeping in. The house is not super tight in any case (basement door lets in a steady slight draft) but I will try next time.
Now that I have a BK I can actually keep the windows closed since my stove is not overheating my house! I think small particulates can still get in somehow - air does, after all, and 2.5 microns is pretty tiny.
During a long burn, especially 2nd half, so far, its been pretty smokeless. The first hour or so, especially when I opened the t-stat from closed to WOT, can generate a lot of smoke - way more than I was expecting from the literature. The Jotul F3 I had was listed at 4 grams per hour of particulate emission, the BK at 0.7 - a 6 fold improvement - and so far I don't really see that. Of course, I'm not up on the roof measuring it either and the Jotul has gone to a new home anyways.
Today was warmer, and I loaded only half-full in the morning. That also seemed to reduce smoking after loading and the house stayed around 74F even with a sunny day around 40F.
An important point is the emissions rating may not be a measurement of the visible smoke. Like it’s grams per hour of “stuff” and the stuff you see may be weightless condensed volatiles. Some steam, some raw fuel, and some particles.
The whole testing method may not have any basis in reality either. It’s like epa miles per gallon figures for your truck.
They’re all rated very clean these days and all pretty similar yet visible emissions obviously vary a lot. I do care about visible emissions more than the gph rating on the label. I want to burn in stealth and not bother anybody with it.
Ashful
Minister of Fire
There are certain days when smoke from the chimney on one end of my house gets blown across and drawn into the other end of the house. I may not be able to see the smoke more than 18 inches off the top of my pipe, but I can occasionally smell it coming into the house, on certain days with certain wind conditions.
Hey, all of us without an OAK are drawing outside air into the house to feed the monster, the same air we're polluting with our stoves, to varying degrees. No surprise that some, but hopefully miniscule and very diluted portion of that is smoke that you can smell or measure for particulate pollution.
Of course, that tiny bit of wood smoke particulates may not be the worst pollutant in that air, depending on where you live!
So I've got a theory:
It's often talked about how new cats are "overactive" pegging the temperature probe at the end of the active zone. After a while this settles down and the cat runs at more "normal" temps. To cause this change a new cat would have to be combusting more of the wood gases to cause the higher temps, therefore a "broke in" cat is passing some amount of combustible gases through it without completely oxidizing them. What these gases is are is the mystery, is it CO? CH4 is particularly difficult to oxidize completely in most catalytic converters, or is it a host of compounds some of which cause the appearance of smoke at the cap and the typical wood smoke smell.
Is there a way to keep a cat from going overactive (which per my theory) also erodes and flattens the washcoat on the cat substrate leading to decreased converter performance? Can more air be added before the cat as dilution air to limit temps, prolong the life of the cat, and clean up emissions while doing so? Could such a system be mechanically controlled, although likely not responsive enough. Electronic controls could do the work with a simple thermocouple based feedback loop.
Ah ha, I've finally found a reason to add electronic controls to the beloved bimetallic coil controlled BK stove!
It's often talked about how new cats are "overactive" pegging the temperature probe at the end of the active zone. After a while this settles down and the cat runs at more "normal" temps. To cause this change a new cat would have to be combusting more of the wood gases to cause the higher temps, therefore a "broke in" cat is passing some amount of combustible gases through it without completely oxidizing them. What these gases is are is the mystery, is it CO? CH4 is particularly difficult to oxidize completely in most catalytic converters, or is it a host of compounds some of which cause the appearance of smoke at the cap and the typical wood smoke smell.
Is there a way to keep a cat from going overactive (which per my theory) also erodes and flattens the washcoat on the cat substrate leading to decreased converter performance? Can more air be added before the cat as dilution air to limit temps, prolong the life of the cat, and clean up emissions while doing so? Could such a system be mechanically controlled, although likely not responsive enough. Electronic controls could do the work with a simple thermocouple based feedback loop.
Ah ha, I've finally found a reason to add electronic controls to the beloved bimetallic coil controlled BK stove!
Yes ,I think you are describing things that may be correct. (Minus the electronics, lol).
Though BK says testing showed cats were still performing within EPA standards of emissions after 9 years (I believe).
I also note that my DutchWest FA had precisely that, mechanically controlled preheated air coming in just below the cat.
Though BK says testing showed cats were still performing within EPA standards of emissions after 9 years (I believe).
I also note that my DutchWest FA had precisely that, mechanically controlled preheated air coming in just below the cat.
Ashful
Minister of Fire
Not an answer to ABMax's questions, but on a related note, I believe BKVP said their testing is all done on an "aged" combustor. The EPA requires a certain number of hours on the combustors used in the stoves under test, if I recall correctly.
But I have also wondered what could be done to avoid pegging temps during this initial hyper-active stage. You would assume it would have to improve cat life even more than they have already achieved.
