2017-18 Blaze King Performance Thread (Everything BK)
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jetsam
Minister of Fire
The outside air kit did two big things for me. 1 It stopped the constant cold breeze from under the front door. 2 When my wife starts the kitchen exhaust fan ie does not suck smoke out of the stove. No negative effect that I have noticed.
Condensation and even frost on the bare metal outside air pipe is possible in your climate when it is extremely cold. Some folks have insulated the metal intake pipe to eliminate this. I would rather the cold air go right into the stove and up the stack than being sucked in through every crack and drafting across my floor towards the stove to replace the warm air being sucked into the stove's intakes. Also consider humidity control as the outside air is very dry in the winter so feeding the stove outside air directly maintains humidity levels in the home better too.
Don't just put a hole in the wall. You may as well just open a window. Instead, you directly connect the stove to the outdoors with a pipe. I thought it was required in Canada as it is in my location to do this.
Here's my BK hooked up to the intake duct. It never sweats.
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BKVP
Minister of Fire
For areas with heavy snowfall, keep in mind the air inlet has to be kept clear. More than once someone with a wall exit FA has called to say their their stove was burning sluggishly...cleared the snow away and the stove went back to great performance. Think of a dog house type cover, like many dryer vents.
When planning the OSA kit install, I tried to figure out what side of the house had the prevailing wind. After a little research, it was found to be always changing so I plumbed it to under the house where air pressure is neutral no matter the wind direction. The snow problem went away too.
If you use a dryer vent terminus, don't forget to remove the flapper.
If you use a dryer vent terminus, don't forget to remove the flapper.
jetsam
Minister of Fire
I found exactly that issue when my dad bought a new place, and asked me to look at a noise produced by his gas fireplace even when it was off.
The outside air intake was hooked to a dryer vent complete with a nice gasketed flapper, and the noise was the stack's draft pulling warm house air in through the glass doors all year.
Yes and that flexible metal pipe is also very easy to smash if you have kids, dogs, kids playing with dogs, or a wife that likes to clean dust from behind the stove! It never looks right when you try to repair flex. That's why when I rebuilt my hearth I made the non-replacable part of my outside air duct out of rigid 4" HVAC duct. It's cheap and easy to work with.
I've had the unpleasant experience of opening the stove door to light a fire while the range hood was on for cooking. It's just a normal one built into a microwave. The range hood actually was sucking stinky air down the chimney flue and into the house. Shut off the range hood, all was normal and I could light the fire. Then once I was able to close the stove's door I could restart the range hood. If not for my outside air connection, I might have either not been able to start a fire or worse I could have actually filled my house with smoke!
And this is in a 1963 low budget built house that is not "tight".
At least with the OSA the stove can be run after startup. My 1963 low budget house has 2X4 rafters and was,originally, sitting on brick blocks. The builder got away with the cheesy roof because the house pre-dates the building department. It came with a wood stove when we moved in in '71.
oldbluedeer
New Member
Here's a summary of how this resolved. BKVP spent some time giving me some pointers and asking the right questions. Bottom line is that my stove has a 14' chimney with two 45 bends to offset around a ceiling joist. Given this, the rather warm outside temps right now (low 40s overnight), the fuel moisture (12-15%), this results in a slightly insufficient draft for the stove. This raises the lowest tstat setting that I can use to keep the cat in the active zone to about 3-3:30pm on the tstat dial. So the immediate solution is to keep the tstat level at or above that setting, and see what changes after we get into the colder weather. The draft might improve enough with the colder outside temperatures. Otherwise I will need to add some chimney pipe above the roof until I am at the recommended 15' (or 1-2 feet above that to make up for the 45 degree bends).
All in all, I am relieved knowing that I am not damaging the stove. See how it goes...
If it is possible to add the pipe on now, you will get to enjoy the famous BK ultra low burn. That crazy low burn (< 200F stove top) always amazes me.
oldbluedeer
New Member
I am still trying to understand how the tstat damper interacts with the draft in the chimney.
