When to turn down the air?

[begreen]

As a multitasker I can get distracted, especially when taking a dive into a thread solving another problem on Hearth.com.

 

[bholler]

As a multitasker I can get distracted, especially when taking a dive into a thread solving another problem on Hearth.com.

I have 2 young kids and a buisness phone i can get sidetracked pretty easily. That is the main reason i got the auber. So i could set a high temp alarm.

 

[begreen]

I may be doing the same

 

[FPX Dude]

You're the best, or greatest should I say, or yepper even GOAT!

 

[clipse270]

is There any benefit to pulling the air control back as the fire starts to smolder prior to reloading? Or just leave it closed off the whole time until reload?

 

[bholler]

is There any benefit to pulling the air control back as the fire starts to smolder prior to reloading? Or just leave it closed off the whole time until reload?

Opening it up some will give you more heat from the coals and help burn them down faster. But i rarely bothered with it.

 

[Ryan723]

I happened to turn down my air a little too low on my BK Ashford 30 after ~25 minutes of my usual 3/4 throttle setting on a hot reload tonight. Thought i'd share the results (plot attached as in image) as it seems to fit with the theme of this thread.

This wood came from my dwindling 'shoulder season' pile and must have had damper & punkier one than i realized (at least for this air setting on this tired cat...replacement on order).

If i let it go a little longer, I'm sure it would have cooled a little more and the thermostatic air control on the BK would have opened up and fired it off. But I don't like it smoldering, so as soon as I saw it, I opened the air control for ~90 seconds (the jump just after 23:45 tonight in the data plot below). That brought on flames in the firebox and the cat immediately rose and re-lit off. I then dropped the air back down and the cat continued to rise while the flue temps started to fall.

The interesting thing is how relatively steady the flue temps were during the cat stall. Without the cat stall, flue temps would typically drop to about that level as I dial the air back, so flue temp alone might not have tipped me off to dropping the air too low.

Anyways, this just happened and seemed appropriate to this thread.

Some other stats: tired cat with a replacement on order, so the stall is probably worse than others would expect to see with a fresher cat. Flue probe has the tip in the middle of the pipe and located ~28" above the stove top. Catalyst probe is a thermocouple in the usual BK cat probe spot. Stovetop sensor is a thermocouple on the stovetop under the Ashford's convection deck.




View attachment 233113

 

[Jan Pijpelink]

I have 2 young kids and a buisness phone i can get sidetracked pretty easily. That is the main reason i got the auber. So i could set a high temp alarm.

To avoid distractions, we don't have kids.

 

[Mike.O]

I happened to turn down my air a little too low on my BK Ashford 30 after ~25 minutes of my usual 3/4 throttle setting on a hot reload tonight. Thought i'd share the results (plot attached as in image) as it seems to fit with the theme of this thread.

This wood came from my dwindling 'shoulder season' pile and must have had damper & punkier one than i realized (at least for this air setting on this tired cat...replacement on order).

If i let it go a little longer, I'm sure it would have cooled a little more and the thermostatic air control on the BK would have opened up and fired it off. But I don't like it smoldering, so as soon as I saw it, I opened the air control for ~90 seconds (the jump just after 23:45 tonight in the data plot below). That brought on flames in the firebox and the cat immediately rose and re-lit off. I then dropped the air back down and the cat continued to rise while the flue temps started to fall.

The interesting thing is how relatively steady the flue temps were during the cat stall. Without the cat stall, flue temps would typically drop to about that level as I dial the air back, so flue temp alone might not have tipped me off to dropping the air too low.

Anyways, this just happened and seemed appropriate to this thread.

Some other stats: tired cat with a replacement on order, so the stall is probably worse than others would expect to see with a fresher cat. Flue probe has the tip in the middle of the pipe and located ~28" above the stove top. Catalyst probe is a thermocouple in the usual BK cat probe spot. Stovetop sensor is a thermocouple on the stovetop under the Ashford's convection deck.




View attachment 233113

That monitoring is great. Do you have details on it? I would be very interested in something like that.

I assume some sort of WiFi thermometers and an app?

 

[EatenByLimestone]

I always found it frustrating watching the volatiles go up the flue while trying to heat up the stove. Thats a lot of energy thats only warming the flue!

I did a few things to try to catch them. The most important is a top down fire. If the top is the only thing burning, the lower split's volitiles arent released yet.

Above the splits and firestarter, I cram in paper.the goal of the crammed in paper is to raise the temp of the top of the firebox as quickly as possible. The hotter it is, the quicker the secondaries will light off.

Once I light the fire I watch for the fire to start licking the top of the firebox. Once it's reliably doing this I start tapping the damper down.

My goal is to get the damper down to its minimum as quick as possible with a healthy fire and secondaries blazing. Sometimes the stove isn't that hot yet when the damper finishes closing, But the heat is trapped in there. The temp will rise.

 

[Ryan723]

That monitoring is great. Do you have details on it? I would be very interested in something like that.
I assume some sort of WiFi thermometers and an app?

Thanks! It is a homemade setup. I wanted something with wifi logging, smartphone accessible web (cloud) data and charting, and a remote hardware display. I put a rough post about it here: https://www.hearth.com/talk/threads...h-wifi-remote-display-and-datalogging.170402/ I got my stack temperature probe added since that post--i should add to that one at some point.

I couldn't find it, so i built it! it isn't perfect, but i like to tinker. But if there was something similar commercial, i'd be interested too!

