Production Woodstock IS

Only 2 logs in the stove tonight and the air intake plates are quite vocal. It's tough to describe, but it sounds like a cold winter wind howling through the trees. My damper should be in any day. I'm expecting the firebox to be more controllable, and some mentioned I may even get more heat out of the stove.

 

It will be time for the first IS fire of my "sophomore" season this weekend! I've been tempted on a couple of cooler days we've had, but it wasn't even cool enough for the furnace to kick on, so common sense won. (Doesn't always happen!)

 

Um, I don't understand............

 

Yep, think of it another way: the stuff that forms the dangerous creosote is also what fuels the catalytic combustor, and if it's burning properly there will be no gasses left in the exhaust to form creosote. These volatile gasses are expended by the midpoint of the burn when the 'off-gassing' stage is done and you'll see all the temps start dropping. This is called the 'coaling stage', where it's mainly just coals burning down.

On the way up though, the "risk" period as you say, realize besides the cat temperature the cat can still be overwhelmed with too much smoke for it to handle, or if there is too much draft the smoke will be passing through the cat too quickly to fully combust, so there is just a little more than get the temp up as fast as possible but you got the main idea down. I mean you still want to get it up as quickly as possible, just don't expect a clean burn until it's settled out and cruising. If you just engaged the cat and have the throttle wide open and go outside to check on smoke you will likely still see some smoke.

 

Yes, the goal is to get the cat. lit and 'eating' smoke fairly quickly. But the real risk with these stoves is exactly what you experienced earlier- either not having the cat. light- off at all or light- off then stall (fall below operating temp. range). Then you end up with a smoldering, dirty burn with all the debris going up the flue. What you want is pretty much what your temp. chart showed: the first few hours of the burn, the cat. was considerably hotter than it was later in the burn, and this indicates that the cat. was alive and working, burning all, or at least <hopefully> most, of the creosote.

To that end, I find the two really important temps. to monitor are the firebox temps. somewhere near the top, and the temp. just above the cat. What you are looking for is a large difference between them, and this is the best indicator that the cat has ignited and is consuming smoke. That said, the only reasonable way I know to get a probe in the firebox (Boys!) is to drill a hole in a new stove, and I fully understand that a lot of people either cannot or will not do that, and I do not blame anyone for not wanting to do it. I put an 8mm threaded hole in my own stove should I ever sell / trade the stove in, I will plug the hole with a bolt and tell the person(s) getting the stove that the plug is there. It is not visible (under the I.S. sheetmetal) and would not cause a problem but again, I understand that many people do not want to modify (or as some say, hack into) a stove, especially a brand- new, rather expensive one.

Brian

 

I have a digital dilemma. I replaced my Condar mechanical probe with a digital thermocouple probe (TC) for the cat. The TC is showing anywhere from 100-200 degrees lower depending on the value. After some quick trials last night, I've come the conclusion that the Condar probe is off by a bunch. Here's some background:

1. The digital readout I am using was just calibrated and is within 1 degree at 1000F.
2. I used 2 different TC probes and got the same reading.
3. I have noticed that the cat doesn't light until the Condar is showing 700+.
4. When the Condar is showing 200F as it cools after being removed, it is just warm to the touch. That's usually around 100F.
5. Condar and TC are both 4". The TC is stainless steel with TC in end.

The final data point that drove me to this conclusion was this morning on a semi-warm stove. TC probe said 314F. Condar said 450F. Opened the stove top and shot the radiator with IR gun.....285F. Shot the general area of the cat underneath the radiator and got 296F.

The stove went nuclear over the weekend (or so I thought). Condar was showing 1500 and STT was showing about 625. I'm thinking actual cat temp was about 1300F.

Here are some numbers from last night.
About 15 minutes after cat engagement: Condar 1050, TC 850, Front of stove next to TC hole 375, Flue (probe) 365
After 1 hour on overnight setting (3rd notch): Condar 1100, TC 1000, Front of stove next to TC hole 470, STT 410, Flue (probe) 390.

