VC 2n1 running non-cat vs with cat

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arnermd

Minister of Fire
May 16, 2014
541
Tolland, CT
Have you tried burning without the CAT? I have my stove somewhat dialed in but not always. I was concerned with destroying my cat, and relegated it to my lower burns when I did see the value of doing so. But removed as I left shoulder season but tried from time to time to determine if it better for overnight burns. This is a controversial subject. :) but I can only go by my experience. I inquired with two stores about this, one is a well known dedicated shop that carries a wide variety of stoves and another sells stoves as a means to an end on top of all the other stuff they sell. Both seemed to suggest you would leave the cat in all season. But when I would show them the brochure from VC's website that shows efficiency goes down as you burn hotter, there was no explanation. VC didnt reply. I dont think this will change the temperatures much in your secondary, but maybe it will as those gases arent being combusted as easily. I do not get the jet blast sounds that others get, but I do recall once getting it with the cat installed during a hotter fire. So who knows, give it a shot.
Below is the screenshot from VC's website that shows efficiency actually goes down as the stove burns hotter. Sorry the imagine stinks, but this is what they have on their website. Notice that anything beyond a minimal burn and you are just wasting the use of a catalyst if efficiency is anything you care about, which for me it is one of the most important things, only second to safety. I did not notice much less smoke with the cat installed once I had a warm stove. What's interesting is, there is no mention of what a minimum burn would be. Because there is a minimum to which the cat actually operates. And once you are there, your stove is burning pretty hot. So to me, that would mean the window for using the cat is so minimal unless you get it to operate catalyst range, and work to keep it there.
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I have run without the cat and as best I can recall there was not a huge difference in performance. Secondary temps were lower but still can be pretty hot (>1100 as I recall) but it took a lot longer to get there and required a healthy primary burn. I believe all the larger VC stoves (Defiants, Encores,) were designed for secondary combustion (cat or non cat). The cat just gets you lower temp secondary light off and more complete combustion.

I don't claim to be an expert but the shape of the curves makes sense to me, efficiency is a function of flue gas temp and unburned fuel in the exhaust.

With a non cat stove:
  • low firing rate a larger amount of unburned fuel is going up the stack = Low eff
  • As firing rate increases more complete combustion occurs = better eff
  • At some point you get complete combustion but stack temps are high so a larger amount of heat goes up the stack = declining eff.
With a Cat stove:
  • Low firing rate still produces complete combustion (because of the cat) and exhaust temp is low (due to low velocity of exhaust gas, has resonance time to transfer heat to the house)
  • As firing rate increase you still have complete combustion but gas velocity is increasing and less resonance time for heat exchange (more heat goes up the stack) = declining eff.
So why do I run with a cat:
  • I am predominantly concerned with creosote build up in my stack. I clean once a year and do not want to get on the roof midwinter to do it again.... I need to make some mods to my stack so I can clean from bottom.... On the to do list.
  • I am not too concerned with efficiency provided I get 8 hour burns, minimum. Lugging less wood around is preferable but not critical. Being able to run clean at low firing rates is nice in the shoulder seasons for sure.
 
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Reactions: a59cheffy
Yet another posting extracted from the bucket thread. Informative posts like this get buried there.
It's a very helpful observation and often sought information. Please save the bucket thread for chit chat about trivia and snowboards.