Jotul Oslo...builds too many coals?

I know what you mean and I think it's a common phenomenon. Opening the air all the way seems to burn them down quicker, but if you really need the heat and can't let them burn down while the house cools off, you're kinda stuck. When I do let them burn down, I'm always amazed at how little ash is left.

When I have a big pile of hot coals in my little Waterford stove, that won't burn down and that clog up the firebox, it is because the wood was not dry enough.

Rake them forward towards the door, place a small split of kindling on top and with the air maybe half open burn them down. They will still give off some heat and reduce in size pretty quickly. I also like to use dry softwoods like pine when I need to keep the stove humming. It burns hot and quick with very little coals. Thus, I can reload on a small coal base while the stove and house are still warm. I also rake the coals forward every time I load the stove, even at cold startups. That way the coals are manageable.

An excessive coal base could also be the sign of not so dry wood. What moisture content does yours have?

clr8ter said:

Hmmm, interesting thought. But the wood I'm burning right now is at least 3 years old. Mixed hardwood, fair amount of oak.

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"Looks dry" "Been split for years" Etc.. none of those mean squat. Your wood VERY WELL could be dry.. but there is only one way to tell. Pull an average size split out of the stack, split it and measure the moisture of the fresh split face. The split should not be frozen when tested. I was very surprised when I started playing with a MM.. I had oak splits 4 years old, still above 20%..

Not a typical problem for me providing I run in cycles . . . reload when the coals are the size of baseballs or so.

I do have this issue when it's wicked cold outside and I need to do more frequent reloads . . . at which point I rake the coals around the entire base to level them out, put a split on top (typically a softwood split if I have one) and open up the air control. In about a half hour or so the coals have decreased significantly without a huge drop in the heat output of the stove (and without the flue getting too hot).

We suffered with large coal beds in our epa wood furnace, the first year it was due to wood that wasn't quite seasoned and at the time the furnace was too small for the heating demand. Fast forward 4 or 5 years, we burn seasoned wood and since we've insulated and worked on airsealing our home, coaling is not an issue. We were feeding the furnace too much trying to push heat, in return it was producing a coalbed we couldn't reduce. As our home becomes tighter things become much easier.

67charger had a good recommendation. I tried this method yesterday and worked very well. It is the 11th reply from the bottom of page 2
https://www.hearth.com/talk/threads/napoleon-1900-i-think-im-ready.41345/page-2

The Oslo does not build coals any more or less than any similar stove design. To operate cleanly and efficiently it has to go through three stages: 1) ignition of a fresh load with top plate temperatures rising to 400 -550 deg.; 2) burning of the more volatile gases (this is when you get the visible flames from the secondaries); 3) coaling with top plate temperatures gradually falling to 300 deg. or below. You can speed the coaling stage somewhat by pushing the coals to the front and opening the air intake.

If you try to push the stove by loading fresh splits mid way through the cycle it never has time to burn the coals. It is best not to add fresh wood until your pile of coals is no larger in volume than one large split.

Poorly seasoned wood, wood that is damp from rain or snow, and large quantities of bark will all cause you to have excess coals. I think the problem many people have with non-cat EPA stoves is they fail to get the temperature up after a re-load high enough to burn the gases. In fact, without truly seasoned wood it is nearly impossible. This leads to long, slow burning fires that never really put out enough heat followed by even slower burning coals, and unacceptable amounts of creosote in the flue.

clr8ter said:

Well, when I've tested with the MM, it is pretty inconsistent. When the coals get too unmanageable, I do rake them foreword and give them a little while. I ale tend to flatten out the coal bed when I restoke.

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Leave the coals in the front. The air coming from over the door will help in burning them down.

I've found that the wood in the bottom quarter of the pile does not dry as well as the other further up. When I move it under the porch for burning I only take the upper three quarters and restack the bottom layer for another year of drying time. The top layer may also not be quite as dry when not being top covered. You could also have a mix of species.

clr8ter said:

Admittedly, this is exactly what we do, most of the time. We do, however, aim to get the stove to 550 nearly every time we run it. Most of the time it gets there. We have a very small amount of creosote every year. Our chimney guy says we do real well with that.

So, are you saying get the thing going good, stuff it full, and let it burn down to between 2 and 300, then re load?

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that's how we run ours. I use the top temp AND my flue temps to decide the "when".

clr8ter said:

Admittedly, this is exactly what we do, most of the time. We do, however, aim to get the stove to 550 nearly every time we run it. Most of the time it gets there. We have a very small amount of creosote every year. Our chimney guy says we do real well with that.

So, are you saying get the thing going good, stuff it full, and let it burn down to between 2 and 300, then re load?

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The way you are doing it may keep the flue clean but is not the most efficient way. I do the following in a warm stove with hot coals:
Rake the coals forward, drop 2 shorts splits E-W behind the coals (wearing welding gloves!) creating a level surface, load more splits N-S (the preferred orientation in my insert) on top of the wood/coals until it almost hits the baffle. With the door slightly ajar I wait until the wood has caught fire, then close door. Let the fire establish, then start closing the air about a quarter every 5 min. After 15 to 20 min air is fully closed, secondaries are blasting, stove will climb to 650 to 700 F over the next 30 min. I won't touch the stove for at least 6 hours. The insert with still be putting out heat and have hot coals after 10 hours.

