Just Over Fed My Cat

I let mine roar every time I reload. I don't believe you had any kind of creosote or flue fire with the Fireview.

You may need a damper to calm the draft down on a 28' flue. i have one in mine and always use it.
Why are you apposed to a damper in the connector pipe?

 

1 foot single wall with key damper installed.

 

I do have the key damper. Have not felt the need to use it - Woodstock suggested not to have it but did admit that in some cases some people need them. Today was warmer than many of the days so the draft should not have been as strong as other days. However, I had always loaded normal size pieces, never a load of mostly 2 inch cherry and elm pieces.

The other problem with key dampers is knowing exactly when to use them. High wind days are obvious choices, but do I really need to use it on simply cold days if the stove setting is adequately controlling the burn? I really don't know with this stove; with the old one it was use the key damper or reload every 2 hours instead of 4.

 

this sounds like the answer to me.

I'm sure there is a formula and a way to test the draft but doubt anyone uses it. Key hole dampers only close to about 80%. I believe the damper will help hold some heat down in the stove rather than let it go up the flue

I usually stop at a half a load when I'm using the kiln dried pieces. It gets plenty hot. I will close the damper pretty far even on a cold start if I'm just using kiln dried.

 

If the fire is catching pretty good, and I have the air open enough for it to "roar," my pipe is going to be overheated in short order. Do you have a flue meter in your setup?

 

yes. I usually heat it up pretty good on a reload too

 

Decided to take a look inside Garfield's belly after yesterday's fun. Here are some pictures.

Spoke with Mike @ WS about it and he said there was nothing wrong with my load of smaller pieces but that the behavior was typical of an overdraft situation; the sound is from flames burning between the combustor and connection pipe. Only thing to do once it starts is to give the stove a bit more air. He told me of a customer of theirs that had a 40 foot stack that required two key dampers to enable typical operation of the stove. In my case he recommended I run the stove using the key damper until I find a damper position that gives the results I am looking for. He could not provide me any "rules of thumb" - just that taller stacks like mine can experience this overdraft at times.

TurboDiesel , would like to hear how you use your key damper.

 

Have you got a surface meter on the connector pipe, a probe, or what. How far up from the top of the stove is it? What temps do you generally run on it?
I tend to ramp my stoves up to temp moderately. I might have the air wide open, but once the load starts catching and flames are reaching the top of the box, I will start cutting the air. I don't want to see big flames sucking hard into the connector pipe. I like to see a lively fire in the box but not a raging one. I don't like to subject the bypass opening area or the pipe to excessive heat.
Stoves are rear-vented into the fireplace so I can't have a surface meter at the recommended 18" above the stove top; I have to lay the meter on top of the stainless tee snout, about 8" past the end of the flue collar. I will run that meter up to about 500 or 600, then hold it there until I have the probe and stove top temps I need for a light-off.

Interesting. That was one of my thoughts, as I posted, but I couldn't see how it could happen. I guess the smoke blows past the combustor but then with a hot cat, the smoke ignites on the other side.
When it started making the blow-torch noise, did you cut the air all the way and the noise persisted? If so, I think the pipe damper will give you the added level of control you need. My SIL's Fireview stack is about 21' with two 30* elbows through the roof trusses at the top. I can tell that closing the pipe damper definitely has an effect...

 

When this happens it is seeking oxygen and starts sucking it in from the air intake and likely from the stove pipe joints all of which adds to the sound being produced. It really isn't as loud as one might expect based on calling it a torch or jet engine; but when it is louder than normal operation you would notice it. My command center is perhaps 7 feet from the front glass when I swivel my chair around so you would notice it from that distance, but perhaps not if there was background noise like a TV or radio.

Well, I actually first turned the key damper to perhaps 2 o'clock then closed and it had no impact so I opened back up after 10 seconds or so and then increased the air slightly. Then proceeded to go outside to look up to the cap and saw just a tiny bit of smoke (couple cigarette's worth - not much but I have never seen any until then) came back in to watch the firebox engulfed in flames and checked STT and flue temp and both were in cruise range; couple minutes later it was over but the firebox had some awesome secondaries for some time after the torch sound went out.

