Cat vs Non-cat

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Beno, Mar 6, 2007.

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  1. mikeathens

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    OK...my calculation made my head hurt. Looking back at it, I know I have to look at total wood usage vs. heat loss up the chimney to get an accurate number. Don't tell me about it, I already know. Why doesn't someone finish it, like this:

    55,000 Btu/hr for 24/7, 30 days is about 2 cords of green ash/month (not unreasonable).

    For the non cat, if you're looking at above calcs for losses, you are looking at 2.05 cord/month vs. 2.037 cord/month for the cat stove.

    OK, somebody fix this. I'm in over my head...I'm not a fuel engineer. I haven't looked at crap like this for over 12 years since my undergrad work...I come up with something like 187 lb of green ash extra burned in a non-cat stove. I know this can't be right though. should come up to more like 3000 lb....
     
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  2. elkimmeg

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    Mike it can't be figured out accurately, Call it the wife factor first year with the cat Encore replacing a 3 year old Resolute Acclaim, I don't know if I used less wood?

    Last year I worked that Acclaim all the time and it had a hard time keeping up below 15 degrees. The furnace kicked in temp set at 67
    this year the furnace zone valve has been m dissconnected and no furnace,, so my average temps have exceeded 67 possibly 69 degrees average
    69 degreees is much more pleasing to the wife. I probably used more wood with the cat stove but it gave me a longer more productive heat range partly due to more heat capacity
    18% more. I also probably used my second stove more..

    What about this formular if the same two size stoves one cat and one non cat are used and there tested effeciencies and 10% different than,
    I suspect the more effecient one uses 10% less wood. Now if the cat combustor increases the output BTUs, over equal size fireboxes, I don't know how to factor that in for
    wood usage?
     
  3. mikeathens

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    Well...it was an attempt. I was trying to base it on stove temp and stack temp, making some assumptions (like constant temps and 24/7 burns) to show how much loss occurrs up the chimney. But, since I'm not in R and R and have never really considered calculations like this, maybe i'm way off. Maybe someone else can pick up and make it work right? I assumed air and not wood smoke exhaust, I assumed 5 cfm, maybe this is a lot higher number (base it on chimney velocity and cross sectional area). blah blah balh...
     
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  4. Rhone

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    I haven't really looked this post much, but did anyone pick up on this winter was tropical for many of us so you can't compare a new cat stove in this winter and saved wood to a non-cat stove used in the normal or harsh winters of past? I didn't change stoves and my wood use is 25 - 40% that of last year. I put my money on the reason being that October, November, December, and January was like 50-60F and I've never seen flowers coming up in January thinking it's spring time like I did this year. My neighbor looks to be doing very well on wood savings as well and they haven't changed their stove either.

    I don't believe there's a difference in efficiency one way or the other. I mean, a secondary burn stove has a longer path for gases to travel, and a longer burn path and more turbulance = better heat transfer from said gases. I read a study that pretty much concluded if cats are more efficient than secondary burn units it's only because they can engage and start burning a few minutes faster than secondary burn units. I'm not sure, as testing would have to be done because I can get my unit having secondary burn going faster than my in-laws can bring their encore up to temp to engage the cat.

    Elk likes to bring up efficiency with cats, and the argument is invalid. Cats are always tested BRAND NEW shiny unused in the box, compared to the AVERAGE lifetime of a secondary burn unit. See the problem, the argument "This unit when brand new outperforms the average of that unit". It's like saying, "My FRAM air filter when brand new performed 10% better than the average over it's life of the 3M's air filter". Um... you're comparing brand new performance to anothers average... how you can compare them. Tell me the average performance instead for the cat over its life and then we can talk.

