What does your burn cycle look like?

[FionaD]

hi,

I'm just coming into my second year as a happy, obsessive wood scavenger and burner. I have a Jotul F3 CB which, it turns out, is just the perfect size for my cottage. After spending spring and summer gradually discovering and fixing all the (major) issues of a shockingly inept installation by people who claim to be professionals, I am discovering that my stove experience, as I fire up at the start of this second burning season, feels almost like learning from scratch - this fixed stove burns so differently!. This is All positive - I'm discovering for instance that my stove's burn times for a full load have literally doubled now everything is the way it should have been from the start.

So, related to this new learning curve, I wanted to ask anyone out there,especially those with similar stoves, about their burn cycle...

After adding a new full load, when do you shut off the secondary air and how do you do it? I have so far done it this way -

- open secondary air fully
- load up
- let it roar till it gets to 600
- shut it right down in one go
- then it cruises for a while at 600 with lots of secondaries, and slowly cools over several hours
- In my home situation (size, insulation, outside temps, etc) when I get to a little under 300 and have a flat bed with just a few red coals I consider it the end of the cycle and time to reload.

However.... I am noticing that many of you prefer shutting down the air in 2 or 3 stages from around 450-500 degs onwards... I'd love to know the purpose and/or advantage to that- is there a secret, better performance that I need to know about?

So I'm experimenting with shutting down in stages today.... So I loaded up almost 2 hours ago and shut the air half way back when it was flaming enthusiastically at around 400. Then I left it for about another 10 mins, till it got to around 450, then shut the air down another 1/4... Then closed it right off when it got to 500 and secondaries had appeared. It burned happily, holding on to good secondaries after that.

Two hours later, it seems to be at the same stage in the cycle as I would normally see in my old style of shutting down in one go.

So is there any advantage to my shutting down in stages or is it just about what some stoves need? I will keep experimenting, but so far all I'm noticing is that I'm getting a bit more excercise.

Other than that.... Like I've seen others say here, for the first time ever, I have actually been looking forward to the colder weather arriving here in Scotland... that's a real first for this particular sun worshipper!

 

[Jags]

Personal opinion: I don't think smaller stoves react quite the same as large ones do when using the "staged" shutdowns. Big stoves with a lot of mass can have a temp "whiplash" effect once they really start to roar. Your little jotul, in comparison, is controlling a much smaller fuel load.

It appears that both methods work well for you, but from your results I would conclude that the method is up to you and there probably isn't gonna be any grand change of performance from one to the other. Things change when you are loading up a 3+ cuft stove to the gills that has 500 pounds of mass to deal with. (part of the learning curve for any given stove).

 

[WES999]

- let it

roar

till it gets to 600

I am assuming you mean 600 measured on the stove top.
When talking stove /flue temps it is best to be specific as there are many variables, single wall or double wall pipe, internal external thermometer etc.

I start closing the air in small increments based on flue temp (internal digital thermocouple probe).
I start closing when the flue temp hits 875, with dry wood and kindling this may only take a few minutes.
I keep closing the air to keep the flue temp under 900
Generally the quicker you can close the air without starving the fire the quicker the stove will heat up.

If you are letting the stove top heat up "roar" to 600 you are loosing a lot of heat up the chimney and
may be overheating your flue.

 

[begreen]

There normally isn't any secondary air control on a stove. That is the primary air control. The secondary air is unregulated on most stoves. You'll get longer burn times and better control over the stove by closing the primary air sooner and in increments. On a cold start the stove top temp is usually around 300F when I start turning it down, but it could be as low as 250F. I do it more visually than by temp. As soon as the logs are burning robustly I start turning down the air until the flames start getting lazy. Then I wait a while for the flames to regain robustness. Then I turn down the air again. Repeat if necessary until the air control is about as far closed as it's going to go without smoldering the fire. The number of steps will depend on the wood. I am burning some nice dry doug fir right now that only takes turning it down twice. But for less dry wood it may take 3 reductions.

 

[FionaD]

I just can't get my head around stoves that kind of size and who needs them. But I guess winters are way colder in much of the US. My F3 heats a 17' x 19' living room that's open to a kitchen of the same size. I leave the living room door open and the rest of the house gets the left over heat.. Living room /kitchen averages 70 F and the bedrooms on the far end of the house are several degrees less, which is perfect. Any more heat than that and I'd be melting like a candle.

I wonder if it's also to do with my cottage being stone rather than wood like so many hoise in the States? Maybe the stone walls hold the heat much longer once they're really warmed through.... I have noticed that the stone wall behind the stove is still almost as warm to the touch 12 hrs after the stove has gone out as it is when it's lit.

