Coalgun- Puff backs & Explosions

Good day. My buddy with the AHS130 is in his 4th year. This year he has had more puff backs than ever. The obvious reason is a change of coal. He is still using Kimmel Pea size, but it is a different truckload this year. Obviously it has different characteristics. The first 3 years he would have a subtle boom on rare occasion. This year he has been troubled with heftier puff backs on a regular basis. I'm writing now as he has finally made changes that have made a huge difference. Hopefully a total and forever difference.

Big change #1: He installed a draft inducer with a rheostat. He now has "dial a draft". He wired it so it only runs while the fan is running and maintains a draft of .04. That made a good change, but still he had some minor puff backs.

Big change #2: He finally figured out how to set the Fugi control. The factory found the manual & emailed it to me. Come to find out the control was locked. Attached is the Fugi user manual. On page 19 you'll find the Lock system. Even following the manual it's tricky to un lock it, but we finally got it and then changed the ash temps. Before the asher came on at 130 and shut off at 140. Now it comes on at 125 and shuts off at 130. If any of you have the Fugi control and have trouble let me know & I'll be glad to try & help. Basically he set it at a low of 120, a high of 150, a Hysteresis of 5 and then told it to shut off at 130. It's odd how the "150" remains in the equation, but that's how it likes it. The very last hing you do is tell it the temp you want it to shut off at. His asher is allowed to run whenever it wants. I understand some people have wired it so the asher only runs while the fan is running. If he ever has another boom, this will be changed.

Change #3. He added a thick paper-clip to the bottom of the flapper door.

At this point he has been boom free for four days. Hopefully his issues are a thing of the past & hopefully this info can help others.

You fellows running the Fuji Controllers may find this helpful, it outlines the steps for programming, although it is for a Kiln Oven application, the steps for programming should still apply.

Let us all know if this is of any help.



@ Freddy, What was the outlined steps for unlocking the Fuji, could you write it up in similar format as like I added? What year model S130 is you friends? Wondering what years the Fuji was standard. And when the Dwyer/Love Controller replaced it?

I should think your friend will see great improvements. Lowering the ashing temps will move the fire (hot coals) higher, which is better for when fresh coal is dump in on top. When it is a lower fire, it has so much more fresh coal that produce so much more gases that need to be burned or else!
A proper draft goes a long ways towards keeping gases burned off too.

My belief is, if one has "puffbacks" they must get the fire(hot coals) raised higher in their firepot.

What the digital display reads on the controller may not match the owners manual or even what other AHS owners settings are...keep adjusting lower to get the fire higher and the problem will be gone.

Here is a picture of where I have my Paper Binder Clip:
Notice blue gases are ignited before being drafted away. This photo was taken immediately after blower had shut off.

McGiever wrote:could you write it up in similar format as like I added? What year model S130 is you friends? Wondering what years the Fuji was standard.

No need to try & rewrite it, page 19 of that PDF is a show & tell of how the lock works. Charlie's (My buddy) AHS 130 was purchased new in the Fall of 2008. If I remember, the factory said the Fugi was used for about 2 years.

For sure the changes we made brought the fire higher in the burn chamber. It used to be it was rare to see orange when looking in the view port. Now it's orange most all the time.

Based on my own experience I think Big change #2 is the reason for the improvement--assuming that the unit was always operated with the adjustable hole in the flapper open.

In my own case, for the first time in the five years of operating the AHS 130 I have been completely free of puff backs for the entire season. The big change I made this year was reducing the thermo grate setting so that I also now see glowing coals even a significant time after the last fan operation. The other change for this season was a new load of coal (something I get every year) and until I have a couple more seasons with new loads of coal I have to note that a different coal supply might be affecting my results.

My draft drops as low as .02 on warmer days when the unit has not fired for some time and my own experience with puff backs has been that they occur at the end of a firing cycle--when draft tends to be highest--so I am skeptical that the draft inducer is making the difference for your friend.

It would be interesting if your friend was willing to experiment--try turning the draft inducer off and see if it brings the booms back--try removing the paper clip and see if the booms return.

Freddy wrote:Good day. My buddy with the AHS130 is in his 4th year. This year he has had more puff backs than ever. The obvious reason is a change of coal. He is still using Kimmel Pea size, but it is a different truckload this year. Obviously it has different characteristics. The first 3 years he would have a subtle boom on rare occasion. This year he has been troubled with heftier puff backs on a regular basis. I'm writing now as he has finally made changes that have made a huge difference. Hopefully a total and forever difference.

Big change #1: He installed a draft inducer with a rheostat. He now has "dial a draft". He wired it so it only runs while the fan is running and maintains a draft of .04. That made a good change, but still he had some minor puff backs.