Does the damper restrict cool air going into the stove, or hot air that is exiting the cat on its way toward the chimney?
Also, where do you place the stovetop thermometer? I have the Sirocco with convection deck add-on, so there isn't much free space on the stove top that isn't (1) covered by the convection deck or (2) directly above the glowing cat. About the only other place available is very close to the front on either corner.
The thermostatic air control regulates the incoming air to the firebox. With the convection deck top it the stove top temp is not going to be too meaningful. Go by the cat temp.
Ashful
Minister of Fire
The garbage can, or if you’re more frugal, eBay. No need for stovetop thermometer on a BK, drive by the cat probe.
oldbluedeer
New Member
Thanks for the information.
So here is the part that I don't understand: The tstat damper influences the amount of fresh air coming into the stove by reducing or increasing the effective size of the inlet. The chimney length influences the amount of fresh air coming into the stove by providing more or less draft effectively pulling the fresh air into the stove. I can see how the slightly insufficient draft on my stove could reduce the maximum temperature/burn by the cat with the tstat knob set at highest setting, because in that scenario the chimney draft would be the factor limiting fresh air into the stove. But at lower cat temperatures, it seems like a slightly insufficient draft or a lowering of the tstat knob setting would have the same effect - to reduce the amount of fresh air coming into the stove and thus the temperature/burn by the cat.
In other words, given the same amount of dry fuel, what matters to the cat is the amount of fresh air coming into the stove. And at the low end, a slightly insufficient chimney draft would have the same effect as lowering the setting on the tstat knob.
So then, how is a higher chimney with a little more draft going to enable the cat to burn better at lower temperatures?
With my newly installed Sirocco loaded with hardwood I got a good 24 hour burn, with the stovetop remaining too hot to touch for 26-27 hours, but most of that burning was done with the tstat knob setting between 2-3pm, and the cat therm reading in the "inactive" zone. I am happy with the length of burn, but I will increase the tstat knob setting so that I don't clog up the cat running it a long time in the active zone. I have yet to see what kind of burn I get if I raise the tstat knob setting above 3pm to keep the cat therm in the active zone. This is why I had the conversation with BKVP, so I could enjoy the stove, but not damage the cat in the process of achieving longer burns.
So here is the part that I don't understand: The tstat damper influences the amount of fresh air coming into the stove by reducing or increasing the effective size of the inlet. The chimney length influences the amount of fresh air coming into the stove by providing more or less draft effectively pulling the fresh air into the stove. I can see how the slightly insufficient draft on my stove could reduce the maximum temperature/burn by the cat with the tstat knob set at highest setting, because in that scenario the chimney draft would be the factor limiting fresh air into the stove. But at lower cat temperatures, it seems like a slightly insufficient draft or a lowering of the tstat knob setting would have the same effect - to reduce the amount of fresh air coming into the stove and thus the temperature/burn by the cat.
In other words, given the same amount of dry fuel, what matters to the cat is the amount of fresh air coming into the stove. And at the low end, a slightly insufficient chimney draft would have the same effect as lowering the setting on the tstat knob.
So then, how is a higher chimney with a little more draft going to enable the cat to burn better at lower temperatures?
With my newly installed Sirocco loaded with hardwood I got a good 24 hour burn, with the stovetop remaining too hot to touch for 26-27 hours, but most of that burning was done with the tstat knob setting between 2-3pm, and the cat therm reading in the "inactive" zone. I am happy with the length of burn, but I will increase the tstat knob setting so that I don't clog up the cat running it a long time in the active zone. I have yet to see what kind of burn I get if I raise the tstat knob setting above 3pm to keep the cat therm in the active zone. This is why I had the conversation with BKVP, so I could enjoy the stove, but not damage the cat in the process of achieving longer burns.
jetsam
Minister of Fire
That's a great question and I'd like to hear it answered.