I guess I'll keep on experimenting a wee bit longer. I have noticed that, now the stove/flue connection is airtight (one of the many issues it had before things got fixed) the stove temp seems to keep on rising after I completely shut down the air. This never used to happen, so I do need to learn shut down around 500 now, rather than 600. I hate it when the stove gets to 650-700, even if only for a little while.

I can't help but notice how few girls there are on this forum... just all these growling, axe-wielding guys. I am imaging you all have big beards! Interesting... Stoves must be a man thing in the US... Maybe that's the case here too and I'm unusual.. Anyway.... ff to stack more wood before its totally dark.

 

[Sprinter]

My take on it is that you should start shutting down the air when the secondaries are burning and the flue temps are above creosote levels. I don't really see any reason to wait longer than that since you're presumably looking for efficiency. On my stove that point is usually with the stove top less than 200F. Then you can keep turning it down in increments, keeping the secondaries hot and a lazy flame.

If you don't have one, you should invest in a flue thermometer as well. If you have the air full up until the top is 500 or more, then the flue may be getting way too hot. But like Jags said, your small stove may act a bit differently than a larger one. In general, though, you'll get better efficiency by getting air turned down when the secondaries are active. Just keep an eye on secondary burning and flue temps.

 

[FionaD]

Thanks WES999 and BeGreen for your poststhat appeared whilst I was still writing.

WES999 - Yes.. 600 F is my stove top temp. I can't really measure my flue temp as the flue exits the back of the stove and goes through a stone wall after about 4 inches and then up a stone chimney.

I will try not to 'roar' so much and aim to start shutting down sooner. I suspect I've been overzealous with the idea that hot burns are the way to go to cut down smoke... And working on the notion (perhaps inaccurate) that I need to get to 600 before shutting down, or I won't get secondary burn.

Sprinter - you get secondary burns when your stove top is less than 200f?! I am getting confused now about flue vs. stove top temps. Especially if 500 plus on the stove top is too to for the flue... My understanding is that this is the ideal operating range for the f3. Oh dear...

BeGreen - sorry - am I misusing air flow terms? I'm talking about incrementally turning down the air flow that is NOT the one only to be used for lighting up the stove. I guess I call it the secondary flow because I associate it with secondary burns.

I am of course interested in getting longer burn times, so i'll keep experimenting, encouraged by your thought that incremental shut downs seem to prolong burns for your stove... Although I appreciate my f3 is not quite the same animal as the 602.

 

[begreen]

The little control on the front is called the startup air control. It's more of a pre-primary control. We had the F3CB several years ago and the burn procedure I described worked well with it. One difference though, I didn't use the startup air control. I just left the door agar slightly on the latch until the fire was starting to burn well, then latched the door.

 

[Elbinwyp]

Big stoves with a lot of mass can have a temp "whiplash" effect once they really start to roar.

Jags. What do you mean by this? I am a first time wood burner trying to figure out the Woodstock IS.

 

[Mellery]

Peeks in to say us girls are here but for me, I typically defer to those with many more years experience than me. I start turning down the air when I see a nice char on the surface of all the wood I can see through the glass.That could be anywhere from 2-15 minutes depending on the coal bed; typically 300-400F or so. With our stove, I never turn it down all the way but always leave it open just a little. Then I open it back up towards the end of the burn to get every last BTU before reloading. I shut down in stages because it burns the wood most efficiently that way; the load produces heat longest. I've heard it referred to here as massaging your stove. I have gotten better at it all and don't even need to check the thermometer any more. The coal bed, flames and char are my indicators.

And I do wield a very sharp axe lol - my husband likes the Fiskar I picked out though : )

Oh, and 3 of my 6 closest neighbors are women that take care of their wood stoves, 1 in her 70's and 1 in her 80's.

 

[Sprinter]

Sprinter - you get secondary burns when your stove top is less than 200f?! I am getting confused now about flue vs. stove top temps. Especially if 500 plus on the stove top is too to for the flue... My understanding is that this is the ideal operating range for the f3. Oh dear...

Well, I'm describing the startup period. Once you've started a new fire, the firebox and secondary system will usually get hot enough for secondaries to burn (above 1100F) way before the stove top has had a chance to get to a cruising temp. If you keep the air fully up much beyond that point, then the flue can easily get too hot.

