Talking balance of efficiency vs heat. Are they the same?

[acottrell]

Hello all,

With my wood stove install complete and now a week of burning, I'm still left with a few questions on stove operation and whether the activation of the secondaries are really necessary for heating needs.

First off, yes I have seasoned wood, measuring at 10% MC with a meter I bought. Second, I know the secondaries help with the cleanliness of the burn and the general rule of thumb is to get the damper set so little to no smoke is coming from the chimney. Lastly, for reference all the wood I have is 4" diameter splits or so from my old fireplace with only a handful of larger splits.

So from here after watching multiple youtube videos and reading practically every FAQ thread, I'm still looking to understand the balance between where is the best point to burn for heat and longevity vs the most efficient burn with activating the secondaries. For reference, efficiency as I am referencing it is getting the most energy from the wood itself, so a complete as possible burn, instead of how long the wood will last. With that said, is the point where the secondaries are activating actually putting out the most heat? For me, that has resulted so far in 4 days of continuous burning in using a large amount of wood. When I go to the other side of things and don't worry about having a bit of smoke out of the chimney and keeping the damper closed further to have a slower burn, heat output still seems decent as well.

What am I missing so far about this or doing incorrectly? It is already a goal of mine to make larger splits for my upcoming wood stock that I will be generating in the next couple weekends. For reference, I am running a Buck Model 74 in my ZC box/chase with 24-ish feet of 6" class A and do not have any draft problems.

Thanks for your help/suggestions.

 

[jatoxico]

The secondaries are not going to be roaring gates of hell non-stop. Active secondaries mean there's lots of smoke which is often earlier in the burn. Once things calm down the secondaries may be doing there job but not so noticeable.

As long as the stove top is hot enough to give you what you nedd heat wise and the burn is clean (glass and chimney) you should be good.

10% seems low BTW.

 

[CentralVAWoodHeat]

The secondaries are not going to be roaring gates of hell non-stop. Active secondaries mean there's lots of smoke which is often earlier in the burn. Once things calm down the secondaries may be doing there job but not so noticeable.

As long as the stove top is hot enough to give you what you nedd heat wise and the burn is clean (glass and chimney) you should be good.

10% seems low BTW.

Well put. You may get some active secondary activity for a while but don't expect to be seeing a blowtorch secondary show for hours on end. I like the way Jotul puts it. Damper down until you have lazy flames and keep your stovetop thermometer (provided it is placed correctly) in the correct operating range.

What wood are you burning in NC that has 10% moisture on a fresh split? I'm lucky if I ever get that on several year old tulip poplar in a humid climate like the south east.

 

[acottrell]

Well put. You may get some active secondary activity for a while but don't expect to be seeing a blowtorch secondary show for hours on end. I like the way Jotul puts it. Damper down until you have lazy flames and keep your stovetop thermometer (provided it is placed correctly) in the correct operating range.

What wood are you burning in NC that has 10% moisture on a fresh split? I'm lucky if I ever get that on several year old tulip poplar in a humid climate like the south east.

Checked the wood again after splitting a few and numbers are coming back 14-15%. I guess the one piece I tested earlier I didn't get the probes in deep enough on the wood.

As for temps, with my zero clearance insert where I only get the stove door / front face essentially as the one place that isn't insulated. Should I be slapping a thermometer on that or would that not be accurate at all?

 

[jatoxico]

I have to put mine in the vent but you could pick up an IR too.

 

[CentralVAWoodHeat]

Checked the wood again after splitting a few and numbers are coming back 14-15%. I guess the one piece I tested earlier I didn't get the probes in deep enough on the wood.

As for temps, with my zero clearance insert where I only get the stove door / front face essentially as the one place that isn't insulated. Should I be slapping a thermometer on that or would that not be accurate at all?

Where does the manufacturer recommend you put a thermometer?

 

[acottrell]

Where does the manufacturer recommend you put a thermometer?