Grisu said:

The way you are doing it may keep the flue clean but is not the most efficient way. I do the following in a warm stove with hot coals:
Rake the coals forward, drop 2 shorts splits E-W behind the coals (wearing welding gloves!) creating a level surface, load more splits N-S (the preferred orientation in my insert) on top of the wood/coals until it almost hit the baffle. With the door slightly ajar I wait until the wood has caught fire, then close door. Let the fire establish, then start closing the air about a quarter every 5 min. After 15 to 20 min air is fully closed, secondaries are blasting, stove will climb to 650 to 700 F over the next 30 min. I won't touch the stove for at least 6 hours. The insert with still be putting out heat and have hot coals after 10 hours.

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Thanks for an informative breakdown. I am still trying to grasp a good burn method on my NC30.

Question: you said you don't touch the stove for 6 hours... what do you do to the fire after that 6 hour point then, between your 6 hour and 10 hour time frame?
Do you adjust the air intake?

I am still trying to break the habit of adding an occasional split throughout the burn to keep the fire going longer. (old smoke dragon habit I guess)

6 hours is about the earliest time I would consider reloading depending how cold it is outside. Nevertheless, I use the same method in the evening before going to bed and usually find in the morning about 10 hours later that I have enough hot coals left and the insert will still be putting out some heat. Whether that is enough depends more on insulation level of the house and outside temps than the stove itself.
Occasionally, I will increase the primary air by a tad 5 to 6 hours into the burn to burn down the coals a bit more quickly and to get the stove temps up before I do the reload.

What is working in my BK Ashford is to rake the coals and charcoal lumps to the front, re-engage the cat and open the air to let in as much air as possible.

I believe/agree most of the volatiles and water have been driven off the charcoal chunks at the back, but that last little bit of the load sure does burn hot when it is close enough to the door to be in the airwash and push heat through the glass.

Grisu said:

The way you are doing it may keep the flue clean but is not the most efficient way. I do the following in a warm stove with hot coals:
Rake the coals forward, drop 2 shorts splits E-W behind the coals (wearing welding gloves!) creating a level surface, load more splits N-S (the preferred orientation in my insert) on top of the wood/coals until it almost hit the baffle. With the door slightly ajar I wait until the wood has caught fire, then close door. Let the fire establish, then start closing the air about a quarter every 5 min. After 15 to 20 min air is fully closed, secondaries are blasting, stove will climb to 650 to 700 F over the next 30 min. I won't touch the stove for at least 6 hours. The insert with still be putting out heat and have hot coals after 10 hours.

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I tried the rake forward/load back e/w, n/s on top method today and I think it has promise. The coals become a defacto log.

May I ask what speed you have the fan on for your insert?
I have it blasting right now on high, because even with the air closed all the way, I have lots of fire caused by the secondaries. It would seem that I'd be wasting some of that if I had the fan on low. I'll put it on low after the initial inferno. It's baking me out of the living room right now, but as I said, I think I'd be wasting the heat if I put it on low.

velvetfoot said:

I tried the rake forward/load back e/w, n/s on top method today and I think it has promise. The coals become a defacto log.

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Thanks. It took me 3 years to figure that one out.
Before that I always had splits laying on the coals and going at an angle into the back. Never liked the way how I was wasting valuable firebox space plus the air blowing through the coals and fanning the wood from below seemed to churn though my wood fast. I certainly saw an increase in burn times doing it the way I described probably due to more wood but also the E-W logs blocking the air flow a bit.

May I ask what speed you have the fan on for your insert?
I have it blasting right now on high, because even with the air closed all the way, I have lots of fire caused by the secondaries. It would seem that I'd be wasting some of that if I had the fan on low. I'll put it on low after the initial inferno. It's baking me out of the living room right now, but as I said, I think I'd be wasting the heat if I put it on low.

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Fan is on low to maybe medium during the peak burn, i. e. turned on after maybe 30 min and turned off 1 to 2 hours later. Other than that I let natural convection and the fireplace bricks retaining the heat do their jobs. (interior fireplace)
I am still not sure how much of an effect the blower has on the efficiency of an insert/stove. Would like to see some owners who have a flue thermometer run their units with and without the blower and report the flue temps. I really want to know whether turning on the blower really leads to a significant reduction in flue temps while turning it off will lead to a rise.

The flue temperature would be a good indicator.

clr8ter said:

Sigh. This is not as easy as I first thought 4 years ago. I have an Oslo, and the firebox is way wider than it is deep. So, to stack logs going both ways would mean having 2 different lengths in stock, yes?

At this point, I will try going through the 3 steps in the cycle. As it is, that's kinda what we of overnight. I stuff around 8 isn, and get up around 5:40. At that point, there is usually coals left to re start, assuming there is an ash bed in there. Most of the problems come on the weekend, when we're around to constantly be putting in a piece or 2.

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Sorry if I gave the wrong impression. If your stove is an E-W loader there is no need to put splits N-S on top of the coal/wood pile in the bottom. Just load them as always on top until you almost reach the baffle. Of course, you may need to live with the fact that an occasional log will touch the glass.

clr8ter said:

Most of the problems come on the weekend, when we're around to constantly be putting in a piece or 2.

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Could that be part of the problem?

Grisu said:

Rake the coals forward, drop 2 shorts splits E-W behind the coals (wearing welding gloves!) creating a level surface, load more splits N-S (the preferred orientation in my insert) on top of the wood/coals until it almost hits the baffle.

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I can't wait to try this.