Blaze king running too hot?

[bhylton]

Hey all, stove is a bk scirroco 30 with appox. 28ft of vertical pipe. The combustor/stove is on its 3rd full season.
Burning lodgepole and doug fir currently at about 10% moisture.
I started a fire about 3 hours ago and shut it down but the cumbustor temp has continued to climb. No flame on the box for the last 2 hours. I'm concerned it's going to damage the combustor but I can't turn it down an farther... advice? Its just crusing along at these temps

 

[Todd]

Give it more air till you have flame in the box that will take some of the work off the cat. I used to see this in my cat stoves. Sometimes the cat just gets overloaded with smoke. What size splits? Sometimes larger load with large splits burn better than a large load with smaller splits.

 

[bhylton]

Turning the stove up was on my mind for sure... similar to more rpm on a diesel lowering EGTs. I would say the splits are medium, definatly not large. I will try some larger splits next load and see how it goes.

 

[Highbeam]

Your 28' stack is way over the max so you are overdrafting. This really means that the chimney can suck more air into and through the stove than it should be able to on the lowest setting. That and you have extremely volatile fuel. Pretty good for a 3 year old cat!

If you had a key damper, now would be the time to close it and bring back some control. Can you block the intake? It's the square opening in the back bottom. Stuff a rag in there until the cat meter gets back below 1500. You are essentially experiencing a runaway.

Don't worry about damaging the cat, it's really easy to replace and you're cat is probably well used. Worry instead about melting the bypass retainers that are right on the backside of the cat.

 

[bhylton]

Thanks for the info. It would often cruise around 1200 last year, but after heavy creosote buildup last season I went to greater lengths to season wood this year... that must be what's putting it over the edge. I guess I need to add a damper? I don't have any options to change pipe. It's 22ft from the floor to ceiling then another 6ft to clear the roof peak.

 

[bhylton]

Also it seems strange to "overfire" when there is no visible flame haha

 

[Ashful]

At 28 feet, you're likely pulling around 3x the allowable maximum draft for that stove. Install at least one key damper, about eye level. A magnehelic plumbed into the pipe above the damper is also handy, so the many photos posted in the past of my rig.

 

[bhylton]

At 28 feet, you're likely pulling around 3x the allowable maximum draft for that stove. Install at least one key damper, about eye level. A magnehelic plumbed into the pipe above the damper is also handy, so the many photos posted in the past

At 28 feet, you're likely pulling around 3x the allowable maximum draft for that stove. Install at least one key damper, about eye level. A magnehelic plumbed into the pipe above the damper is also handy, so the many photos posted in the past of my rig.

Looking at it right now, it's probably closer to 22-24ft.. regardless it sounds like too much. Interesting though that that last 2 seasons I have not had this issue.
If I shove a towel in the air Intake and see no difference to the flame in the box, I would assume i have an air leak somewhere? My door shuts super tight after adjusting the catch, but I will check that after it cools. Is 2 or 3 Years all you get from a door gasket?

 

[Highbeam]

Looking at it right now, it's probably closer to 22-24ft.. regardless it sounds like too much. Interesting though that that last 2 seasons I have not had this issue.
If I shove a towel in the air Intake and see no difference to the flame in the box, I would assume i have an air leak somewhere? My door shuts super tight after adjusting the catch, but I will check that after it cools. Is 2 or 3 Years all you get from a door gasket?

There is a hole in the intake system that allows a controlled amount of combustion air in even when the thermostatic intake valve is fully closed. That hole will flow a lot more when the chimney is overdrafting.

Also, like me, you have very dry resinous fuel that makes lots of fuel for a catalyst. On low there is no flame to eat the fuel so that cat is working hard. My cat meter runs pretty high when burning at low settings even though my chimney is not very tall.

I wouldn’t want the door to latch “super tight” but just tight enough to make a good seal. Door latches wear too. You should get at least 5 years from a good install of an oem gasket.

 

[Ashful]

Looking at it right now, it's probably closer to 22-24ft.. regardless it sounds like too much. Interesting though that that last 2 seasons I have not had this issue.
If I shove a towel in the air Intake and see no difference to the flame in the box, I would assume i have an air leak somewhere? My door shuts super tight after adjusting the catch, but I will check that after it cools. Is 2 or 3 Years all you get from a door gasket?

Not a surprise. The BK is infinitely-controllable. It'd probably take a chimney through a high-rise building to generate a true stove-overfire situation, but that doesn't mean your efficiency isn't in the toilet, or that you're not plugging cat combustors with all of the fly ash you're likely stirring when running the stove at higher settings with that much pipe.

