Tonight, I miss my old stove..(BKK questions)

[fdegree]

I have to run the blower for anything above about 2.25. It may be on low, but without the air flow, the Cat will want to max out.

My geographical location and home are very different, but I have this same scenario. I don't have a surface thermometer, nor stack thermometer, so I can't make a comparison to those concerns. But, if I turn the t-stat much past 2.0, the cat temp rises significantly and I have to run the fans to keep it from going too high. This is the case for me, until the room gets too warm and t'stat backs down on the draft, or the wood load drops and it is not producing much smoke and heat. I also have the Condar cat probe with the number scale, and I try to keep it from exceeding 1700*. When I replaced the original cat probe, with the Condar, I checked to make sure they pointed at the spot, in and out of the stove...haven't checked them recently.

My house is only 6 years old...reasonably insulated and sealed. Given ample time, my house will warm up. But, I have to run the fans on a setting past 2.0. So, I'm wondering if this is normal and B-K's problem is the envelope of the house.

I realize this is no help, just expressing a similar experience

 

[SolarAndWood]

Definitely not normal. I don't have to run my blowers no matter where I set the t-stat. For any given position of the t-stat, the only difference with the blowers is that the burn time goes down by a third and a lot more heat comes off the stove.

fdegree, it kind of sounds like your stove might be running away a bit in the beginning of the burn cycle. Have you done a dollar bill test?

 

[fdegree]

Definitely not normal. I don't have to run my blowers no matter where I set the t-stat. For any given position of the t-stat, the only difference with the blowers is that the burn time goes down by a third and a lot more heat comes off the stove.

fdegree, it kind of sounds like your stove might be running away a bit in the beginning of the burn cycle. Have you done a dollar bill test?

I have not done the $ test...I just reloaded, I'll try it tomorrow evening before the next reload.

On a new reload, I usually leave the t'stat on 3.0 - 3.5 until the entire firebox is completely filled with flames. By doing this, most of the splits get charred pretty good, so when I back down on the t'stat there is a lot of smoke...driving the cat temp up. I do this because I don't have the driest wood...around 20% - 25%. By following this procedure, and as long as I have a full load, any setting above 2.0 results in high cat temps, requiring the fans to keep it under control.

When I reload at night, and the outside temps. drop below 20*, I have to increase the t'stat setting above 2.0 in order to keep the house above 70*. After a few hours I can turn the fans off and the cat temp will settle below 1500*.

Could my wood condition be a major contributor to this phenomenon? Could wood condition be contributing to B-K's problems as well?

 

[SolarAndWood]

I deal with a lot of chunks and uglies because of the price I pay for it. However, I refuse to stack it and usually burn it a lot sooner than I should. I throw it on top of at least 3 or 4 small dry splits but it is still a PIA and I always burn it hot, like 3-3.5 for most of the burn. I only burn it when its above 20 and not blowing too hard. The difference is night and day between that and when I drop a load of 2-3 year split stacked under a roof in. Then, its let it warm up for 10, close the bypass and let the cat light off, then set it wherever I want and forget it.

That doesn't explain the need to run the blowers to keep the cat from overheating though. Even when I am burning crap, I don't experience that.

 

[Renovation]

I deal with a lot of chunks and uglies because of the price I pay for it. However, I refuse to stack it and usually burn it a lot sooner than I should. I throw it on top of at least 3 or 4 small dry splits but it is still a PIA and I always burn it hot, like 3-3.5 for most of the burn. I only burn it when its above 20 and not blowing too hard. The difference is night and day between that and when I drop a load of 2-3 year split stacked under a roof in. Then, its let it warm up for 10, close the bypass and let the cat light off, then set it wherever I want and forget it.

That doesn't explain the need to run the blowers to keep the cat from overheating though. Even when I am burning crap, I don't experience that.

It sounds like FDegree at least is burning a full firebox worth of "cr$p". Have you tried that? I'm just trying to be helpful, and have an apples-to-apples comparison.

 

[SolarAndWood]

I load the firebox all the way up every time, whether its September or January, crap or primo. I don't think either of their stoves are operating properly if they need the blowers to keep the cat from overheating. I'm not sure I could overfire my stove if I wanted to as long as I close the door.

 

[bogydave]

Could be as simple as the catalytic combustor is bad.
May need replaced.
The manual talks about how to test.
Only burn untreated dry wood. No trash, plastics, colored paper etc.