Thoughts?

 

Well, I think you had a very poor measuring device (like a rope with knots in it every arm span or so) and were using it to gather data. Then you got a much better device and are now getting data that is far more accurate; actually accurate for all intents and purposes. Those mechanical clock spring devices that most of us have on our stoves are not only notoriously inaccurate, they are so slow to respond that they are worse than useless when used to watch after making adjustments to a stove because they do not reflect actual changes quickly enough to stop us from making further adjustments to a stove when the previous adjustment has already had the desired effect.

My thought would be to use your new thermocouple and be open to the idea that it (or they) are really reflecting what is happening and giving you accurate data. Unfortunately, the memory of the old 'data' from the incorrect reading devices gets in the way when seeing what is really going on- or at least it did for me. When I first put thermocouples on a stove some years ago, I was amazed at several things, one of which was how fast fuel temps. really can rise given a stove with a lot of bottom draft; after watching a mechanical thermometer slowly climb and adjusting the stove so as to keep the flue gasses below about 750F, I found out they easily and often exceeded 1,000F long before the mechanical thermometer displayed this information. The second huge surprise is that small changes in draft, for example, have an immediate effect on how a woodstove operates even though several mechanical thermometers would not show such changes for several minutes. And just like you, I have had cat. temps. 'seem' far too high, actually worrying me a bit, and then adjusting the stove several times and much too far to slow the combustor down when in actuality, 1) the cat. was not really overheated and 2) the first stove adjustment had arrested the temp. climbing and actually started to reduce the temperature making further adjustments both unnecessary as well as, well, incorrect.

Thermocouples and electronic amplifiers to read them are like giving someone with terrible eyesight glasses for the first time- that person suddenly realizes the world is really not what he / she thought it was. As a friend of mine put it, after getting his first set of glasses in his 30's, "hey, there are leaves on all the trees!" and he was really not kidding.

We have been burning wood for heat for thousands of years but it is really only very recently that anyone has really studied HOW wood burns and what makes it burn well or poorly. And only very recently that us regular, plain ole' mortals can have access to the tools needed (thermocouples being the best example) to learn how to burn wood and regulate a wood stove properly, at least in my opinion and speaking for my own experience. I have been burning wood since the 1970's but only started to learn how to do it more properly and repeatably in the last few years.

Just my opinion but you are on a great path to improve your own woodburning with much better, faster and more accurate instruments to see what is really going on.

Brian

 

Whew.
Yep.

 

I am killing time waiting for the crane to show up. Bored and surfing the 'Net. You poor folks on the very few forums I visit may have to put on your seat belts.



Brian

 

Thanks Brian. I thought I could coax you out on this one. You pretty much validated what I thought was going on. Being an engineer I try to approach things logically, but I don't have the instrumentation experience you do and wanted a sanity check.

The quick response of the TC is what made things seem more extreme than they were. Top down, cold start fire was showing 1200F from flame impingement on the TC when the Condar wouldn't have even started moving. I'll have to pay more attention to STT and flue temps with cold startups due to the TC picking up flame temps so quickly. Cat engagement caused an immediate drop in TC readings that started climbing again as the cat came up to speed. No way the Condar picks this stuff up. I've had TC on flue for a while and pretty much know what it is going to do. Now it's time to learn the ins and outs of the cat as it goes through a full cycle.

Once I am comfortable with the setup, I plan to add high side alarms to STT and flue temps. I might even try low side alarms on STT to signal time for reload. My stove is in the basement, so it might save a few trips up and down the stairs. A wifi camera might just be the finishing touch to allow monitoring of temps from the living area. Perhaps some data acquisition hardware down the road.

Boys and their toys...................

 

A little wordy, but pretty much spot on from my experience. I've wondered why modern stoves don't have these TCs as a matter of course. Other heating appliances have all sorts of monitoring and control devices.
I imagine most folks just want to start a fire and walk away for a while.
I like a good read now and then.
Caveat...I don't have a cat stove.
Now that I have a newer stove, I have yet to see an overfire. Just doesn't happen.
A low side alarm could be useful.

