Jotul Oslo--overnight burn and coal build up

If you have large amounts of coals building up during the day, but on overnights the coals burn all down to ash then this sounds fairly typical. However, the buildup of coals during the day could be the result of a few things. 1) Your reloading frequently to keep max heat output and never really giving the coals a chance to burn down or 2)your wood has a somewhat higher moisture content which is causing them to burn down much slower.

Your average stove is going to have active flames from 2-4 hours, and then a coaling stage for 3-6 hours, or longer in both cases depending on the stove and type. The coaling stage is a normal stage for any stove, and is where alot of the heat in a burn cycle comes from. When you look at a burn cycle from the big picture you have a couple hours of good flames where you get max btus/hr, and then as the burn cycle progress into and through the coaling stage your btus/hr will decrease. You may start with say 50k btu/hr output, and at the end it will be 12k btu/hr.

Do you have large chunks of unburnt charcoal/wood/coals in the mornings after an overnight burn, or anytime? If so this may point towards a wood moisture issue. Have you checked your wood with a moisture meter?

What he said. Absolutely.

The Oslo, and other stoves of its kind operate on a cycle: fresh load, high output, coaling, back to fresh load again. If you attempt to return to high output during the coaling part of the cycle by putting in a fresh split or two you will end up with a stove full of coals. Or If the wood is not dry enough it never gets hot enough to burn off the gases and it all just settles into a partly burned pile of coals.

I burn oak and hickory (because that is what my woods are full of) so your experience may be different with different wood, but I load my stove full, get the stove top up to 450 deg. or so, allow it to burn down to coals that would approximate the volume of one largish split, rake the coals to the back, and reload. The stove top temperatures will rise to 450 - 500 deg. and down to about 300 deg. during that cycle. This will take three and a half to five hours.

To hold the fire overnight I place one round or a largish split on the bottom at the back. If I load at around 11:00 pm I have some nice coals and maybe about a fourth of that round for re-starting at 6::30.

And I had a stove back in the 80's and there is no way I'd trade. But I will grant that those old stoves were not near as particular about moisture content.

ButtonwoodHollowFarm said:

Our overnight burn process seems a little inefficient, but perhaps we are expecting too much. We get the fire going really well, adding to it until we can sustain a fully loaded set of big pieces.

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I'd like to understand your burning practices a little more. I don't think you want to be adding to a fire that is going really well. The idea is you load it up over a bed of hot coals, everything gets going at once, and you slowly close it down. If your wood is less then ideal, you can help it by mixing some dryer and smaller stuff in with larger and wetter stuff.

ButtonwoodHollowFarm said:

Jotul8e2, when you say rake the coals to the back I'm wondering why. My thinking was to rake them flat or towards the front where the air enters? Can you explain?

Thanks!

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It is simply easier to rake them to the back than it is to rake them forward without raking into the glass and possibly striking the glass with my ash shovel (I have a 60 year reputation for clumsiness to maintain). I have tried both ways and over all it seems to make little difference.

The one exception is my final load for an overnight burn. Then I rake to the middle as I want a round or large split against the back, and pile the rest of the load up and over the coals. And for the overnight burn I do not open up the air for the fresh load - I just leave it open to the 1/4 mark, or a bit less and let it take off on its own. On several occasions I have been back up an hour or so later and it is burning well, with good secondaries with no attention from me at all. This can only be done with truly dry wood, however.

For me the Oslo doesn't need the coals raked around a lot. Since the stove is wider than deep, the coals burn evenly. Sometimes I break up the coals, before reloading. It all depends what heat you need. More heat required reload sooner. I normally reload with a few inches of coals on the floor. I like a bed of coals. It makes the reload light up easy. If I don't need a lot of heat, I find it better to let it burn out, rather than trying to burn the stove at low temperatures.

But if you don't have dry wood, it gets a lot harder. You will need a hotter stove to keep it burning. If the wood is new to you, more than likely it is not seasoned.

I too read to rake to the front but have started to rake to the back. I also cut two pieces of angle iron and set them in north/south. Creates airspace underneath when I put splits on top. This airspace was something I didn't realize was important. I was just jamming it full as I could. I take my coals to the back and pile up against back wall. Load splits in front of coal pile. Toss in two kindling sticks on top of the coal pile. The splits loaded on front keep the from rolling off. Close door to just a crack open and woosh! I have had much more consistent fires. Higher temps. Last nights fire was great. Loaded at 9:30 got'r up to 450 and shut'r down by 10. This morning at 6am I raked the coals back and there were little blue flame popping up! As easy as it gets in the morning!

ButtonwoodHollowFarm said:

Hi! I'm new to this forum and would just like to say sorry if my questions have already been covered! Welcome to the forum


Looking for advice in two areas with our Jotul Oslo stove.

1. During the day when we are burning we often get a huge heap of coals building up--like the wood is not burning down all the way? We rake the coals and open the air so they burn down before trying to reload it. Just wondering why we are having the coals building up so much. As mentioned . . . either the wood is still not seasoned . . . or you are reloading too often. My guess . . . reloading too often. Many folks equate heat from a woodstove with the flames and don't realize that you get just as much heat from the coals. Generally, unless I really need to reload earlier due to extreme cold, I don't reload until the coals are the size of baseballs . . . or softballs. This helps prevent an excessive build up of coals.

To help burn down a large pile of coals I put a single split on the pile of coals (often softwood) and open up the air . . . within a half hour or so the coals have decreased.

2. Our overnight burn process seems a little inefficient, but perhaps we are expecting too much. We get the fire going really well, adding to it until we can sustain a fully loaded set of big pieces. We slowly crank down the air intake until its down and then turn in for the night. Often in the morning there is hardly any coals left. Is there a better way to get a good overnight burn? This is a big stove, but seems less efficient overnight than our 1970s Upland! Is it a wood quality or type problem? Should we perhaps burn our best and biggest hardwoods thru the night? Would that give a longer burn? Sounds pretty normal . . . well mostly . . . I don't keep adding to the fire. I just reload it when it reaches the small coaling stage and then when the temps are up on the stove and stove pipe start decreasing the air to the point where the secondaries are burning and the fire is not going out. In the morning -- usually 5-7 hours later there are enough coals to easily start up the fire again . . . although heat output is at the point where the stove isn't really heating up the house a whole lot. Overnight loads tend to be the better BTU wood and I tend to pack it in a bit tighter with some sizeable rounds or splits -- I actually split up large rectangles and square splits just for this purpose.

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When reloading if there are only a few coals I tend to rake the coals towards the front with the incoming air to help get the fire going. If there are lots of coals I just rake the coals to spread them around evenly.