When to engage/close the bypass

[Hunter8282]

So basically, you want to close the bypass as soon as the gauge is showing the cat is in the active zone correct? On either a cold start or reload.

Regardless of what you do with the thermostat, close they bypass once it's active, and you don't want to have the door cracked open at all once the bypass is closed correct?

Do I have that right?

 

[stoveliker]

All Correct.

 

[stoveliker]

One minor detail, upon a hit reload (i.e. cat still reads active) I do let the box burn a 30 seconds to a minute with the bypass open after the door is closed. This exhausts some of the cold (room ) air that came in upon reloading and provides some heat to the wood before the gases are routed through the cat when one closes the bypass. Possibly better for the cat imo.

 

[Woody Stover]

With the digital thermometer and thermocouple/probe setup that Todd gave me, I burn in the load until the temp gets to about 500 (the temp at which they say catalytic burning begins,) then I close the bypass. The flame heat/smoke is then routed to the cat, and the temp takes off, jumping by 4-6* every couple of seconds. The cat generally will begin glowing at about 900, but that can vary. At that point, you can decided to run with a little flame in the box, or none at all, and the cat will remain active.
The only thing I'd add is that if the cat is still active but you want to add more wood, open the bypass for a couple minutes before opening the door, to avoid thermal shock to the cat. This won't cause a steel cat to crack, as it would a ceramic, but I would still avoid it nonetheless.

 

[stoveliker]

The steel cat (and the ceramic one) also can suffer from cold air by having the oxide coating (onto which the active metal atoms have been deposited) spall off of the (metal or ceramic) substrate.
Possibly even more so on the metal one (thermal expansion differences) - I guess.

 

[Egbert Souse']

With the digital thermometer and thermocouple/probe setup that Todd gave me, I burn in the load until the temp gets to about 500 (the temp at which they say catalytic burning begins,) then I close the bypass. The flame heat/smoke is then routed to the cat, and the temp takes off, jumping by 4-6* every couple of seconds. The cat generally will begin glowing at about 900, but that can vary. At that point, you can decided to run with a little flame in the box, or none at all, and the cat will remain active.
The only thing I'd add is that if the cat is still active but you want to add more wood, open the bypass for a couple minutes before opening the door, to avoid thermal shock to the cat. This won't cause a steel cat to crack, as it would a ceramic, but I would still avoid it nonetheless.

I am curious about your thermocouple/probe setup. I'm not thrilled with the catalytic thermometer that Hearthstone provides as the blower tends to influence the reading quite a bit. Any information you can provide me? Thanks in advance.

 

[Tron]

I am curious about your thermocouple/probe setup. I'm not thrilled with the catalytic thermometer that Hearthstone provides as the blower tends to influence the reading quite a bit. Any information you can provide me? Thanks in advance.

You know, I measure every possible metric in my home, but that's one I don't.
Mostly because, as you mentioned, the result is influenced by outside factors, but also because of the very limited information it provides.
If the cat is a bit in the inactive zone when reloading, doesn't matter, it'll get there quickly once the new load catches.

 

[Egbert Souse']

You know, I measure every possible metric in my home, but that's one I don't.
Mostly because, as you mentioned, the result is influenced by outside factors, but also because of the very limited information it provides.
If the cat is a bit in the inactive zone when reloading, doesn't matter, it'll get there quickly once the new load catches.

I'm more interested in the cat temps as I run two key dampers on my stove and there is a narrow band between overdraft and over dampened that I'm trying to replicate more consistently. My blower has a temp probe that I don't love either so I've been looking for retailers that could help me replace both of them.

 

[stoveliker]

but how would you interpret the cat temps in terms of overdraft?

Damping too strong creates more smoke (gases) that are fuel for the cat,so the cat can actually get hotter when you choke the fire. Of course increasing air with a good burn already, leading to a "gates of hell" fire in the stove will also get the cat temps up.

Damping should be looked at with flue probe temps imo, not cat temps.

 

[Egbert Souse']

Damping too strongly/feeding the cat is the metric I'm after. I watch the flue temps closely and I know where i need to there, but getting to that temp without overfire/over damping is a delicate balancing act. The more info I can get to help me the better in my book. I monitor my stove side temp instead of stove top as the blower interferes with that probe as well.

 

[Tron]

Damping too strongly/feeding the cat is the metric I'm after.

I wonder why you don't measure the draft instead? With a motorized damper, you could even regulate it automatically.

 

[Egbert Souse']

I wonder why you don't measure the draft instead? With a motorized damper, you could even regulate it automatically.

Simple answer is ignorance. How does one find a motorized damper? Past that, how would I control it? I've always been jealous of the Blaze King guys' ability to control the air via that thermostat but my issue is draft not air setting. Is there a method to control my damper(s) like that?