 

[Mike.O]

Thanks! It is a homemade setup. I wanted something with wifi logging, smartphone accessible web (cloud) data and charting, and a remote hardware display. I put a rough post about it here: https://www.hearth.com/talk/threads...h-wifi-remote-display-and-datalogging.170402/ I got my stack temperature probe added since that post--i should add to that one at some point.

I couldn't find it, so i built it! it isn't perfect, but i like to tinker. But if there was something similar commercial, i'd be interested too!

Really nice setup and detailed write up. It's way beyond my capabilities to build something like that. Great job.

I would definitely consider purchasing something like that if it came to market. That would be great to be able to monitor how the stove runs all day while at work.

 

[begreen]

Wow @begreen, you surprised me, even the experts gotta watch what's going on, glad you got it.

Yes, every fire is different. This morning I loaded up the stove from a cold start. I was sitting in the living room having a cuppa while the stove warmed up. After about 10 minutes the fire did not look particularly robust yet but I started smelling hot paint. I checked the flue temp and it was already 800F so I turned down the air all the way and the flue temp came down after a minute. What had happened was the fire was burning robustly, but in the back of the firebox, not in the front, so it was less visible, but getting hot. The stove top at the time was only 275º. Not a big deal, but it shows the importance of checking instruments.

The stove has settle in now with a 700º stove top and 580º flue temp. I'm thinking of putting an Auber setup on the stove if I can make it look a bit more attractive and not like a science experiment. I also like what Ryan723 has been working on. Having a cell phone display would be sweet and he's been working on attractifying the setup.

 

[DBoon]

I have a two different stoves - a Lopi Answer (1.6 cu ft firebox, maybe a 15 foot chimney) in my village house and a Lopi Republic (2.2 cu ft firebox, 25 foot chimney) in a house I am remodeling. Both chimneys are straight up.

When new to burning with wetter wood, I had to go to 500 degrees before pulling back 25% on the primary air. Now, I can start at 350 or so in the village house. I have to be patient and do it in 25% increments. I also listen for the telltale clicks that tell me I overdid it and need to give it back some air.

The other house with with bigger firebox and taller chimney is a different story. That stove will rocket quickly to very high temperatures. I don't start earlier, but I am more aggressive in turning it down - 50% on first primary air reduction at 400 degrees or so. Even then, it could just continue to go much higher (750 stove top) if I am not diligent and quick.

I use my phone timer to remind myself when to check. It's saved me more than once.

 

[Easy Livin’ 3000]

I've noticed many people report that their typical startup procedure with a cold stove is to wait until the stove top temperature reaches 500ºF before beginning to turn down the air. That might work for a small, thin shelled steel stove that reacts quickly to temperature change. but it can be much too late for a stove with a lot of mass to heat up. In today's modern stoves the firebox is often insulated to help the fire get up to temperature as quickly as possible so that secondary combustion and clean burning commence. If the wood is dry the fire can have robust secondary combustion long before the stove top reaches 500º. It's better to use your eyes or a flue thermometer to determine when to start closing down the air, than relying on stove top temp. Turning down the air earlier reduces stress on the stove and on the flue system and it can extend burn time.

Flue temperatures are read with a surface thermometer on single-wall stove pipe or a probe thermometer on double-wall stove pipe. A good point to start turning down the air is about 300º on a surface thermometer and 500º on a probe thermometer. A probe will be a bit more accurate as the probe is directly in the hot flue gas stream. You will need your eyes to determine how quickly to turn down the air and how much. This will depend on several factors like how dry the wood is, the thickness of the splits, the species of wood and the strength of the draft. A good starting point is a 50% reduction with the air control half closed. If the fire gets lazy at this point, then wait a few minutes to let it regain strength. If the fire is still burning very strongly, reduce the air another 50% down to 25% (1/4) open. If the fire is very weak or smoldering then open up the air control until the fire regains strength, then try closing down the air again in 5-10 min..

Examples:
As noted, the setting for the air control will vary, but with dry wood and large splits on a cold start I would typically be starting to turn down the air on the Jotul Castine (F400) with a probe flue temp of 500º even though the stove top temperature was only 350º. From that point the air was turned down incrementally over the next 10-15 minutes. After about 40 minutes the stove top would finally be at 500º.

This morning I reloaded the Alderlea T6 on some hot coals. The is a heavy stove with a lot of mass. The stove top temp was 225º. The doug fir pieces I loaded were on the small side and ignited quickly. I returned to Hearth.com, typing up this posting and went a few minutes past when the timer went off. When I got to the stove there was a big ball of flames inside. The flue temp was at 1000º! and I could smell the paint baking. I turned down the air all the way and the fire settled down quickly. At this point, the stove top temp was only 285º. Had I waited until the stove top reached 500º I would have definitely overfired the stove and seriously stressed the flue system, not to mention wasting a lot of fuel. The stove top did reach 500º about 20 minutes later.

As one can see, with a secondary combustion stove, flue temperatures are more helpful than stove top temperatures. I mostly go by flue temperatures alone for guidance and by the look of the fire. For us, the stove top temperature is only relevant for avoid overfiring and if we are going to be cooking on the stove top. This guidance is for non-cat stoves. For a catalytic stove follow the manufacturer's guidance. A catalytic thermometer is a good guide for when to close the bypass and regulate the air.

Excellent post, bgreen. I was doing this regularly the first two years, and I'd catch the liner glowing.

Eventually, I thought, man, I am pissing a lot of heat up the chimney, so, I started to close down a lot sooner, real gradual-like.

Feels like we are capturing more heat from the fires in the house now, fires are lasting longer, and no more glowing liner.