Key Damper Theory

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30WCF

Minister of Fire
Aug 31, 2016
880
North Carolina
It seems the idea behind a damper is to slow the air flow and cool the stove, or keep a stove slow by restricting air before it gets hot. I generally don’t need one on my stove, but have one. Today is the third time I used the damper. I installed it thinking I could slow down a hot fire. However, it seems to do the reverse on a fire that’s getting a little sporty for my tastes.
If I have a fire that’s getting into the mid 600s in the flue, and over 700 STT, I start to watch that one a little closer.

Today I had one that was cruising right along at a pretty good clip.
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This was the reload. What happened was it got going good enough that it consumed the coals and ashes, and as the coals eroded from the center, it took with it the bottom half of the center log. As the bottom row of logs rolled inwards and locked together forming a makeshift arch, effectively holding itself above the fire brick. The end logs had compressed ashes under the extreme edges, and had a hollow trough down the center. I could look under the burning logs and see clear to the back of the stove.

I could have knocked them down, but what’s the fun in that.

I made three attempts to cool it down. First was the key damper.

I shut the damper down to horizontal, and let it ride a few minutes. The temp steady started to climb faster than it had been. And just kept going up. I opened the damper, and the stove dropped back down to around 630 flue.

Second I put my hand over the intake (OAK) connection. The flames slowed, the secondaries settled down, and I was steady dropping temps. As soon as I removed my hand, it jumped back to life and the temps started climbing back up until it leveled out around 630 flue, 745 STT.

If you watch this video a couple times. First watch the thermometer respond to my hand on the intake. Watch it again and watch the flames settle then jump back up.


I tried the damper again after the temps had leveled out. I closed the damper and the STT went from 745 to 825. I opened the damper and it all fell back to low 600s flue/750 STT. A couple minutes later the arch collapsed and we settled in.

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Is this much the same as I hear the cat guys saying to close the air down sooner if folks are having hot stoves. Once it’s hot, shutting down the air/damper won’t really help. If I had shut it down earlier, maybe
It wouldn’t have gassed off that fast. It’s just normally, I dont need to touch anything. My stove doesn’t have controls at all. I added the damper for an emergency brake. Seems like it doesn’t work as that though if it’s already decided to take off. I’ve tried it on three separate occasions. If it’s hot enough I want to slow it down, the damper just makes it hotter.

I’ll be looking for a 3.5” attachment for a damper for the intake. I’ve seen several, but I’m not sure the key damper acts as a brake on something that’s already too hot.
 
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I'm not familiar with your stove but what do you mean by this? Isn't there an intake primary air control?
Aspen C3. “Set it and forget it”
Over all it’s great, and I knew why it was hot, could have stopped it at any time, so I wasn’t really worried.

It has no user controls. There is an automatic damper that is controlled by a bi-metal spring. It actually works fairly well…As long as you don’t get the wood too exposed.
 
I'll have to look at one if I ever get to the hearth store. I don't understand set it and forget it but you say no controls. What are you setting?
 
I'll have to look at one if I ever get to the hearth store. I don't understand set it and forget it but you say no controls. What are you setting?
Thats a good question. I guess the fuel load? That’s the catch phrase on the advertisement.
I can open the door, I can close the door. I can put big sticks in. I can put little sticks in. There are no user controls to manipulate.
That being said, you can run that stove and control it several ways, but the question is:
Is a damper really an emergency brake, or cruise control meant to be set before your speeding? If it’s an emergency brake, I must be driving on ice.
 
Your splits are small, they will take off and be less controllable. Put 2 or 3 large splits in there that fill more of the box and see how she runs.
 
He did the opposite tonight. There was barely room for the 1 large split.
 
I use my damper to slow it down before it gets going too hard without fully closing my primary air control. Full hardwood load takes me about 1 1/2 hours to really get settled in making little adjustments closing it a little more, then opening a little more, then closing again a little more, etc until I can get the flue temp to settle between 700 & 720 and stt 600-620. Damper keeps more of the heat in the stove instead of going up the flue. If I control that top end temperature it makes my cycle much longer.
 