 

[Renovation]

I load the firebox all the way up every time, whether its September or January, crap or primo. I don't think either of their stoves are operating properly if they need the blowers to keep the cat from overheating. I'm not sure I could overfire my stove if I wanted to as long as I close the door.

Thanks. Being a prospective owner, that's great to hear.

With reference to the post above, have you been careful not to poison your cat?

 

[SolarAndWood]

Other than only burning cord wood and giving the less than dry stuff a good burn with the bypass open, not really. I've got a little over 10 cord through it now and it still lights off like the day I bought it used. The original owners were burning some less than dry wood in it and complaining it didn't put out any heat but a couple loads of dry pine took care of it.

 

[jtb51b]

Wet wood will cause a lot of unforseen problems. With a full load of wetter than needed wood you cannot get the heat required to cause the thermostat to respond quickly and correctly.. I have done a real world comparison with wetter wood and dryer wood and I promise you the wetter wood burns up QUICKER and does NOT heat the house as well as the dry wood. That in itself tells me that the wetter wood requires more air to burn and therefor more heat goes up the hole. It DOES matter what goes through the cat to create heat, even though people say a cat burns "smoke" it really burns exhaust gasses NOT MOISTURE.. Moisture passes right through the cat and up the stack just like it would with the bypass OPEN. Now, the way I have it figured is that moisture is superheated by the cat burning the other gasses and therefore passes up the stack and out without a lot of time to buildup creosote (I.E. even with the moisture going out, theres nothing to mix with it).. Anyhow, just one mans take on the age old problem of wet wood, doubtful it will help but I had to put it out there!

Jason

 

[Beetle-Kill]

Ohh yeah baby, we have some progress. Stove is still the same, but the heating issue is being addressed. Yup, insulation and air encroachment are playing a huge part with me. I've charted it for the last 3 hours, 10 - 15 min. increments, but I'll not bore anyone with that. Needless to say, after we discussed last nights discussion here, she hung a blanket over an open doorway to the upper hallway- going to the second bedroom. When I got home tonight, I walked into warmth. (what the ...?) So, out comes the pen and paper. The front room is warm- 71.5 and climbing on a fresh reload. It was over 72 when I grabbed the temp. control and put it up in the upper hallway, 15' from the covered doorway. After 26 min., it was @ 60.9 and dropping. Now, back in the front room, 71.7 since I started typing. I don't think its ever been this warm, for this long, in this room- this season. I now have a target. I still have issues with the stove, but addressing this situation is so simple, a cavema..........oh crap, I'll shut up. :down:

 

[Renovation]

Yup, insulation and air encroachment are playing a huge part with me.

Yay on the improvement!

Remind us what your house and insulation/sealing are like?

 

[Beetle-Killer]

Gimme' a sec., comp. says I'm logged on with a different tag.

 

[Beetle-Killer]

RenoG- heated area is about 2300'. The main area was a cabin, transplanted in the 50's. The front room and garage/ upper bedrooms were added in '76. This place is odd to say the least, but it grows on you like a fungus. The stoves operation hasn't changed, but hanging that blanket over that upper doorway was a dramatic improvement in heat retention. I mean HUGE!! Insulation currently is minimal, lacking in some areas, non-existent in others. That's exagerated, but the attic areas are about R-30 at the most. When I talk to BK tomorrow, I'll post. Until then, I'm gonna enjoy the extra warmth (yep, lower your expectations and ....well..sleep easier?)

 

[learnin to burn]

Great on the improvement! That's one of the places I was going this morning before I had to run. All the cold air flowing into your house is being sucked up by the fans then going right across the top of the stove which explains the big difference between stove top and flue temps.

One thing that puzzles me is why many people think that turning the fans on and blowing air across the top of the stove and directly onto the coil of the cat prob would cool the cat itself? Unless I'm missing something it just doesn't make sense.

That being said I would turn the fans off and see if that improves the heating a bit more even if it is just for part of a burn cycle.

 

[Renovation]

One thing that puzzles me is why many people think that turning the fans on and blowing air across the top of the stove and directly onto the coil of the cat prob would cool the cat itself? Unless I'm missing something it just doesn't make sense.

Hey LTB,

Kudos on your thoughtful and helpful posts. :thumbsup:

If you're talking about cooling the cat by cooling the cat housing, I believe it does make sense. (Not knowing the geometry of the Blaze King, I don't know if the air from the stock blowers cools the cat housing.)