Once you get the air turned down and the fire is more mature, then the flue and stove top temps stabilize and you're cruising. You don't need for the air to be up high in order for the stove top to get up to operating temperature. It will continue heat up very well once the air is turned down and secondaries are doing their job.

 

[Jags]

Jags. What do you mean by this? I am a first time wood burner trying to figure out the Woodstock IS.

More mass takes longer to respond. Once you start noticing the response it can climb pretty quick if your not paying attention. Of course there are many variables and YMMV.

 

[FionaD]

Thanks Sprinter... I think I get it now. Guess I just can't know about my flue temps given the fact my flue is inside my chimney. I am hearing loud and clear that I can well afford to shut down much sooner than I have been though.

Hi Mellery! Glad I'm not entirely the only axe-wielding girl here... Nothing like releasing the inner Boadicea, Sounds like you're another one who's giving me encouragement to shut down sooner. I've just loaded the stove up and I'm watching carefully for the first signs that I might start shutting down. Stove top is still under 400 and wood not all charred yet. No secondaries showing, but as soon as I see them I'll shut down a tad and see how it goes.

I've learned a lot today.thanks so much everyone.

 

[flamencogirl]

I have a small insert. I find that I need to step down my fire, especially on a cold start. How many steps varies upon the wood and outside temps. With a reload I usually have fewer steps. But rarely do I go from having the air wide open to shut. Even with a roaring fire it will choke. With an insert it is next to impossible to check flue temps (i've used the IR, but an not sure how accurate it is given I can only access the first inch or so of flue). I usually just go by the look of the fire.

Johanna, a mostly lurking female

 

[Sprinter]

No secondaries showing, but as soon as I see them I'll shut down a tad and see how it goes.

You probably won't see much at this stage. When you have a lot of flame and the air up high, there's no light show. Best way is to look at the chimney and wait until the smoke is pretty much gone. Then you know the secondaries are working. After a while, you'll get to where you don't have to do that much anymore, although I still do now and then. When you get the air down pretty far is when you'll really see the secondary action.

 

[Mellery]

There are many of us : ) and with my smaller insert, I don't normally see secondaries until I start shutting down the air. And the temp can really jump up and fast when I do! In the coldest of winter, I do watch the thermometer so I don't over-fire as it can happen pretty quickly with our well-dried, hardwoods especially when I pack it full. (I keep a thermometer on the top of the stove, in the same spot - more for a reference of overall than exacts)

Cheers !!

 

[begreen]

There are many of us : ) and with my smaller insert, I don't normally see secondaries until I start shutting down the air. And the temp can really jump up and fast when I do!

Shutting down the primary air introduces a vacuum in the firebox created by the flue draft. This negative pressure pulls air through the secondary manifold and into the top of the firebox. Secondary combustion is usually more efficient, thus raising the stove temp more quickly.

 

[mass_burner]

I just can't get my head around stoves that kind of size and who needs them. But I guess winters are way colder in much of the US. .

Don't forget a lot of folks from Canada on here too. Yes, colder than in Scotland; also I may be correct in saying that homes tend s to larger in the states, more space to heat. I couldn't grow a beard to save my life, but I do like swingin' the axe.

 

[FionaD]

Hi to Canadians too. I suspect calling a Canadian 'American' has much the same reaction as calling a Scot 'English'.

Well... Just when I think I was getting the hang of my stove I realise I have been getting things quite wrong in some respects. Coupled with the fact that its behaving so differently now it's fixed it is best, I think, for me to regard myself as a complete beginner. It is news ( and new) to me to experience secondary burn as something that causes the stove to get hotter... last season my non-airtight stove started to lose heat as soon as I started to shut down the air and get secondaries. Now it continues to get hotter, but that's obviiusly how it's meant to be, from what you're saying. I feel like I've moved to a different planet.

Well.... My last load went in 2 1/2 hours ago and my attempt at shutting down gradually wasn't that successful. I started to shut down to just above halfway at around 500 stovetop temp. Got some secondaries but also lots of flame from the wood.. I Shut down a little more 10 mins later and the fire started to die back too much.. No flames of any kind. Opened it up a little again and the logs started burning without secondaries. Closed back a little 5 mins later and a few secondaries came, but they almost looked like log flame, if you see what I mean,Mao I want entirely sure they were secondaries. If I closed the stove all the way down it just died every time. Should I have just left it at 3/4 closed with a mix of burning log and some secondaries or did I perhaps need to close down more slowly?

I can't go outside to look at the smoke. It's too dark.