Wow 1.5 hours to dial in? That's an eternity. I get annoyed if it takes longer than 20 minutes.
Yeah, I could probably do it faster if I would char the load more first; but I hate having the energy going up the stack.

Maybe in the name of science I'll experiment more with longer charring and see how long it takes to settle in. Often I'll be at 750 flue, stt rising, and the side pieces of wood are virtually untouched. At some point in shutting down the air or damper (slowly in steps) I'll get a big drop in temperature then it will take off again as the sides take off.
 
Your splits are small, they will take off and be less controllable. Put 2 or 3 large splits in there that fill more of the box and see how she runs.

That load would have been a nice warm load if it hadn't braced itself above the coals when it started eating all the ashes and sending them all up the flue.

It seems the damper is more of a preventative rather than a means for recovering from an over fire. This stove generally runs itself, as the logs crumble.

Normally wouldn’t use the damper at all, and since I don’t mind seeing 700STT, I wouldn’t really think to shut it until it’s too late.

Now, the last few hot fires I’ve had have all been the same issue. Some wood got perched up in the air on something or somehow. That’s an easy fix if you’re there to catch it.

I guess am asking if the only real way to shut it down in a real emergency if the damper is a preventative, is to close off the intake. I can open the door, I can remove wood with my welding gloves, I can consolidate the logs…, but shitting it down has to be at the intake I wonder.
 
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The key damper is more to get the draft back within spec and prevent overdrafting. It will hold more heat in the stove and increase STT as the flue gases can’t escape as easy.
 
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I’ll play with it some when I have smaller fires that I just want more heat out of and see if partially closing it wastes a smaller fire without choking it.
 
I have a typo in post 11, but my window for editing has closed. Seems I get about an hour or two to edit, then the option goes away. Sorry for the potty mouth.
 
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I’ll play with it some when I have smaller fires that I just want more heat out of and see if partially closing it wastes a smaller fire without choking it.
I close the damper less on smaller/shoulder season loads. Any load cruising is at air 1/4 open for me. Anything less and I have charcoal instead of coals and dirty glass in the morning. Full hardwood load cruising is at damper 75-90% closed, smaller & shoulder season loads is damper 50% closed to fully open.

I charred a little longer before shutting the air & damper down last night and was walking away after an hour, so it helped; but I had a little more buildup on the glass this morning. Not a lot, just a little tan on the sides that will burn off in the next fire. Probably means I should char even longer. As a side note (and not to derail the thread), I usually am not reloading on a super bed of coals unless it's really cold out, which I haven't seen yet this season. Lots of reloads on flue temps of 150-200 and stt 100-150 after firing the coals back up.
 
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From what you say about buildup on the glass it sounds like you have some not so seasoned wood. Would also explain why it takes so long to settle in.
 
Most of my reloads are on about 150-200 STT and flue, for me that can be a nice bed of coals still, since my bimetal auto air control opens slower that if I was running it manually.

This morning I had coals I dug out of the ashes from a big log I put in before bed. This is the load last night. It was 180 glue this morning and I stored the coals back to the top and let them burn off. It climbed a tad once they were consolidated.

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From what you say about buildup on the glass it sounds like you have some not so seasoned wood. Would also explain why it takes so long to settle in.
Don't think so... more of a choke the air back a little too far and losing the temperature required for good secondaries when the bottom layer gets buried in ashes and isn't completely burned and I'm in bed. I don't get a lot of buildup or black creasote, just a little light tan on the glass occasionally. Haven't cleaned the glass in 3 or 4 weeks. The tan on the edges will quickly burn off when I reload. This is a NC30 tube stove loaded at 11:00 last night. 11 1/2 hours later and still have pretty decent coals, so I'm stretching it... I don't get the tan every load, just occasionally. Maybe I will play with charring a little more yet or cruising at a slightly higher flue temp to start.