 

Hey, slick idea on the wifi camera watching the readout- I like that idea a lot!

What I have learned using data monitoring on a cat. stove is that the crucial thing to watch are actual firebox internal temps. and cat. top temps. It is actually very easy to know exactly what is going on after watching it for a while and learning the two different ways it can behave. Basically, close the bypass and watch the cat. temp. fall, wait about 20 seconds and if the temp. bottoms out and starts to rise, the cat lit- off and all is well. If the cat. temp. keeps dropping, or especially if it accelerates in how fast it is dropping, the cat. is not going to light- off and it is time to re- open the bypass and get a better fire established. When things are prefect, as soon as the bypass is closed, the firebox temps. go down and the cat. temp. hesitates for a few seconds and begins to rise- that is the ideal situation and at that point I can cut the draft back and actually put the stove into normal 'running' mode, knowing the cat. is lighting and the stove will run clean and efficiently. But it takes quite a while actually watching the readouts to figure this out- at least it did for me.

Brian

 

What do you monitor for cat engagement? The cat TC is a bit misleading on a cold startup due to the flames and the STT lags way behind on a cold start. It's probably a bit more accurate on a "hot load" due to everything already being at operating temp. I have been watching the flue temp and Condar probe, but now I'll have to rethink my approach.

 

Just my opinion but I think cat. stoves are better for people who want the most out of heating with wood and are willing and able to spend some time learning how to do it. Non- cat stoves are better for people who basically want to 'set and forget' a woodstove. I have several friends who burn wood without ever touching the draft at all; one runs his wide open and lets the stove do whatever it will do and another sets his for 'low and slow' and just loads and lights. The last guy often fills his entire neighborhood with really quite thick smoke and has actually clogged his chimney repeatedly with creosote (I mean stopped it up 100%). Neither person would benefit from a cat. stove IMO.

Unless, of course, the whole process could be automated.....

Brian

 

Yep. Which is why I want one.

 

Flue temp and firebox temp. I hold the flue at 650F or so and wait until the firebox is up over something like 800F and then close the bypass. The firebox temp. immediately drops and I watch the difference between firebox and cat. top temps. to make sure the cat. is lighting. If the cat. is igniting but not very quickly, and this usually happens with a new fire, I leave the draft wide open until the firebox temp. bottoms out and starts to climb again before cutting back on the draft. If the cat. takes off very quickly, usually on a hot- reload, I set the draft for the long burn and walk away.

Brian

 

On the other hand, isn't that what cat stoves do best, once you learn how to run them?

 

No, I mean they are set when they are new and left with any / all adjustments untouched for years or decades. I think a lot of people use wood stoves in this manner- open draft (and abandon it for all time), place wood in stove, set wood on fire. You get whatever you get regarding heat, efficiency, burn time, etc., etc.

Cat. stoves require some work on the operator's part: if the bypass is left closed and a fire is lit, it is likely that it will not actually catch, smoke will spill into the room, and after a couple of these events the cat. will clog completely with sticky, black creosote. If a cat. stove is used with the bypass left open from day one, then it is not really being used as a cat. stove at all. So..... cat. stoves are better for those who want the most out of a woodstove and are willing to put some time and effort into getting it. Non- cat. stoves are better for those not wanting to spend one more second than necessary in burning wood, just like a fireplace. All in my opinion of course.

Brian.

 

Maybe but hey, look at all the reading time you saved just today by NOT reading either 'Moby duck' OR 'War and Peace'. Dem dare is long books so you really are way ahead in reading time spent. That is, of course, assuming you have not / will not read either of those two books today. So perhaps my posts have distracted you from those books and I have therefore provided you with additional free, non 'reading lost' time today. Use that time wisely my friend, use it wisely.



Brian

 

Like I said, I like a good read now and again.