 

[stoveliker]

Draft is intimately related to air setting.
When draft goes up, suction on the exhaust of the stove goes up. But how much (primary) air your firebox gets depends on the suction AND the impedance of the total air flow path up to the exhaust port of the stove.
I.e. the air setting "scales" the draft. You can have a draft of 0.2 wc but still choke the fire if your air entrance is as big as a pinhole.

Now if you you also have secondary air, you could restrict the (uncontrolled) input of that too (e.g. with a magnet that you put on as far as you need.

I remain of the opinion that regulating air based on cat temps is not useful or advisable.

I may be misunderstanding things though of what you want.

 

[Egbert Souse']

Draft is intimately related to air setting.
When draft goes up, suction on the exhaust of the stove goes up. But how much (primary) air your firebox gets depends on the suction AND the impedance of the total air flow path up to the exhaust port of the stove.
I.e. the air setting "scales" the draft. You can have a draft of 0.2 wc but still choke the fire if your air entrance is as big as a pinhole.

Now if you you also have secondary air, you could restrict the (uncontrolled) input of that too (e.g. with a magnet that you put on as far as you need.

I remain of the opinion that regulating air based on cat temps is not useful or advisable.

I may be misunderstanding things though of what you want.

When I attempt to restrict air with the air control only, combustion shifts to the secondaries in the top rear of the stove and the stove essentially turns into a blast furnace. Pretty scary. When damping down for an overnight burn, I use the most square splits I have and pack them tightly together. I keep the air control at maybe 35 percent open and use the dampers to slow the draft. Often it's slow to get the balance right as that fire gets going but when settled in it burns slowly with a bit of secondary combustion. By morning I still have some coals and clean glass so that's been working for me. But I'm always open to better solutions.

 

[stoveliker]

I think it may be better to restrict the (otherwise uncontrolled; independent from your primary air handling) secondary air inlet.

 

[Egbert Souse']

I think it may be better to restrict the (otherwise uncontrolled; independent from your primary air handling) secondary air inlet.

Where can I do that? I was under the impression that the primary air inlet doghouse just diverted the air from primary to secondary as you turn the control further down. Closing off some of that secondary air would be lovely. Might be able to get away with a single damper.

 

[stoveliker]

What is the exact stove model you have?

 

[Egbert Souse']

Hearthstone Craftsbury 8392

 

[stoveliker]

I can't see where the air comes in; you'd have to look in the back under the stove is my guess. It's the air flowing through here (hollow piece, blue arrow). There's a secondary air riser in the back that is cut in half in this image.
It likely gets its air from someplace under the stove.

 

[Highbeam]

I wonder why you don't measure the draft instead? With a motorized damper, you could even regulate it automatically.

Wouldn't it be great to be able to use the well proven barometric damper that was built to automatically regulate draft with no electronics or manual input? The wood furnace manufacturers require/recommend them. Would look a little funny in the living room.

Hearthstone Craftsbury 8392

This is the BK forum so maybe there are folks in the hearthstone forum that have solved your problem but I suspect that controlling draft will correct the issues. You measure draft with another gauge and regulate it with some sort of flue damper. Nobody likes a runaway stove.

 

[Egbert Souse']

Wouldn't it be great to be able to use the well proven barometric damper that was built to automatically regulate draft with no electronics or manual input? The wood furnace manufacturers require/recommend them. Would look a little funny in the living room.



This is the BK forum so maybe there are folks in the hearthstone forum that have solved your problem but I suspect that controlling draft will correct the issues. You measure draft with another gauge and regulate it with some sort of flue damper. Nobody likes a runaway stove.

I've read that barometric dampers cool the chimney and cause creosote to form. I have two key dampers to slow draft. I was interested in the cat probe mentioned above to monitor cat temps during my damping process.

 

[Highbeam]

I've read that barometric dampers cool the chimney and cause creosote to form. I have two key dampers to slow draft. I was interested in the cat probe mentioned above to monitor cat temps during my damping process.

Cat temps aren’t directly related to draft. I don’t think it’s a good idea to use cat temperatures as a basis for setting your draft. Instead, use a draft gauge.

 

[Tron]

How does one find a motorized damper?

I just noticed that it doesn't need to be motorized, there are automatic barometric dampers like @Highbeam mentioned. I don't get his comment about the living room, though.

And why do you think that it would cool the flue and cause creosote buildup?
Of course, any damper, be it automatic or manual would need some cleaning now and then.

 

[stoveliker]

Because barometric damper mix in cool room air into the exhaust...

 

[Tron]

Because barometric damper mix in cool room air into the exhaust...

I'm really not familiar with these.
I thought about a damper that controls flue diameter based on draft pressure.
But I'm quiet now ;-)