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12-14% 2 summer seasoned aspen, pine & box elder; 14-16% 2 summer seasoned ash, elm & cherry; 14-18% 3 summer seasoned sugar maple, honey locust & hickory; 16-18% 2 summer seasoned ironwood that was standing dead. Properly tested on room temperature fresh splits on the biggest chunks, stored inside since July/August. As always there may be a few possible outliers.
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Ive got the NC32 the next version of your NC30. I never really have that hazing issue. Although I can attest to it sometimes taking awhile for things to get going, the majority of the time I can get it settled within 30 minutes.

Our Englanders don’t seem to want to run low and slow they really like to burn at a decent rate to get it burning the cleanest.
 
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Aspen C3. “Set it and forget it”
Over all it’s great, and I knew why it was hot, could have stopped it at any time, so I wasn’t really worried.

It has no user controls. There is an automatic damper that is controlled by a bi-metal spring. It actually works fairly well…As long as you don’t get the wood too exposed.
I found the manual for your stove and I see there is no manual control for the intake air. Using a key damper would seem to make the firebox hotter therefore closing the automatic air control. Kind of a push me pull you thing where one works against the other. I've never used a stove with no manual air control don't think I want one.
 
Ive got the NC32 the next version of your NC30. I never really have that hazing issue. Although I can attest to it sometimes taking awhile for things to get going, the majority of the time I can get it settled within 30 minutes.

Our Englanders don’t seem to want to run low and slow they really like to burn at a decent rate to get it burning the cleanest.
Yes, they like to run hot. I try to temper that to extend the burn and keep the expensive electric heat from kicking in overnight. Overall I would say it's been successful and even more so with the damper.

Some of the longer tenured members here with the NC30 have told me they hit 850 stt every load and could do a full reload every 4-5 hours if they are really cranking it. I wonder what flue temps would be with that stt...? 1000? 1100?
 
Yes, they like to run hot. I try to temper that to extend the burn and keep the expensive electric heat from kicking in overnight. Overall I would say it's been successful and even more so with the damper.

Some of the longer tenured members here with the NC30 have told me they hit 850 stt every load and could do a full reload every 4-5 hours if they are really cranking it. I wonder what flue temps would be with that stt...? 1000? 1100?


I think purposely going that high is nigh on insanity
 
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I found the manual for your stove and I see there is no manual control for the intake air. Using a key damper would seem to make the firebox hotter therefore closing the automatic air control. Kind of a push me pull you thing where one works against the other. I've never used a stove with no manual air control don't think I want one.
By the time the damper would matter, that auto air control is long been closed. But you are correct on the cool down. If it trapped any extra heat, the intake wouldn’t start opening quite fast enough.
 
I close the damper less on smaller/shoulder season loads.
I suppose what I meant by trying it out on smaller fires was, sub 750STT to play around with more.
 
Round 1 at intake damper for slow downs. I’ve seen the blast gate thread, but was gonna try to customize it a bit for my needs.
I think this lets enough air in. I can cover over 50% of the intake with foil when the stove is going, and not affect the flue temps, so I figure I have about 40% of the oversized intake. The actual air intake inside the stove’s OAK connector is only about 5/8”x 2” rectangle, when fully open, and a couple pin holes when fully closed.
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I had a jar lid I kept on the shelf for emergency shut downs, that snapped tightly into the OAK connector to shut the air off.

I found a replacement vent for a grill or smoker on Amazon and cut out the center of the lid and bolted them together.

Its really to hot this morning to get a ripping fire going to verify that fully open lets enough air pass, but it’s supposed to be in the 20s tomorrow. I plan to pop it in and out a few times when the stove is cruising steady and up to temp to see if it lets sufficient air in while the vent is open, or if the Auber takes a dive. If so, I might have a way to shut it down or tame it when the off gassing gets a little sporty at times.

Here are a few pics and a demo video. If it works, I’ll put a couple self tappers in just to secure it in place if there is a back puff or draft reversal. Its pretty tight as is though.

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