From my understanding of heat transfer, in an open loop system (i.e. with a constant amount of energy being pumped in = constant burn rate), that is transferring heat from a hot object (the cat) to a cold one (the cat housing), if you make the cold object colder, the hot one gets colder too. Like your living room when your stove is on a constant burn, and the outside temperature drops.

No, it's not very intuitive, and hard to imagine that something burning at 1500 degrees is going to cool off because a shield on the other side of a bunch of intensely hot gas gets colder, but I believe the laws of thermodynamics say it's so.

It's a hard concept to grasp, and there have been similar discussions on fans cooling combustion temperatures, which I believe they must.

That's not to say how much the cat cools off, if it's significant, etc. I'd guess that it would be a significant amount with sufficient airflow, but that is admittedly just a guess.

Thoughts?

 

[Beetle-Kill]

You guy's are killin' me- but only from the standpoint of injecting trains of thought that will keep me from sleeping, at least sleeping soundly. Learnin- isolate any areas you may think are acting like a heat sink, but don't do them all at once. Or- do them all at once, then remove the blocks one at a time, to find where your biggest areas of heat loss are. I can't believe the difference a single hung blanket has accomplished, espescially in that location. And yeah, the idea that blowing air across a hot surface would cool the internal temps. of a combustor, that has always seemed to be , well,- odd. We have some very smart people here, I'd love for them to chime in on this aspect of the Cat. thermostat/ stove/ blower thing.

 

[learnin to burn]

One thing that puzzles me is why many people think that turning the fans on and blowing air across the top of the stove and directly onto the coil of the cat prob would cool the cat itself? Unless I'm missing something it just doesn't make sense.

Hey LTB,

Kudos on your thoughtful and helpful posts. :thumbsup:

If you're talking about cooling the cat by cooling the cat housing, I believe it does make sense. (Not knowing the geometry of the Blaze King, I don't know if the air from the stock blowers cools the cat housing.)

From my understanding of heat transfer, in an open loop system (i.e. with a constant amount of energy being pumped in = constant burn rate), that is transferring heat from a hot object (the cat) to a cold one (the cat housing), if you make the cold object colder, the hot one gets colder too. Like your living room when your stove is on a constant burn, and the outside temperature drops.

No, it's not very intuitive, and hard to imagine that something burning at 1500 degrees is going to cool off because a shield on the other side of a bunch of intensely hot gas gets colder, but I believe the laws of thermodynamics say it's so.

It's a hard concept to grasp, and there have been similar discussions on fans cooling combustion temperatures, which I believe they must.

That's not to say how much the cat cools off, if it's significant, etc. I'd guess that it would be a significant amount with sufficient airflow, but that is admittedly just a guess.

Thoughts?

What you are saying makes sense but I'm not sure it works that way with the BK. Picture the top of the stove and under it is a rectangle chamber. The chamber is closed on 3 sides. In the front of the chamber(front of stove) there is a large area cut out of it where the cat sits. (it goes without saying the whole thing is steal) Before the cat is put in place it is wrapped in a gasket, then it is placed in a metal holder then wrapped in another gasket. Now it is placed in the front of the chamber. Once the stove starts to heat up both gaskets expand to seal it in place. you now have 2 layers of insulation separating the cat from the metal surfaces so there isn't enough temp difference to overcome the insulation in this case.

The cat probe sits about 3 " behind the cat in the chamber. Assuming the air in the chamber can be cooled 100 - 300 degrees just by turning the fans on based on your explanation then the cat probe itself would reflect that temp change. Now the cat burns the smoke that enters it from the outside of the chamber, the more smoke the hotter the cat gets. With the fans off we'll say the t-stat is set on 2, and the stove top is 550, cat at 1300 with the t-stat up to temp for it to be closed. Turning the fans on now reduces the stove top to say 450 which then based on your explanation also reduces the air temp inside the cat chamber. The t-stat reads and responds to that temp change allowing a little more air into the stove which produces more smoke which in turn raises the cat temp. Now the cat temp is running a little higher until such a time as the t-stat reaches it's temp to close again. Then the cycle starts all over again until there isn't enough fuel left to maintain the higher cat temps.
In this case the cat prob is simply giving a false reading.

If you have seen some of S & W's posts about burn time, He says he goes through 1/3 rd more wood when he has the fans running. That's because there is more air burning the wood faster and producing more smoke making the cat hotter throughout the length of his burn cycle.

Sorry BK, I'm really not trying to hijack this thread

 

[Beetle-Kill]

Learnin- You GO boy, this is cool, don't worry about my dumbass. Interesting train of thought, well played. Can't wait for the responses. JB

 

[Renovation]

Okay BK, go ahead, egg me on! Here goes.