Big change #2: He finally figured out how to set the Fugi control. The factory found the manual & emailed it to me. Come to find out the control was locked. Attached is the Fugi user manual. On page 19 you'll find the Lock system. Even following the manual it's tricky to un lock it, but we finally got it and then changed the ash temps. Before the asher came on at 130 and shut off at 140. Now it comes on at 125 and shuts off at 130. If any of you have the Fugi control and have trouble let me know & I'll be glad to try & help. Basically he set it at a low of 120, a high of 150, a Hysteresis of 5 and then told it to shut off at 130. It's odd how the "150" remains in the equation, but that's how it likes it. The very last hing you do is tell it the temp you want it to shut off at. His asher is allowed to run whenever it wants. I understand some people have wired it so the asher only runs while the fan is running. If he ever has another boom, this will be changed.

Change #3. He added a thick paper-clip to the bottom of the flapper door.

At this point he has been boom free for four days. Hopefully his issues are a thing of the past & hopefully this info can help others.

I see a pattern developing here...

pete6500 wrote:Been a while since I've read the posts. I left a post in regard to me keeping my fire as high up as I can so the fire is about 2" below the funnel outlet. I burn buckwheat and my flapper is the old style with no hole. I also have the grate timer which I adjust in relation to outside temp to keep the fire high. during high demand in cold weather I very seldom have to adjust it to keep the fire where I want it. One thing I have to mention, when the blower turns off and the flapper opens, I can hear and see the blue coal gas burning a nice flame. The key here is to see the blue flames. If I don't, the coal gas is not being burned and can travel into the flue by natural draft then get ignited. BOOM!!!! It's been fine this year with no booms as long as I maintain my fire high and nice blue flames. I hope this may help thanks for listening.

Bob wrote:

Yanche wrote:What can we do with what we have?

1. Make the aquastat differential a minimum. This will get the combustion blower burning sooner, hopefully reducing how much the fire get disturbed because the blower cycles on and off more frequently.

2. Lower the ashing rate by lowering the grate motor speed. "rychw" is trying this.

I all this fails then what's left? Changing the concentration of coal gases so that an explosive mix doesn't exist, i.e. a purge of the boiler firebox. A control method is still to be developed.

I would add one element to the above list:

3. Raise the level of the burning coal in the firebox so that the coal gas is always exposed to an ignition source. To put it another way continuously burn off the volatile gases rather than letting them accumulate.

Bob wrote:In my own case, for the first time in the five years of operating the AHS 130 I have been completely free of puff backs for the entire season. The big change I made this year was reducing the thermo grate setting so that I also now see glowing coals even a significant time after the last fan operation. The other change for this season was a new load of coal (something I get every year) and until I have a couple more seasons with new loads of coal I have to note that a different coal supply might be affecting my results.

*********************************************************************************************************************
On a different thought...

rychw wrote: I've noticed the there seems to be a correlation between the frequency of the puffs and the boiler running to reheat after domestic hot water call. That is interesting since the fire would not be as strong when reheating from hot water call as it would be from heat call.

Perhaps, due to some unique features of your particular installation, your best solution may be to add an Indirect DWH tank...this would act as a Buffer for the light load you are experiencing on a DHW call.
Also, having an adjustable differential for the Indirect/Buffer Tank would make it tunable to have a longer run when firing the boiler and get the stronger fire that appears to be necessary.

I realize it shouldn't take all these kinds of measures to try and make this operate properly, but what other courses are there?

*rychw*, How high is your fire?...What setting do you have for ashing?

McGiever wrote:
*rychw*, How high is your fire?...What setting do you have for ashing?

Many pages ago I posted:

It would be interesting to gather members data on their ash thickness, fire thickness and unburnt coal thickness. The only way I could think of making these measurements would to to poke a coat hanger wire in from the inspection port down to the grate. Let it there a while and then pull it out. The cherry red would be the burning coal thickness, below it the ash thickness and above the raw coal. Any thoughts if this kind of data would be useful for comparison purposes?

Did anyone try it?

As you wish. Gave me a reason to use the scrap 10? ground wire.


IMAG0188 by ValterBorges, on Flickr

It got soft after it was red hot, thus why it's all bent, sticking it in a second time was difficult

It was glowing between inches 4" and 8".

SV at 120.
Boiler Temp 150.

0-4" - Ash
4-8" - Burn
8-9" - Coal.

Since it forms an oval shape with the highest point being the exit of the hopper neck it depends on how you measure or insert the stick. Unless you get a really long piece and drive it in thru the hopper.

I have an Axeman Anderson 130M...burning Buckwheat w/ lots of fines.

