burning sap

[Gazing in Wonder]

I bought some douglas fir and much of it is heavy with sap. Many pieces have thick layers of goopy yellow sap, and I'm worried about this leading to creosote buildup in my chimney and/or stove (Morso 5660 insert). It was supposed to be "clean and dry premium" firewood, but it's kind of a mess. It's been about 5 or 6 years since I've been able to find good firewood to buy, at any price.

 

[stoveliker]

I've burned a good amount of (not Doug but) fir with similar sap n what I think were windshake defects, (as well as pitch pine, which is worse....)
Not a problem if it's dry - and if you stack it now off the ground and top covered it'll likely be okay this coming winter.

You do have to be able to control the draft so it doesn't suck smoke past the reburn tubes too fast.

@Highbeam may be even burning more of the stuff.

 

[Slimdusty]

That sap will burn hot, try mixing the sap wood with other non sap wood in the stove. That, along with it being dry and a reasonable air setting to allow a clean burn shouldn’t allow much for creosote buildup.

 

[Slimdusty]

Take some of the sappy pieces and split real small, excellent kindling/ fire starters! Saw a small pack of that in the big box store today for $8.

 

[Highbeam]

I do have experience with this problem. The pitch is an accelerant, might as well be diesel fuel. It will heat up and boil/bloom in your firebox and release all of that fuel in a short time. After that bloom burns off the wood itself will burn like usual. With the fir, the pitch is usually in a layer and not throughout the wood. That's why it is so visible. You could cut it off but that's a lot of work.

So during the bloom in this very fuel rich environment you can provide sufficient air which will combust most of this fuel bloom into immense heat or you can try and restrict air which will keep the firebox cooler but puke that raw fuel into your chimney leading to black smoke emissions and sooted chimney and firebox. If the flue temps are high, you are not likely to get gooey creosote accumulations but soot and stink. Even if you provide large amounts of air, which your noncat stove will do by design, you still will have a hard time combusting the fuel bloom, there's just so much. Since your noncat will dump air into the firebox you run the risk of a runaway stove getting too hot because more heat creates more draft which sucks in more oxygen which makes more heat, round and round until things run away.

I recommend not burning the fuel in that picture without diluting it with non pitchy wood. A chunk at a time might even be too much. Start very slowly. Pitch side into the ash.

I thought it would be fun to burn that pitch wood. More BTU! It was not. The pitch melts and boils and runs off and can splatter onto the glass. Even cat stoves have a hard time eating all of the fuel bloom. All of these stoves are designed to burn wood safely and cleanly, that thick layer of fatty pitch is not wood. When it was fresh cut green that layer of pitch was like crisco and gooey.

What I have found to be best way to get good fuel in our area is to purchase it ahead of time and dry it yourself at home. Even green fir if stacked now is usually ready to burn by fall. I personally buy log loads and process right about now to be stored until the following burn season so about 1.5 years.

 

[begreen]

I burn doug fir a lot, almost exclusively most years for over a decade. At this point I know the stove, draft variances, and loading procedures that I don't separate out any except the very sappiest pieces. Those extra sappy ones usually will be the top center log in a top-down started fire. The others, I just burn. Mixing in with big thick splits helps. They are packed tightly, N/S, with the boost air is blocked on our stove. If the draft is extra strong on a very cold day, I may need to close the flue damper to stay ahead of the bloom, but often this isn't needed with our normal 35-45º winter draft - on our stove. This is where a digital probe thermometer really helps.

Ok, that said, you have a different non-cat entirely with a smaller firebox. My guess is that you need to load it E/W, maybe 3-4 splits at a time. Is that correct? How tall is the flue liner on the insert? If draft is extra strong due to a very tall liner, then paying close attention to turning down the air, as quickly as possible without smoldering the flames, may be necessary. If it is possible to add a flue probe thermometer, that really helps with knowing when and how much to turn down the air.

 

[Highbeam]

Even burning that wood out in the campfire will make stinky and often black smoke. It's not that much different than burning plastic.

 

[stoveliker]

think it depends a lot on the draft situation. Not only runaway (bloom) issues but also the capacity of the secondary (clean up) burn system to handle what is being thrown at it.
In my case I have had boxes full of fir splits with the 1/8" layer of butter on them that did not result in smoke after 10-15 minutes (after a hot reload). I.e. initially there is smoke, but (after a quick dialing down) it settled in front r a longer clean burn.
(And my pitch pine bubbles out a lot more sap than the covered fir as it's distributed throughout the split rather than in layers like the first - though this possibly conveniently allows for more controlled release of the pitch)

I do have a long horizontal run limiting my draft though, and it's a basement stove. So maybe less draft is useful for this wood. (Though I don't have smoke roll out issues upon hot reloading.)

So particulars of the install and user actions matter a lot, as the above posts already indicate.
It can work. And if not, East/west, big splits, mixing will all help as suggested above.

 

[begreen]

Yes, top-down starting also helps a lot with reducing the bloom.

One thing not mentioned. Handle carefully and wear gloves. Sap can be really sticky and a PITA to remove from clothing and hands. This year I will be burning White Fir (Abies concolor, aka Colorado Fir) for the first time. It looks a lot less sappy than Doug Fir.

 

[Gazing in Wonder]

...

Ok, that said, you have a different non-cat entirely with a smaller firebox. My guess is that you need to load it E/W, maybe 3-4 splits at a time. Is that correct? How tall is the flue liner on the insert? If draft is extra strong due to a very tall liner, then paying close attention to turning down the air, as quickly as possible without smoldering the flames, may be necessary. If it is possible to add a flue probe thermometer, that really helps with knowing when and how much to turn down the air.

I do load E/W, 2-3 splits at a time. The flue liner is just one story through a shallow pitch roof, not all that tall. I recently insulated the attic (a long overdue task), and have had to re-learn how to run the stove without overheating the house.

 

[begreen]

Well done! Insulation is good move. It will pay off year-round. Relearning the stove routine is a nice problem to have.

 

[EbS-P]

The only time I saw my stove glow I saved a big split and had it drying by the fire for days and on a real Cold night I did a hot reload with it and boy there was no slowing it down!