Solutions for Bridging?

[Medman]

OK, just when I think I am getting the EKO 25 figured out, I am now having a problem with bridging in the upper chamber.
All of the recent posts on primary and secondary air have been great - I now have a clean, blue-white flame with better heat output and much longer burn time. Yet this morning I woke to a (relatively) cold house and went outside to discover that the load of wood I put in last night was still mostly there, bridged about 8 inches above the nozzle.
My question, for those of you in your second or greater heating seasons with these boilers, is what methods have you found to reduce or eliminate bridging?
My thought is that smaller splits would be better, but woudn't they also burn faster, requiring more loading? Small splits also require a lot more labour in the splitting too - a big factor when I am splitting 25 face cords at a time.
Round pieces seem to work well, but I only have so many, and they are not the best wood.

Suggestions?

 

[Nofossil]

OK, just when I think I am getting the EKO 25 figured out, I am now having a problem with bridging in the upper chamber.
All of the recent posts on primary and secondary air have been great - I now have a clean, blue-white flame with better heat output and much longer burn time. Yet this morning I woke to a (relatively) cold house and went outside to discover that the load of wood I put in last night was still mostly there, bridged about 8 inches above the nozzle.
My question, for those of you in your second or greater heating seasons with these boilers, is what methods have you found to reduce or eliminate bridging?
My thought is that smaller splits would be better, but woudn't they also burn faster, requiring more loading? Small splits also require a lot more labour in the splitting too - a big factor when I am splitting 25 face cords at a time.
Round pieces seem to work well, but I only have so many, and they are not the best wood.

Suggestions?

Going into my fourth season and have never seen bridging. I'm wondering what I'm doing differently. Part of it may be that I have the older design with the flat primary floor. Seems like there have been some issues with the steel guard that they put in to protect the outer edges of the refractory.

I also tend to load it so that I build up the outer sides first, then fill in the center. Each layer that I put in (after the first) is kind of a 'U' shape. That may help it collapse as it burns.

The other difference is almost certainly that I burn smaller rounds and splits. Part of that is because a lot of my wood is buckthorn, which rarely grows to more than about 2" diameter. Part of that is because I have storage and realized that larger wood does not produce more heat. I don't mind a short hot fire.

I've closed down the shutter on my fan to reduce the total airflow a bit so that my EKO typically provides an average of about 55,000 BTU per hour over the course of a fire. It takes five or six splits / rounds to span the width of the firebox. That seems to be enough so that bridging just doesn't happen.

 

[jebatty]

Ditto on smaller splits -- great reduction to elimination of bridging issues.

 

[Medman]

Thanks for the input. The smaller split size is what I thought most effective. Unfortunately for me that means splitting my wood a lot smaller - I am in the 5" range now, as that was the ideal size to achieve long burns in the PE stove. Since most of the wood I get is sugar maple or red oak in the 10" up to 28" diameter range, it means a lot of handling on the splitter or a lot of swinging the maul to get it down to size. Most of the logs here are rejects from the mill harvest, so they are twisted, gnarly and difficult to split even with the hydraulic splitter. By the time I am done, I have popeye forearms.

 

[bird hunter]

I too have had issues with bridging, the first remedy I found was on this forum and that was to reduce fan speed. I am currently at 60% however this may need to increase in colder -0 temps. The problem seems to be caused by the location of primary air outlets in the upper chamber, I find that the wood burns from front to back. The wood in the front of the boiler burns completely and the wood in the back leaves a large amount of charcoal which contributes to bridging. The lenght of the firewood seems to be a big contributor as does the species. When loading firewood for an overnight burn I now load the shortest pieces 18" and less and keep the fuel pulled to the front as much as possible I first use wood with the poorest coaling qualities (cherry and soft maple, small to medium splits) then a row of large oak and or beech on top. The weight of the larger pieces seems to help push the coals down into the nozzle. I believe that primary air outlets centrally located in the upper chamber would help this problem or at least a surface that is angled toward the nozzle. So far I have been able to achieve 8 to ten hour burns and a warm house, I am not covinced that the 40 will be able to heat this old farmhouse in sub zero temps all night without storage as with so many, storage pending.