I was answering LTB's original question:

One thing that puzzles me is why many people think that turning the fans on and blowing air across the top of the stove and directly onto the coil of the cat prob would cool the cat itself? Unless I’m missing something it just doesn’t make sense

And in doing so spoke explicitly of open-loop performance, which ignores the action of the thermostat.

My point remains a simple one, but one that is often overlooked--cooling the outside of a stove cools the inside too, cat included.

Regarding that, and remembering that I'm still talking open-loop, I'd like to make one clarification. LTB said:

Before the cat is put in place it is wrapped in a gasket, then it is placed in a metal holder then wrapped in another gasket. Now it is placed in the front of the chamber. Once the stove starts to heat up both gaskets expand to seal it in place. you now have 2 layers of insulation separating the cat from the metal surfaces so there isn’t enough temp difference to overcome the insulation in this case.

To split hairs in the interest of insight, I do not believe that is precisely the case, for two reasons.

First, thermodynamics says that cooling one side of a conductive path (the stove surface) cools the other side (the cat), regardless of the amount of insulation. The more insulation the less the change, but there is still cooling. That said, if there is enough insulation along a particular thermal path, the cooling by that path is trivial, which may be what LTB meant by "there isn’t enough temp difference to overcome the insulation in this case."?

The second factor is that conduction by the cat mount is not the only cooling path--there is also radiation from cat to stove skin, and conduction by the flue gases, which carry heat to the stove skin. Both the "cool sides" of these paths are made cooler by cooling the stove skin, and will cool the cat. How much can be debated, but it does happen, which is my answer to the original question. (In fact I was going to suggest you try blowing a fan directly on the area around the cat.)

LTB went on to talk about closed-loop dynamics, on the longer time scale that allows the thermostat to react, and his description makes sense to me. However, closed-loop operation involves so many variables that I don't think anyone could accurately guess net cat temperature response--up? down? none? It depends on how the stove is tuned, production tolerances, flue, time frame, etc.

My original point remains--there is a sensible explanation for how cooling the stove surface can cool the cat.

Happy? Awake?

In fact the specific issue is fairly trivial, except for the take-away that it might be worthwhile putting a fan on the cat area. Perhaps LTB simply meant that knowing what he does about the stove layout, he doesn't think cooling the skin would cool the cat much, and if so I take his point. I heeded your urging primarily in hopes that someone, myself included, finds it somewhat enlightening and entertaining. I'm often wrong, and apologize if this seems irrelevant or annoying.

 

[SolarAndWood]

Perhaps LTB simply meant that knowing what he does about the stove layout, he doesn't think cooling the skin would cool the cat much, and if so I take his point.

My background is not thermodynamics so my understanding is at the black box level. The tstat's job is to keep the stove at a constant temp. It is a "simple" mechanical control that responds to changes in stove temp by adjusting the air.

The stove top on top of the cat enclosure is by far the hottest point of the stove. It is also where the blower deck goes across, further across on the Ultra than the other models. After I get to a steady state burn, it does not matter if the blowers are on or off, the cat thermometer will read the same. In fact, when I go from blowers full on to blowers full off, the tstat will adjust the airflow and get back to the same point on the cat thermometer within 30-40 seconds. It does not matter if I am going from on to off or off to on with the blowers, the tstat makes the adjustment that fast.

The stove maintains the same temperature, more heat is being pumped into the room. I have found repeatedly that a full load that would normally burn in 24 hours at a given tstat setting with the blowers off will burn in 16 hours with the blowers on at the same tstat setting. My burn time reduces by about a third with the blowers on and I guarantee you the heat is not going up the stack.

This is what I find puzzling about what Beetle Kill and fdegree are seeing with the blowers saving the cat from overheating. In a steady state, it should not make a difference. Let us know what you hear from BK Beetle Kill, I am very curious.


That blanket move is perfect. We have a piece of 2 inch foam across the bottom of the stairs leading to the upstairs of the camp. Without it, we would never be able to heat it up with the stove even though the smoke dragon up there can put out an amazing amount of heat in a short period of time.

 

[Mcbride]

Perhaps LTB simply meant that knowing what he does about the stove layout, he doesn't think cooling the skin would cool the cat much, and if so I take his point.

My background is not thermodynamics so my understanding is at the black box level. The tstat's job is to keep the stove at a constant temp. It is a "simple" mechanical control that responds to changes in stove temp by adjusting the air.