In Buck's manual, they do not state where to put one. The only reference to operating temperature is that of how the fan will kick on when it hits a high enough temp and that if you see the piping or connector glowing orange that the stove is too hot (no kidding).

Unfortunately that's it.

 

[Doc C]

People complicate burning a stove with burn tubes. A catalytic stove might be different but with burn tubes the goal I always have is to have zero smoke from the chimney and clean glass.

Most of the time once my fire is established that is with my damper closed about 95% of the way. If it’s pine or fir then I usually close it all the way. Very rarely do I have secondaries. The only time I see them is if I’m trying to get my stove really hot.

 

[griam01]

Well put. You may get some active secondary activity for a while but don't expect to be seeing a blowtorch secondary show for hours on end. I like the way Jotul puts it. Damper down until you have lazy flames and keep your stovetop thermometer (provided it is placed correctly) in the correct operating range.

What wood are you burning in NC that has 10% moisture on a fresh split? I'm lucky if I ever get that on several year old tulip poplar in a humid climate like the south east.

I get a lot of secondaries for 2-3 hours and I am all the way dampered down.

 

[Poindexter]

Sounds to me like @jatoxico is trying to hook you up.

14-15% is freaking awesome. You got dry wood. On my cat stove I run on high for 30 minutes and then how long the rest of the sap lasts depends on how far I turn it down.

I have never operated a tube stove, but I did run an EPA non cat a few years ago. As dry as your fuel is, you are gong to have a visible secondary burn for a relatively short portion of the burn cycle, maybe the first two hours of a burn kind of thing.

In the first say two minutes of a load you will have a metric butt-ton available to ignite the secondaries as you burn off the fine hair like bits on every surface of every split. In the first couple (or three hours) you will be melting sap (sugar) and burning that off too.

Once all your sugar and fine hair like pieces are burnt off, what you got left is cellulose - C6 - H10- O5. The hydrogen and oxygen are going to come out of that first, leaving you several hours later in the burn with just Carbon (charcoal) to burn off. I would not be looking for visible secondaries at the ports on the tubes when you are burning cellulose down to charcoal. Certainly "some" of the carbon will get consumed in this longer middle phase of the burn. At the end of burn, just charcoal, you are just burning off the last of the carbon.

I don't see a problem with visible secondary flames vanishing two to three hours into a burn when your MC is under 16%.

 

[acottrell]

Thanks for all the replies. A lot of good information on secondaries and burning in the stove that I wasn't able to get in many of the sticky threads I have read. I'll just continue to burn how I have been without focusing on secondaries and going for longer burn times and steady heat production. If the secondaries go or not shouldn't be the goal I am coming to find.

 

[kennyp2339]

With any stove, but more importantly with a stove that has re-burn air tubes.. temperature, temperature, temperature is the most important thing. If your running the stove to low, the fire box doesn't heat up enough to allow the secondary burn to kick in so you end up burning dirtier, if you run the stove to high then your sending a lot of potential heat up the flue. Every stove, insert, epa fireplace is different, it all comes down to draft, wood moisture content, elevation / climate.
Typically when breaking in a new stove many members have had luck with (after the paint curing process) burning the stove on a full load and start to dial the air back in increments after the unit reaches 450-500f, this will give a little more control and make it easier to find the cruise mode which is between 500 - 650 deg on most units.
The other key indicator other then fire box temps is the chimney cap, look for heat waves only when the stove is in cruise mode, there should be no smoke. Once you get that figured out it gets pretty easy to run.

 

[jatoxico]

Thanks for all the replies. A lot of good information on secondaries and burning in the stove that I wasn't able to get in many of the sticky threads I have read. I'll just continue to burn how I have been without focusing on secondaries and going for longer burn times and steady heat production. If the secondaries go or not shouldn't be the goal I am coming to find.

If you can resist the urge to chase max burn times early on, which admittedly is tough you'll probably be better off at least in the short term. Run hot and see how things look after a sweep or two will help you in getting your burning habits dialed in.

FYI listed burn times usually include the coaling period where the stove is putting off some heat but w/o any visible flames.