I ran for a year or two with 30 feet of insulated pipe, wide open. Never had an overfire, but things would get scary in bypass, and I was forever plugging my cat combustors with fly ash. I installed a key damper, and the stove just got so much more pleasant to operate. Also, I'm putting a lot less heat up the pipe now, as evidenced by the flue probe thermometer, assumedly meaning more of it is staying in my house and heating my home.

I would seriously consider a key damper. If you don't want to add a monitor (eg. magnehelic), just open the key damper wide for starting, and then close it about 90% once the flue is heated into the orange. That will probably put you pretty close to the ideal 0.05"WC target. The only trouble in running a key damper without a monitor is that the setting which generates optimal draft will change throughout the season, as creosote builds up on the little bypass holes in the key damper. I start every season closing mine 100%, and still being a bit over-drafted, and end most seasons with only having to close it 80%, as a small ring of creo builds up in the pipe right around the damper.

 

[Ashful]

I thought it might be useful to show how I plumbed mine. Here you can see the relation of flue probe thermometer, key damper, and the magnehelic:



The magnehelic is connected by high-temperature rubber hose to a bit of stainless steel brake line. A small size-matched hole drilled thru the double-wall pipe allows insertion of the brake line into the flue, and it's fastened with a few stainless hose clamps, as shown:



This was all done on the back side of the pipe, to hide it from plain view. All tucked back into a fireplace, it's really quite unnoticeable:



We "drive" the stove by adjusting that key damper to maintain 0.05"WC after the wood catches, and until we eventually turn down to our cruise setting. The readings are only valid when running the stove on a high setting, and will climb as soon as you turn the stove down, due to restriction of the inlet. BK only calls out draft setting at wide open throttle.

PS - I just noticed that it might appear to some that the magnehelic is plumbed into the pipe above the key damper, but that is not the case. Magnehelic feed tube penetrates the pipe well-below the key damper. It is measuring draft presented to the stove, not what you have in the pipe above.

 

[bhylton]

I thought it might be useful to show how I plumbed mine. Here you can see the relation of flue probe thermometer, key damper, and the magnehelic:

View attachment 317391

The magnehelic is connected by high-temperature rubber hose to a bit of stainless steel brake line. A small size-matched hole drilled thru the double-wall pipe allows insertion of the brake line into the flue, and it's fastened with a few stainless hose clamps, as shown:

View attachment 317392

This was all done on the back side of the pipe, to hide it from plain view. All tucked back into a fireplace, it's really quite unnoticeable:

View attachment 317393

We "drive" the stove by adjusting that key damper to maintain 0.05"WC after the wood catches, and until we eventually turn down to our cruise setting. The readings are only valid when running the stove on a high setting, and will climb as soon as you turn the stove down, due to restriction of the inlet. BK only calls out draft setting at wide open throttle.

PS - I just noticed that it might appear to some that the magnehelic is plumbed into the pipe above the key damper, but that is not the case. Magnehelic feed tube penetrates the pipe well-below the key damper. It is measuring draft presented to the stove, not what you have in the pipe above.

Interesting. I think a damper is a good first step. I've thought about it getting one before. During initial start up I always have to close my bypass WAY before the cat is active. Otherwise the flue temp would be like 1500 before the cat warmed up. Figured a damper would help that problem as well. I looked in my manual and it appears that the minimum pipe length for my setup and elevation is 19.5ft. Do you think being at 5 or 6ft more would really put me thar far out of spec? Thanks folks for the detailed responses

 

[Ashful]

Interesting. I think a damper is a good first step. I've thought about it getting one before. During initial start up I always have to close my bypass WAY before the cat is active. Otherwise the flue temp would be like 1500 before the cat warmed up. Figured a damper would help that problem as well.

Yes, I had the same problem, and it definitely helped.

I looked in my manual and it appears that the minimum pipe length for my setup and elevation is 19.5ft. Do you think being at 5 or 6ft more would really put me thar far out of spec?

I think these spec's are somewhat self-conflicting. I know BKVP can't really discuss any recommendation for a key damper, it would violate regulations that prohibit manufacturers from recommending operation that does not conform to the method under which the stove was tested. But based on my own measurements, it really appears any chimney much over their minimum height specs will violate the 0.06"WC absolute maximum spec they put in my manual.

All I can say is that installing the key damper really tamed down my rig, and a few others have done the same with the same conclusion. Until the reg's change, and allow the manufacturer to comment with more detail, I guess that's all we have to go on.