The stove top on top of the cat enclosure is by far the hottest point of the stove. It is also where the blower deck goes across, further across on the Ultra than the other models. After I get to a steady state burn, it does not matter if the blowers are on or off, the cat thermometer will read the same. In fact, when I go from blowers full on to blowers full off, the tstat will adjust the airflow and get back to the same point on the cat thermometer within 30-40 seconds. It does not matter if I am going from on to off or off to on with the blowers, the tstat makes the adjustment that fast.

The stove maintains the same temperature, more heat is being pumped into the room. I have found repeatedly that a full load that would normally burn in 24 hours at a given tstat setting with the blowers off will burn in 16 hours with the blowers on at the same tstat setting. My burn time reduces by about a third with the blowers on and I guarantee you the heat is not going up the stack.

This is what I find puzzling about what Beetle Kill and fdegree are seeing with the blowers saving the cat from overheating. In a steady state, it should not make a difference. Let us know what you hear from BK Beetle Kill, I am very curious.


That blanket move is perfect. We have a piece of 2 inch foam across the bottom of the stairs leading to the upstairs of the camp. Without it, we would never be able to heat it up with the stove even though the smoke dragon up there can put out an amazing amount of heat in a short period of time.

+1.

I get more heat off the stove into the house with fans on, but my stove temp itself remains the same.
Only time I can get too high of temps is if I load the stove up early, say its still 1/4 to 1/2 full of wood and burning well, I open the air intake full, open bypss , then fill full of wood, close dor, turn bypss off, and do not damper down the thermostat righ away, just leaving it wide open, it can max out temps easily.
So if i reload early, i instantly turn the damper down to normal burn range.

Makes me wonder if the OP has a faulty gauge.

Only thing I do differently than I think some others do here, is I tend to split my wood larger than I think most do.
I base this entirely on photos of wood piles and such.
Many her esplit their wood dow smaller than my average piece size.

I burn a wide variety of wood, from pine and spruce, to birch and fir, and even some cedar.

 

[fdegree]

I just got home from work and performed the $ test all the way around the door. There seems to be a very tight seal...the $ never moved when I pulled on it, and even seemed like it might rip if pulled any harder.

Last night I loaded the stove full...bypass open & t'stat on 3.5. This time I did not wait as long as usual to close the bypass and reduce the t'stat setting...once I saw flames starting to come from the bottom layer of the fresh load, I backed the t'stat to 2.0 - 2.25...once the cat thermometer reached 500 I closed the bypass. The cat temp slowly increased...I turned the fans on low once the cat temp reached 1600 - 1700. I had to keep the fans, even 3 hours later, to prevent the cat temp from going to high...I actually kept the fans on all night because I was tired and went to bed. This morning the cat temp was 1000, so turned the fans off...the cat temp increased to 1500 in a matter of seconds...I left the fans off...the cat temp slowly dropped to about 1000 over the course of 1 hour. It kept the house at 71 all night and all day today at that t'stat setting. There is enough fuel left in the stove to last another 3 - 4 hours, making this load last at least 24 hours total.

 

[fdegree]

Just another thought...maybe we have different ideas as to what is considered overheating, when talking about the cat temp.

The stock blaze king thermometer does not have a temperature scale on it, but it does have graduated marks along the outside of the dial. Starting at about th 8 o'clock position and working clockwise...comparing these marks to the thermometer with the numbered scale:
first mark is < 100*
second mark is 500*
third mark is 1000*
fourth mark is 1500*
last mark is 2000*

At 1700* and above, the numbered thermometer indicates this is too hot. So, I have been running the fans in order to avoid this area on the thermometer. But, the stock blaze king thermometer does not indicate this is too hot. I have never reached that 2000* mark, so I'm not sure if the cat temp would settle out before going over that...thus not requiring the fans to keep it under control. Perhaps I'm worrying about nothing and don't need to run the fans when the cat temperature gets in that "too hot" range. SolarAndWood, do you ever see cat temps in that "too hot" range? If so, what do you do?

 

[Renovation]

My background is not thermodynamics so my understanding is at the black box level.

And that is certainly more useful than my theoretical side tracks.

Out of curiosity, I wonder if the layout is such that air could be blown to cool off the cat area more than the thermostat, but that's just idle curiosity.

I share your strong interest in what BK has to say about this. They should have excellent theoretical and applied understanding.

Good luck to BK and FD!