I guess I've become very used to the habit of closing the air right down for the last and longest phase of the cycle and consequently I now think that I must be burning the logs too quickly if the air is left even slightly open after 30 mins. I have read other posts on the form saying some people's stoves never get turned all the way down. So perhaps I shouldnt be concerned about this.

I think I am thinking and fiddling too much now... I can take my time... Tomorrow is another day

 

[begreen]

Modern clean burners don't work like older stoves. The secondary burn cycle is typically where the peak heat occurs in a newer design. The secondary burn period, with good dry wood in the F3CB is not long. There isn't enough fuel for more than about a 30 minute secondary burn. Turn down the air until the flames get lazy, but not out. Then wait, if the fire build back in intensity close down the air some more until the flames get lazy again. If they stay lazy leave the air control there, if the fire builds up again, rinse and repeat.

True, some stoves can not have the air control completely closed due to less draft or damper wood, or very hard wood. You have to judge according to the variables at hand. As it gets colder outside don't be surprised if you are able to close the air control further. Draft increases with colder temps.

 

[FionaD]

That's helpful to hear from someone with past experience of a f3 CB. Thanks. What an eye opener today has been..! I Look forward to putting all this into more practice tomorrow. Almost bed time over here. Night all

 

[Mellery]

Shutting down the primary air introduces a vacuum in the firebox created by the flue draft. This negative pressure pulls air through the secondary manifold and into the top of the firebox. Secondary combustion is usually more efficient, thus raising the stove temp more quickly.

We burned our wood stove the first winter without knowledge of secondary combustion

Revelation struck when I read this: Secondary Combustion is your Primary Heat Source * aha moment * of course I had no idea what that was and thus my discovery of hearth.com : ) and we now use a lot less wood and know how to use the wood as the temperature control.

I tried to find the size of your firebox but couldn't. I do know it's on the small size but your stone cottage and stove seem quite the match.

Happy Heating : )

 

[FionaD]

I'm not sure I could tell you the size of my firebox either... At least not in American sizes all I can tell you is its an EW box and takes max 18" logs.

You must have felt amazing when you got the secondary burn thing at last! I sure had them all year, but too much so, it seems. Now I'm learning all over again...

Well, I've been hard at the experimenting all day, trying to start turning down incrementally and get secondaries at lower temps, (rather than 'roaring up to 600' and shutting off all at once).. I have managed to get secondary burns (whispy flames) after around half an hour into a burn cycle, after lots of fddling l back and forth, up and down, with the air control. I can't seem to get them to kick in at lower than 500 deg (stove top) though - except at start up this morning. The other thing is I'm not getting any ongoing temp increase at all if I start shutting down as soon as I get secondaries... No 'cruising' either, just a slow fall away in temps over the next few hours after between 30-60 mins of whispy flames. I checked the chimney and there was no smoke at any point I reckoned I had secondaries burning, so that's something... I still can't say I've got it right though, as for the first time since getting the stove last year I have occasionally been chilly in the house today - the stove gets to around 500 but falls away very quickly. This may also be because - after reading Brother Bart saying people shouldn't load their stoves right to the top - I've been putting less logs in on the assumption that was something else I was overdoing ...

So all in all, today's fires have been meagre, relatively speaking... The sort Scrooge would approve of.

Any extra wee tweaks anyone can suggest? Only thing I can think of is to let the temp rise a little more before I start to turn down the air... But then I'd be pretty close to the way I used to operate the stove ( going right up to 600 before turning right down)

Worse case scenario is that I have been getting such a warm cottage so far because I was overfiring the stove and flue and, now I'm maybe burning correctly and discoveing I actually need a bigger stove. I don't think that's it though... Instinct tells me I just haven't found what some people here call the sweet spot yet...

I'll keep trying...

 

[Jags]

.. But then I'd be pretty close to the way I used to operate the stove ( going right up to 600 before turning right down)

And it kept you warm
And it was a clean burn
You weren't abusing the stove
It was a pretty painless method to operate the stove...
Ever wonder if you are fixing something that wasn't broke?

 

[FionaD]

Jags... I hope that's true . Guess I've got scared for my stove etc, with the talk about possible over heated flues and overloaded fire boxes.

Maybe a middle way would be for me to aim for my old style of operating but just tweak slightly in favour of turning down sooner, rather than what I seem to have been doing today, which feels like too much of a swing towards the chilly side of stove - land!

I just want to get it right....

One question though, to help ease my mind.... How much of a gap should I leave between the logs and the baffle? And how much and how long over 600 deg (stove top) would constitute an overfire on a Jotul f3 CB...

Aye... I know... That was two questions....