Anthrastat @135*F (not calibrated)

Idle draft steady @ above .025 inch WC

High Limit set @ 180*F HiHigh Limit @ 210*F, no dump zone.

DHW load w/ Indirect might have been larger than heating load,been in the 50's & 60's.

200*F water & Idling for past hour and most of the last 24 Hrs.

0-4" Ash

4-8" Red Coals

8-12" Raw coal

Yanche wrote:
Many pages ago I posted:

It would be interesting to gather members data on their ash thickness, fire thickness and unburnt coal thickness. The only way I could think of making these measurements would to to poke a coat hanger wire in from the inspection port down to the grate. Let it there a while and then pull it out. The cherry red would be the burning coal thickness, below it the ash thickness and above the raw coal. Any thoughts if this kind of data would be useful for comparison purposes?

Did anyone try it?

I haven't tried the wire. It seems to me that direct observation can be just as effective and doesn't have the problems mentioned by WalterBorges. To make the observation method a bit more scientific pictures could be taken and posted along with the time since last firing and any other variables that may be important.

*rychw*, How high is your fire?...What setting do you have for ashing?[/quote]

I haven't measured the fire but it is approximately 3 " below the funnel when the fan is running. My high temp is 160, my low temp for the fan to come on is 145. My ash grate dump temp is 110 with 5 degrees for my Hysteresis. I've slowed my ash grate motor speed by approximately 1/3 it's usual speed. I have continued to have puff backs that are mostly occuring when there is domestic hot water call.

I am sort of a rookie on some aspects here, but, hope someone more experienced might comment on your High and Low settings.

I'm thinking they would have a significant effect on those DHW calls for heat, but hesitate to advise.

rychw wrote:
I haven't measured the fire but it is approximately 3 " below the funnel when the fan is running. My high temp is 160, my low temp for the fan to come on is 145. My ash grate dump temp is 110 with 5 degrees for my Hysteresis. I've slowed my ash grate motor speed by approximately 1/3 it's usual speed. I have continued to have puff backs that are mostly occuring when there is domestic hot water call.

Have you tried operating with the high temperature limit set at 170 or 180 and using a 10 differential to see if it would help? From your description it seems as if the level of the fire is still a bit low to ensure that the gases are always exposed to a source of ignition and my theory is that the sensed temperature is affected by the boiler water temperature. Also--do you have the hole in the flapper door fully open?

McGiever wrote:I am sort of a rookie on some aspects here, but, hope someone more experienced might comment on your High and Low settings.

I'm thinking they would have a significant effect on those DHW calls for heat, but hesitate to advise.

From what i've read and seen discussed a few times 160-180F is optimal.
From practice however i find running it lower during days 40-50F+ i burn less coal and the house stays at 72F without overheat. If its colder out it just cycles more, so when it gets colder 20F and below ill set it between 160-180F.
This is normally achieved in oil boilers with an outdoor reset.

I also adjust the ashing according to outside temps.

I dont run it less than 145F cause I dont want condensation issues.

This forum has great info and I realize how frustrating these puff backs can be. I too have had my share. I'm on my 4th year and still learning. I know one thing, I have to keep my fire high to see the blue flames or BOOM! I have the timer grate and have to adjust it to the outside temp no matter what I run my water temp at to keep the fire high. I also adjust my water temp when the weather get cold or warm but I always keep the fire about 1" -2" below the funnel outlet. One story I'd like to share. Back in the day just about everybody burned coal including my father. He always said there was an art to burning coal (long ago when you shoveled the coal by hand) and there was a golden rule. The rule was that you never ever shoveled too much coal on to smother the the fire, you shoveled just enough to keep the blue flames burning through the newly added coal.If you did you were asking for trouble.I think it still hold true today. As long as I adjust my grate to see the flames I never have even a "puff". I've thought about upgrading the thermo ash sensor system but as long as I continue doing what I'm doing I honestly don't want to spend the money. On top of that I feel I have better control over the process. I sure hope this helps and again thanks for all the info!

Bob wrote:Have you tried operating with the high temperature limit set at 170 or 180 and using a 10 differential to see if it would help? From your description it seems as if the level of the fire is still a bit low to ensure that the gases are always exposed to a source of ignition and my theory is that the sensed temperature is affected by the boiler water temperature. Also--do you have the hole in the flapper door fully open?

Bob, I have tried to operate at a higher temperature without eliminating puff backs. I hesitate lowering my ash dump temperature below 110 degrees but that may be my next move. I changed the differential to 5 from 10 that it was at for 5 years. The theory is that there will be less new coal added for only 5 degree differential preventing puff backs. The whole in my flapper is open all tha way.