I agree it doesn't make sense, but the guys here convinced me to try, and I was able to burn lower and slower after adding stack height. It also helped with smoke coming into the house (whoch does make sense).
Also, don't conflate "damage the cat" with "clog the cat". A clogged cat can be fixed in 5 minutes with a paintbrush and a shop vac. A damaged cat has usually either suffered physical abuse or (for ceramic ones) repeated thermal shock.
I agree it doesn't make sense, but the guys here convinced me to try, and I was able to burn lower and slower after adding stack height. It also helped with smoke coming into the house (whoch does make sense).
Also, don't conflate "damage the cat" with "clog the cat". A clogged cat can be fixed in 5 minutes with a paintbrush and a shop vac. A damaged cat has usually either suffered physical abuse or (for ceramic ones) repeated thermal shock.
At low burn a point is reached where the thermostatic control looses effectiveness in holding the setpoint temperature. The draw becomes so weak the difference between the setpoint temperature and the actual temperature widens, so control is lost. Also, at very low burn rates the draw becomes insufficient to support continuing combustion. An increased flue height (within limits) will improve draw improving the thermostat's ability to control at low burn.
Poindexter
Minister of Fire
What kf6 said, taller stack, improved draft, thetmostat better able to manage low burn rate.
I ran 13" 6" of elbow free stack my first season, stove settled down when ambients were below freezing. Above freezing the stove was a little cantankerous about how low a tstat setting it would tolerate.
I added two feet to the stack once the snow melted off the roof and have never looked back.
I ran 13" 6" of elbow free stack my first season, stove settled down when ambients were below freezing. Above freezing the stove was a little cantankerous about how low a tstat setting it would tolerate.
I added two feet to the stack once the snow melted off the roof and have never looked back.
jetsam
Minister of Fire
I'm no engineer, but I would would imagine that as the thermostat opens the air, pressure remains constant and flow rate increases. Pressure then increases as the firebox heats up and creates more draw, but the heat also causes the the thermostat to close the flapper back down. Since pressure doesn't vary with thermostat operation, why does increasing it by adding stack give the thermostat a better low range?
oldbluedeer
New Member
Thanks jetsam for the clarification on clogging vs damaging the cat, and the ability to unclog it.
Poindexter and kf6, I will take what you are saying on faith, as I still don't quite understand it. I'll just go with the idea that having sufficient draft allows the tstat to work better at lower stove temperatures, which I guess means that I will be able to adjust the tstat in order to keep the burn at just barely in the active zone without it drifting down into the inactive zone.
Thanks.
Every stove has a "stall" temperature.. Below a certain temperature the air flow is so weak combustion is no longer supported. Increasing the flue height gives more air flow at the same stall temperature enabling a lower burn temperature.
Make sense?
Make sense?
oldbluedeer
New Member
Well yes, now it does make sense, I think... I can see what you are saying, that when the temperature dips down far enough the draft will fail and the air will stop flowing through the stove and up the chimney. Having a higher flue keeps the draft going longer at lower temperatures.
So a higher flue would help provide more complete combustion in the stove, less charcoal and chunks remaining when the fire is cold because the burning continues longer. But I am still not convinced that a higher flue would keep the cat active longer per se, because it seems like when the cat is active the stove is still some ways above stall temperature...
Anyways, like I said I will take it on faith what you say is true, as I am no expert. I may order an extra 2' section of chimney, and if nothing else it will allow me to better control the fire with the tstat knob, and if the cat stays active longer that will be a bonus.
Thanks!
Unless it will break the bank or is not possible, get a 3' or 4' section. The cost difference is not that much. Operationally, exceeding the minimum is a good thing.
Just remember that you need to add those stupid looking and leak causing roof braces one you exceed 4 or 5 feet of chimney above the roof. I think it's five feet but I'm not sure. And then, it will be that much harder to service the chimney cap when it's way over your head.
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