    I'm sorry Mike from Athens I didn't understand your argument. I see it as a stove-pipe thermometer doesn't care if you're using a cat or not. If secondary burn units have higher internal flue gas gas temperatures I would assume there would be a different flue gas temperature probe for the two models. But there isn't, 400F-900F is safe flue gas temps for cat and non-cat stoves and if a cat stove is showing 450F internal flue gas temps and a secondary burn unit is showing 450F internal flue gas temps... each with the about same particulates where is all the heat coming from out of the secondary burn unit out the flue? I see it as, a secondary burn unit burns the secondary gases inside the firebox, it has to loop to the front, up, then travel to the back, and then it can go up and out the flue pipe. A cat, the flue gases burn in the cat at the base of the flue pipe and out it goes. When it comes to turburlance, travel distance, and travel time the secondary burn units have the advantage. I however, don't believe them to be more efficient simply because I think both are designed to transfer as as much heat as possible and only let just enough heat out the flue to run properly.

    That's my $0.02, each has advantages and disadvantages and no winners or losers in my opinion. I wouldn't hesitate to get a cat if my wife wasn't the way she is, I love the look of the VC encore. I always think looks are always the most important, but depends if a family member is part of the 0.01% of the population who simply will without a doubt kill a cat if given a chance to operate one.
     
  5. mikeathens

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    You missed my point: Every non-cat stove I've been exposed to has a typical connector temp of 700 F - 800 F (flue probe) or so during the main burn, vs. a catalytic connector temp of around 400 F (flue probe) - I was able to practically hold my hand on the chimney of my small DW catalytic without discomfort. My point is that the catalytics keep more of the heat generated by wood combustion in the stove/house. The non-cats (both my DW everburn and hearthstone heritage) blow more heat out the chimney. If that isn't the definition of less efficient, I don't know what is. Also, a friend of mine has a catalytic 15 years old with the original combustor still working. Hmmmmmmmm....
     
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  6. treeman08

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    I hate the whole cat vs. non cat argument, but you have not done your homework on this description. As discussed earlier in this thread, the old retrofit systems as you described, were not good systems. My new stove has the same loop to the front, up, and then travel to the back through the Cat. At the back of the cat the temps are 500 to 1700 degrees. The configuration then pulls the heat out and as Mike says the flue temps appear lower.
     
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  7. Rhone

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    I still feel there's something strange. Did your previous secondary burn unit have a damper? There's a video posted by Roosterboy and as I recall in the video he had a flue probe and he turns his secondary burn unit down and on the video he maintains 450F. That was many months ago.
     
  8. Gunner

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    My flue gas temps in a non cat are between 300-600F by probe. At 600F flue the stovetop is 800*.
     
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  9. Todd

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    Mike,
    I tried making that point to Tom (the chimney sweep online) in that cat vs noncat thing he has. He just spun it like everything else I was trying to say. Anyway you are right. That is one of the first things I noticed, lower stack temps with the cat stove.

    When my stove is chugging along at 500-600 stove top, my stove pipe temp is 250-300. My previous non cats pipe temps would run 350-450 when burning those same stove top temps. That has to say something for efficiency. Somehow the cat keeps more heat in the stove.
     
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  10. Roospike

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    So if a cat stove has a surface temp of 500°-600° then the cat must be what 800° ? So the short distance from the cat to the flue pipe it goes from 800° to 250° flue pipe temp ?

    It sounds like to me that the cat get really hot when burning smoke and gas and then cools off 550° before going into the pipe .............That just doesn't sound right folks.
     
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  11. Todd

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    Your right, it doesn't sound right. Your flue pipe temp of 250 is surface not internal so it's actually more like 500 internal. Still there is a big difference from the cat temp of 800 to the flue temp of 500 and I don't really know why this is, but it's true.

    I'm not a wood stove engineer but maybe the cat is positioned at a certain angle that points up towards the top of the stove, and not directly towards the stoves outlet, so most of the heat gets absorbed by the top plate and the rest bounces off and redirects out the flue?
     
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  12. MountainStoveGuy

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    I wish there were more catalytic options, they work well in our altitude. One of the few drawbacks IMO is the clearance to combustables these stoves usually require. One thing about the non cats with the baffles up top, is that they keep the back relativly cool and they can sit tight in a small space.
     