 

[Highbeam]

There's no risk. If the damper is left wide open it is as though it is not there. You can save it for a last ditch safety device during a chimney fire.

 

[Hoytman]

PS - I just noticed that it might appear to some that the magnehelic is plumbed into the pipe above the key damper, but that is not the case. Magnehelic feed tube penetrates the pipe well-below the key damper. It is measuring draft presented to the stove, not what you have in the pipe above.

Obviously from the pictures your gauge is plumbed just like my manometer.

So, in post #7 …

A magnehelic plumbed into the pipe above the damper is also handy…

… were you suggesting to install a second gauge (above the damper), or was that a typo?

Two gauge’s certainly doesn’t hurt anything. Just wanted clarification of what you meant.

By the way, nice looking set-up and extremely nice install of SS mag line. I’ll grade you A+ on that.👍 Really nice job installing and hiding it.

 

[Ashful]

… were you suggesting to install a second gauge (above the damper), or was that a typo?

Two gauge’s certainly doesn’t hurt anything. Just wanted clarification of what you meant.

By the way, nice looking set-up and extremely nice install of SS mag line. I’ll grade you A+ on that.👍 Really nice job installing and hiding it.

The only thing that post is suggesting, is that I need to stop posting advice after a night cap, or after sitting in front of my computer for 17 hours. Both of those factors conspired against me at 11pm yesterday.

yeah, magnehelic or any other manometer should be installed below key damper. Sorry for the confusion.

Here's a side view that shows all of the penetrations, in relation to stove top. In case it's not obvious, the stainless tube that feeds the magnehelic penetrates the stove pipe about 2" above the flue probe thermometer, and about half way between stove collar and key damper.



@begreen, fell free to fix post #7, if you get a chance. My time to edit has expired.

 

[Hoytman]

Be interesting to see the difference in readings above and below the damper on the same pipe.

 

[Ashful]

That's easy enough to simulate by playing the air control on the stove, with the damper open. But to put some numbers on it, with the stove thermostat wide open, I measure around 0.21" to 0.24" water column with an open key damper. Closing the key damper would therefore create numbers higher than this, at least initially, until the pipe cooled.

Do note the pipe changes temperature quite dramatically, both above and below the damper, after closing the damper and allowing time for a new steady-state.

One more thing worth mentioning: with massive overdraft, I suspect it's possible to cause flame impingement damage to the combustor. I can watch flames get literally sucked into either the bypass or combustor, with the damper wide open on my 30 foot chimney. This never happens on my 15 foot chimney (unless I leave in bypasss too long) or with my key damper closed.

 

[Heat Maxx]

I thought it might be useful to show how I plumbed mine. Here you can see the relation of flue probe thermometer, key damper, and the magnehelic:

View attachment 317391

The magnehelic is connected by high-temperature rubber hose to a bit of stainless steel brake line. A small size-matched hole drilled thru the double-wall pipe allows insertion of the brake line into the flue, and it's fastened with a few stainless hose clamps, as shown:

View attachment 317392

This was all done on the back side of the pipe, to hide it from plain view. All tucked back into a fireplace, it's really quite unnoticeable:

View attachment 317393

We "drive" the stove by adjusting that key damper to maintain 0.05"WC after the wood catches, and until we eventually turn down to our cruise setting. The readings are only valid when running the stove on a high setting, and will climb as soon as you turn the stove down, due to restriction of the inlet. BK only calls out draft setting at wide open throttle.

PS - I just noticed that it might appear to some that the magnehelic is plumbed into the pipe above the key damper, but that is not the case. Magnehelic feed tube penetrates the pipe well-below the key damper. It is measuring draft presented to the stove, not what you have in the pipe above.

Beautiful stonework!!

 

[Ashful]

Beautiful stonework!!

Thanks. Those stones up to about the probe thermometer were laid up in 1734, and then continued up from there in 1775. If I ever meet the two masons that did the work, to pass along your compliment, it won't be in this world!

 

[bhylton]

Hello all, wanted to give an update.
While examining my stove, I noticed some chunks of sealant on the floor in back. I traced them back to the thermostat housing. I had removed the thermostat to clean and adjust the tension on the knob and apparently broke the sealant off.
I re installed and sealed the thermostat with red high temp rtv... the stove shuts down tight "airflow" now. And I am able to totally snuff a ripping fire by closing the thermostat. Looks like I have control back, it was just unmetered air sneaking around the thermostat.
I did buy a damper so I may install it anyways. Thanks for all the help everyone. @Ashful and @Highbeam