Having run some cat stoves from the early 1990's, I can tell you BK and Woodstock have come a long way, from where the state of the art was back then. My old Jotuls would simply devour combustors, and while bholler will tell you it's the worst stove Jotul ever made, many others will claim it's among the best cat stoves of its day. Both could be true, if i.e. all cat stoves of that day pretty much sucked.
But I have also wondered what could be done to avoid pegging temps during this initial hyper-active stage. You would assume it would have to improve cat life even more than they have already achieved.
Having run some cat stoves from the early 1990's, I can tell you BK and Woodstock have come a long way, from where the state of the art was back then. My old Jotuls would simply devour combustors, and while bholler will tell you it's the worst stove Jotul ever made, many others will claim it's among the best cat stoves of its day. Both could be true, if i.e. all cat stoves of that day pretty much sucked.
I had an old (previous owner) cat in the DutchWest. Given theshape of the stove I don't think they ever replaced it. It was still good. I did like how it burned. User control was quite good. (No Tstat tho.)
That was a 1983 vintage. I think that design was pretty good.
That was a 1983 vintage. I think that design was pretty good.
Ashful
Minister of Fire
You may have benefitted from that older combustor. My one Jotul that still had a 20 year old OEM cat actually behaved pretty well, too. But two others were purchased with ruined cats, and each new combustor I put into them went ultra-nuclear, to the point of self-destruction. Even a new cat in the stove that was well-behaved on the original went to 2400F self-destruction.
This kind a sounds like a hybrid stove design. I know the Jotul F500 V3 cat has a 20 year warranty. We’ll see in how these hybrid stoves cats do in a few years. I think most hybrid designs use the cat as a final clean up and not the bulk secondary burn such as BK.
Not sure on the BK but looking at my stoves EPA test report it stated stove was run for 50+ hours prior to testing.
I think the only difference in those cases is the design of the heat shedding off of the cat
Today I opened a window close to the stove a crack when reloading. A warm day (high of 42F) again so a half load. A half load sure seems to generate much less than half the smoke. In any case, with the window open a crack, the smoke did not enter the house, which I'll call a win. My theory is that when exiting the chimney the smoke is warm, thus rises, and is unlikely to fall straight back down and get dragged into the open window.
I wonder if a cat can be a little out of alignment and pass more smoke. I didn't see the installers check the cat positioning after it's hour-long ride on the back of a truck. I assumed at the time the cat would be bolted in place such that it couldn't move, but it is possible it's sitting catty (pun intended) corner and when there's extra smoke such as a full load it's leaking as it were?
Ashful
Minister of Fire
Not likely. The combustor is wrapped in 30" of 2" x 1/16" interam gasket, which expands and essentially jams it into place once fired. The hole it slides into is only maybe 3/16" to 1/4" larger than the combustor itself, the gasket easily swells to fill the entire hole.
And yes, the smoke does go up, but one part of my house is two stories taller than the other, and that's the vector for smoke getting drawn in. Essentially, a 50 ft. high building nextdoor to a 15 ft. high chimney.
And yes, the smoke does go up, but one part of my house is two stories taller than the other, and that's the vector for smoke getting drawn in. Essentially, a 50 ft. high building nextdoor to a 15 ft. high chimney.
Interesting,
Any idea who installs the cats on stove delivery? Dealer or the cat comes installed from BK. @BKVP ?
Ashful
Minister of Fire
I think the combustors of my stoves were sitting in the bottom of the firebox at delivery. Been a few years, but I seem to remember it being pre-wrapped with gasket and tape, but not installed.
BKVP
Minister of Fire
Installed at factory. Make certain bypass is locked down, not just closed.
Some smoke does appear randomly. Mostly upon refueling and initial startup.
BKVP
Minister of Fire
Hmm. No wood heater tested with a catalytic combustor has ever left our facilities without the combustor installed and twine secured with flame shield in place. It's a requirement of law they be shipped as tested. This applies to all wood heaters.
Ashful
Minister of Fire
As I said, my memory on the combustors wasn't certain, but I can say with 100% confidence that my flame shields were removed prior to transport to my house. The guys delivering them even scratched their heads a few minutes, and so I cab clearly recall we conversed on it awhile, when I asked them which direction that flame shield should face when re-installed. They made some comment about the guy loading the stoves onto the truck being worried about it falling out and causing damage in the truck ride over, so I will believe you if you say they removed it at the store.
If I recall, I believe my pair of Ashfords were the very first BK 30's ever ordered by those guys in Kintersville. I remember them oogling the stoves, and being really impressed with them, actually seeming to be happy I gave them a chance to see their first pair of them. So, it's possible they removed these bits either out of an abundance of caution, or simple curiosity.
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