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  13. TMonter

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    Lets look at Efficiencies:

    Fuel: Red Oak

    Ultimate Analysis % by weight:

    Carbon - 39.58
    Hydrogen - 4.30
    Oxygen - 34.50
    Nitrogen - .28
    Sulfur - 0.01
    Ash - 1.33
    Water - 20.0

    Losses:

    Unburnt Carbon Loss - 2%
    Unaccounted Losses - 0.5%

    Case 1:

    Excess Air: 50%
    Flue Gas Temp: 300F
    Thermal Efficiency: 81.181%

    Case 2:

    Excess Air: 50%
    Flue Gas Temp: 400F
    Thermal Efficiency: 78.032%

    Case 3:

    Excess Air: 50%
    Flue Gas Temp: 500F
    Thermal Efficiency: 74.884%

    Moral of the story:

    All conditions being the same, 200 degrees in flue temperature is worth a 6% gain in thermal efficiency.

    To be noted my typical flue temp inside the center of the flue is between 290 and 350 with the average being 305-310. This is on a Quadrafire 3100i non-cat stove. I haven't bothered with a flue temp on my englander 13NCL yet.
     
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  14. Roospike

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    Well that would make sense.

    Are the mentioned flue temps per cat vs non cat fact or where are the numbers coming from.

    I cant argue the point from a self experience stand point because i have double wall pipe and don't run a probe so i couldn't tell you for sure what mine are .
     
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  15. Roospike

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    If you think about it the difference sounds like with the non cat the flames are directed forward then around the baffle then next to the top and then out.

    With the cat stoves that i have seen they dont have this "S" Chanel and when the cat get hot it make the back of the stove hot ..........ie: higher clearance to combustibles.
     
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  16. MountainStoveGuy

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    what are they doing over at arbor site?? LOL



    "Thank you.
    I actually have checked them out and decided that I don't want a cat stove.

    I quote too much!

    Anyway, I'm a chemist (hold the applause) and a catalyst on a wood stove just doesn't make sense. The cat stoves I have seen have a damper/bypass so when you are starting or feeding the fire, the catalyst is not in use. Well, those will be the two times the stove will burn with the least complete combustion (dirty.) When any stove is at temperature and not starved for air it will burn fairly clean, even those old "smokers" or open fires. Sounds like a pain, especially with one more control to fool with.

    The non cat stoves that use air passages feeding the secondary burn are essentially the same idea, well, actually a better idea that accomplishes the same net result. Just without having to operate, clean, or replace cat-combs."
     
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  17. TMonter

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    There's a reason he's a chemist and not an engineer. He's not seeing the big picture.
     
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  18. MountainStoveGuy

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    LOL, chemists and engineers are my favriot customers ;)
     
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  19. TMonter

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    I have a lot of respect for chemists, but in my experience as a combustion/process engineer is they tend to get tunnel vision on problems and not look at the overall picture.

    The difference between a scientist and an engineer is that the engineer deals with reality, not just theory. We actually have to make the damn thing work.
     
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  20. jpl1nh

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    Sandor, kind of funny. I just asked this attractive woman I know to go with me to Woodstock Stove this coming Monday! Since I live in NH, its a nice drive. That's my idea of romance. Get to find out what kind of woman she really is, cause if she doesn't like wood stoves i'll still be lookin. Have my eyes on the keystone too, and I think you just answered some of the questions I have about their ability to give off smaller amounts of heat. I love the way they look, cause its front and center straight ahead inside my fornt door and the centerpiece of my house. Hope my wife doesn't mind...
     
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  21. MountainStoveGuy

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    i have alot of respect for scienctist and engineer's, military pilots, teachers, etc. there are two on my list i would rather pull my eyeballs out with my bare hands then sell a stove to. :)
    this is said in fun, but ofcourse there is a itsy bitsy truth to it.
     
