We didn't discuss increasing secondary air. I asked some questions around it here and theere but they were never addressed head on.
I suspect if I was able to increase the size of the secondary intake (or the primary for that matter), I still wouldn't have enough draft to pull through the volume of air I need to get the o2 I need.
Andy
Thanks for the answer. I get the reluctance to change the calibration of the stove thing - they can't. Unfortunately, that's the same thinking (though, yes, required by law), gets me a snowblower that runs so rich at this altitude, I can't use it without getting ill on a calm day. It also gets me a (insert modern 2 stroke powered item here) that won't work until I find some way to remove the screw limiters, and lean it out.
Andy - I'm sure this doesn't help you, but since it's related, and sometimes somebody shows me where my thinking is wrong, here goes(!):
I'm going to jump into theory - at least as I've come to understand it: In a cat stove, there's two combustion chambers. The same is true on a tube stove, really. With a cat, theres's the firebox, and the cat. With a tube stove, there's the lower section with the wood and coals, and the upper section with the air tubes, under the insulation.
It's pretty easily seen on a tube stove with a window. You can increase the primary air under some circumstances, and the lower fire perks up, while the fire along the top dies out. The fuel is being consumed on the lower level. Conversely, if the air supply is reduced, under certain circumstances, the lower fire loses visible flame, but the top of the stove lights off. The fuel is allowed to exist long enough to get to the top by the limited air on the bottom, and combined with adequate air at the top, it ignites.
The cat stoves I've seen, aren't designed for efficient combustion in the firebox. The firebox provides smoke for the cat to burn. If the door is opened, an unusual quantity of air is provided to the firebox, and if conditions are right, that's going to improve firebox combustion and reduce the amount of smoke the cat has to deal with. That's why they are typically supposed to start up with the door open, it's a cleaner burn that way if the cat is too cold to work, and it helps to heat the chimney. Once the stove is running in its normal mode, with the door closed, the primary air becomes a smoke feeder control for the cat. More primary air, more smoke to burn, less air, less smoke.
Within reasonable limits for the size of the cat, as long as there's enough air available for the cat (or tubes - in a tube stove) to burn the smoke provided to it, things go well. Not enough air to combine with the amount of smoke provided, and some will go up the chimney unburned as smoke. Same with the snowblower. Big, fixed, sea level, carb jet, not enough air available to mix with the fuel provided, and a lot of CO and other issues result.
So, here's why I went through that step by step: My cat stove that's been burning all day, is still smoking some outside. Sometimes it doesn't, but today it is (low draft day). The cat is at 1,200, and it probably doesn't have 10 day-long burns on it. I left the primary at 90% shut on the last reload, and I just reduced it to say 92% shut (since it's still smoking outside), which is a quarter turn each on the air control knobs (a "smidge"). Earlier today, I did a half turn, and it lost enough draft to start smelling in the house. -- The big difference between the snowblower and the stove, is the snowblower has a positive displacement engine. Every revolution pulls in a set volume of air. If it doesn't burn to its potential, I get less power, and more emissions, but it keeps running. The stove is not positive displacement. If it doesn't burn to its potential, you either get more smoke by using the primary air to keep it pumping (which was my only solution for years), with the primary open enough that there's enough hot gas flow up a masonry chimney to sustain the draft, though there's not enough secondary air to burn all of the fuel that the primary is providing - so it runs but smokes. The other alternative is to reduce the primary to the amount of fuel the secondary is able to burn, but then there's not enough energy in the form of a volume of heated products of combustion to keep the chimney hot to sustain the draft, starting a cascade that ends with the smoke in the house, and the fire dying out. Yes, there may be a happy medium, but it's an incredibly fine line to walk, especially when it changes with stage of the burn cycle, wind, temperature, and whatever else.
30 minutes later - After adjusting the primary knobs 1/4 turn closed, the cat is at about 1,100, and the smoking has stopped, If I had nothing better to do than to look at the chimney, and adjust the stove a "smidge" every half hour, this would be a solution.
So, that's my current theory. My stove is limited by the amount of fuel it can burn based on the secondary combustion air available at this altitude. Unfortunately, it's often too little for the masonry chimney to stay hot enough. If I run enough gasses up the chimney to keep it drawing adequately, the cat can't burn it all, resulting in smoke.
i'm going to get in trouble with somebody, but I don't actually care about the smoke. It'll be fertilizer stuck to a snowflake before it gets the chance to bother anybody else. I would like to burn it for heat, though. I'd also really, really, like it if it burned in the stove instead of creating crud I have to clean out of the chimney!
So, I'm really liking the idea of trying the increased and adjustable secondary air idea I posted above. I think it might just widen the workable combustion range of my stove to get it to work reasonably with my chimney setup.