Going to start using the key damper using the following guidelines until I can find another way to better tell me how to set it:

• < 30 set to 1:00
• < 20 set to 1:30
• < 10 set to 2:00
• < 0 set to 2:30

 

I have found the opposite, almost all of the newer non-cat stoves allow full throttle wide open air supplies to the secondary air system which is those tubes on the firebox roof. That is a LOT of air. Many, including my NC30 also allow unregulated full throttle air into the doghouse at the bottom of the loading door to feed the fire with no control. In addition, most if not all, primary air controls do not close completely and allow a significant amount of air through at their minimum setting. These air sources combined take away control and are the cause of many runaway non-cats. Anytime you can't control the temperature of your stove it has run away IMO. The older stoves that were in good condition like say a fisher, were able to be closed off much more completely and allowed to smolder for long periods. Ancient stoves used nothing but a key damper in the flue outlet to regulate burn rate.

Now modern cat stoves are able to burn cleanly without all of these extra air sources so they are designed to allow the user to really reduce the combustion air.

As woody pointed out, this is not true. I can add that no Blaze kings have air supplies feeding the cat.

 

sorry Woody, missed this earlier.
I do not have a meter in mine. I made it sound like I did .

I run 2 surface temp gauges. one at 16" above the outlet, on the connector pipe, and another on the stove top. Left side of the cast divider and about 1/3 back. so its right above the cat.

I will let the fire start to roar with the door cracked open and suck the flames up the pipe till the pipe temp gets to 3-400 surface temp.
I then close the door and cut the air to 2.
Let the fire continue to burn hard till the temp climbs to 500 close the damper to 45 degrees and cut air to 1.5 to 2, wait till the cat fires and begins to burn the wood from the top then close the bypass and set air down to 1-1.25 or as needed for the current weather. Tonight when the snow was really starting to get heavy I had to leave the damper open 100% and set the air at 2 to have good flames on the box.

every time I bring in more wood, all the settings change. type of wood, moisture content, where the wood was stacked, current weather, all affect the start up times and temps. just when you think you got it all figured out, you get another new lesson.

 

I very often Spring and Autumn burn with only very small twigs and branches up to about 1 1/2 inch diameter...keep the rest for winter. I have a very strong draft, and have to watch the stove very carefully initially or exactly what you describe happens. Can be scary sounding, and the inside flue temp can and does get to 900 incredibly quickly; if that happens, closing the air completely stops the noise immediately, and the firebox slows to substantial secondary flames within half a minute or so. However, if I watch the stove after lighting the fire, and close the damper and air and engage the cat as soon as the flue gets to cat temp, then this never happens. Just too much surface area burning and producing more smoke and fire than the stove can handle, in the presence of too much air. If it happens after the cat is engaged, you need to both cut your air and utilize your damper on a regular basis. If you don't get too much smoke going through the cat for the cat to handle, I don't think this will happen once the cat is engaged. Never has with me.

I love heating with the small stuff during shoulder season: keeps my good wood for when I need it, and produces a fire that burns for about two to three hours, and leaves a warm stove to continue heating. All the heat I need for shoulder season. On a slightly colder day, I'll add a small split. As I approach winter, I add a few splits. Switched from the branches to firewood Dec. 28th this year, and still have a box of branches inside that I have not had to use because the fire has maintained coals since 12/28.

Just be aware, the twigs and braches ignite and get to temp very quickly, and the stove should not be left until everything is engaged and air is turned down, AND the stove should not be allowed to get above 250 stovetop temp before the air is shut down.

But I see no reason for you to be reluctant to burn small stuff. Saves some trees.

 

Your 3 take aways are all good. Love the hybrid and blend of best of both worlds aspects. Will likely see more in the future.

 

Well we certainly agree on the definition of 'runaway' and also that it is a bad thing, even if overheating does not happen. It sounds as though you believe, as I absolutely do, that a woodstove should be able to be throttled directly (via damping mechanisms rather than modifications or 'trickery') to reduce its temperature even if it is operating in the allowable range but running too hot for the user's wants or needs.

As far as wide- open secondaries, that should be controlled by just how big the air passages in the stove are in the first place. Certainly there are many stoves on the market and I would not claim to be knowledgeable about all or even most of them but I would also expect any modern woodstove to the throttle-able, at least to the point of reducing the fire to what I would call a 'lazy' or very low burn fire, assuming it was not loaded full of dry kindling in the first place (that would be operator error IMO).

That said, if a stove cannot be throttle reasonably, then stove pipe dampers should go a long way to make it controllable.

Brian