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  22. elkimmeg

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    Rhone You failed to factor the hrrizontal burn path when the damper is engaged it forces the smoke path downward in the front then draws it over the hot v coal bed
    this does two things burns off some of the smoke then super heats the rest and introduces it into the Cat combustion chamber At the same time secondary air is channeled threw and around the heat plates super heating it also both the smoke is heated and the secondary air entering the cat secondary burn chamber the smoke path is lengthened by drawing it down over the coal bed then it enters the secondary cat chamber from underneath A cat can achieve up to 1700 degrees which does a decent job of finishing off the smoke before it exits Super heated air is introduced and adjuster by a thermatic probe in the secondaru=y cat chamber. ITs not just the cat but a total design that works ITs just not the cat but the secondary air control adjustment that produces the long productive burn time.

    I pointed out these Cat stoves are nothing like the early add on cat combustors but well designed stoves Be it a Blaze king Woodstock Vermont castings Or Buck stove.

    Research for Combustor improvement is also moving forward thday they have expanded and lowered the ignition range VC has told Goose and I there is even a better super combustor far more effecient than what is on the market today Instead of ceranics coating it is of stainless steel. Note VC re-certified its cat stoves till 2011. When the cost of manufacturing these super cats become economicaly feasiable , they will appear in stoves. There are said to be far more durable and effecient.

    Also not noted here is secondary combustion in non cat stoves is intermitten once fire box temps drop below 1000 degrees secondary combustion ends add more air bring up the firebox temps again you will gget another round of ingition. the cat tends that onec fired off it tends to continue ignition and it is a lot easier to maintain 500 degrees or 380 the over 1000 for any lenght of time
     
  23. Todd

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    I don't know how most cat stoves are designed but my stove is similar to a non cat design. It has the primary air run down the glass, back through the fire box, up the back and beneath the baffle, and like a non cat there is a opening in the front of the stove forward of the baffle, but instead of an opening I have the cat combustor. So there is an S pattern and there are secondary flames before it reaches the cat.
     
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  24. DriftWood

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    I can see a place for a hi-bread Cat stove with secondary air tubes before the cat in the fire box. It would be a very clean buring stove during worm up, with small fires and at themp. Cleaner through the burning, heating cycle. Has any one seen a wood stove like this any place in the world.
     
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  25. Rhone

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    Thanks Todd, good post. I, like Roo have not seen or heard of an "S" shaped cat stove and find the fireview design pretty interesting. The cat stoves around here are Vermont Castings, in particular the one I was talking about was a brand new VC Encore (I wasn't referring to first 20+ year old cats). Correct me if I'm wrong Elk but after the gases burn in a VC cat, it's up and out the flue, there is no "S" shape or forcing those super heated gases to come to the front. I think Craig once called them rear top heaters, as most of the heat comes out well... the rear top. Todds setup is interesting, most of the heat should be the front/top.

    As for efficiency and wood savings, I do think cats are a little more efficient but I can't understand how it would be as high as being implied. I know it would be better for the 2-3 fires a month my logs collapse on themselves and extinguish the secondary burn (a cat wouldn't be affected). But, that only translates to reducing my heat output by up to 30% for 2% of my fires, which I think is 0.5% total savings, nothing significant. I'm sure there's those days you let the fire burn and forgotten to engage the cat, or remembered much later. As for cats keeping the heat in, I can see that because cats restrict air movement so in essence slow it down from escaping. The "S" path for secondary burn units should also add resistence as well, a damper does to. But, a cat when lit is normally between 1400F to 1700F as Roo was saying if sending gases through that much heat and it's only 250F-350F by the time it reaches a probe there's some serious heat transfer going on. I'm certainly not the expert on that though, my unit likes to be run hot. Maybe because I have an insert with a 220 cfm blower (bigger than most), maybe because it's soapstone lined, maybe both but if I burn my fire to last 6 hours my house 12 hours later will be warmer than if I burn it in 4 hours or 12 hours. So, I don't care much about temps, my aim is more for the 6 hour burn. Anyway, the fireviews cat position is pretty darn cool being in the front. I found this
     
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