 

[taxidermist]

On my 60 I was also getting bridging untill I cut my fan speed to 50 percent and I still have good flame in lower chamber but so far no bridging. I will keep playing with it.

 

[bird hunter]

what kind of wood are you burning? I found 50% too weak in the 40, how long are your burn times?

 

[Medman]

I have reduced the bridging a lot by reducing the fan speed to 60%. So far the temps have been OK even on the coldest nights. I still came home to a cold boiler today due to a bridge, but the house was still warm. I am finding that using smaller splits and rounds works better. I am burning small splits of white birch to start, then red and sugar maple and red oak for the long burns.
I am still thinking about reducing primary air to 7mm, but I haven't had a chance to make the adjustments yet.

 

[bird hunter]

I am wondering does anyone else have the issue with charcoal in the rear of the eko? fuel burning from front to back and building coals in rear? This appears to be my biggest issue with bridging

 

[taxidermist]

what kind of wood are you burning? I found 50% too weak in the 40, how long are your burn times?

Oak and cherry mix still working on the burn times I loaded last night at 9:30 and had a great bed of coals at 5:00 am this morning Loaded it up and the wife started a fire tonight at 9:30 and she added paper and kindling and it took off with out a match. Boiler was at 158 incoming water to house was 150 and tank temp was 160

Rob

 

[sweetheat]

I have no problems with bridging. Reduce the lengths of your splits. I've been burning 16" splits, it never gets hung-up. It will take up to 20" length but 18" works better. I do not know what the EKO fire box looks like, but the Tarm 40 is basically flat with angled sides. When I've used up this short 16" wood I will change to 18" long splits. sweetheat :lol:

 

[Tony H]

I also have had a recent problem with bridging using splits , rounds give no problem. What I found to work is alternating the wood with the bottom layerlaid North to South and the next East to West and seems to work real well now.

 

[Duetech]

I am wondering does anyone else have the issue with charcoal in the rear of the eko? fuel burning from front to back and building coals in rear? This appears to be my biggest issue with bridging

I do get bridging with my "no storage" EKO40 with the beveled bottom but usually with larger splits unless I pile those towards the top of the load and use the smaller splits to build the bottom. Kind of a compromise for the extra work the small splits require. The lower blower pressure really helped eliminate the bridging but I have to keep my blower with only about a 1/2" opening. Anything bigger than that and I can watch my boiler temp drop in colder weather even with blue flame gassification. Also I'm going into my 3rd season and have found low moisture to be very critical in preventing bridging with the new settings where high moisture is a culprit.

As far as front to back burning is concerned it sounds like you have a blocked air flow from your secondaries in the rear or an upturned flow toward the front creating extra turbulence. (Next time you take your blower/cover panel off shine a light in your secondary tubes I found ash piled toward the back in mine) One of the newer European {EKO40} designs that I saw a video of is using an increased number of openings that are offset, single row per side and sized at just 10mm for secondary air in a recessed opening, down ward flow and the blue flame was large, tight and uniform in color. According to the video Orlan is supposed to start re-tooling for the newer models to incorporate the change. I digress...If you have a small piece of fire brick "just lying around" that won't slip through the nozzle try putting a two or three or four inch long piece near the front of your nozzle (not all the way forward and preferably directly over the secondary opening) to see if you can "influence" the back portion to burn hotter. You may have to adjust blower pressure or primary air a little, or both, to offset the potential rise in pressure/velocity of the primary air to keep the "ideal blue flame" in the ball park with your secondary settings. The small piece of fire brick can also help you determine if you have an up flow turbulence (vortex) from your secondary air in the bottom of the nozzle.

 

[bird hunter]

Thanks for the info cave2k, I hadn't thought of the secondaries as a possible culprit,Next time I shut down for cleaning I will investigate.