AUF/AOF Major problems!

[BRL]

Hey all we have a major issue on our new arch. We had our first boil last night and it was a disaster. How much air should we putting under and over the fire? The firebricks were mortared in and I fireplace cemented the gaps on the fire board and still was leaking smoke everywhere! We only ran the AOF fan for a few minutes but shut it down. Its a 2x6 arch with 14' of 8" stack. So bummed last night, but on a plus side we boiled down about 80 gallons in 3 hours and the first hour didn't fire much so the firebrick could warm up slow. My dad is going to grab a bunch of tubes of fire caulk and go to town on it this morning. Anyone have any ideas? Is there a calculator for how many CFM's we should be dumping in.

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[Woodsrover]

Put the fan on a rheostat and start off slow. You should be able to increase fan speed as the chimney warms up and drafts better. That said, 14' isn't terribly tall. Another length or two of pipe should help your draft as well.

[buckeye gold]

Did you use refractory cement? I would use refractory and completely cover the bricks, trowel it right over them filling gaps plus. It kind of late to do that now though, as you really need to cure refractory. After I was done you could not even see the seams of the bricks. Now after three years some of the refractory is peeling off and I'll need to redo it next year, but it has seen a whole bunch of heat and I have zero smoke leaks. I have ceramic blanket behind the bricks and you can put your hand on the outside of my arch at full fire. So air is not getting out either.

[BRL]

Yes each fan is on one of these
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I did adjust the low speed setting down at the end of burn and I watched the smoke stop leaking out, but it just didn't seem like much air. (We ran it on low all night but it has a little fine tuning screw)

[maple flats]

What do you have for a blower? Where are the AOF nozzles in relation to the bottom of the pan? What size are the nozzles? What angle do they blow into the fire? Did you get the fire lit and the stack warm before turning on the blower? Do both run off the same blower? If yes, do you have a valve to control each independently? What percent were they opened?
On AUF, is that high pressure? How is that air distributed? Is your wood dry?
If all was right on sizes and design, you may have simply been in a downdraft situation.

While I run both off one blower (of unknown output, it is from an old factory and is 100+ years old) I find that it is best to do things in a certain order when lighting the fire. I make sure the stack flip top is open, lay up the fire (I use no kindling, just the wrist size wood I fuel with) then I use a big weed burner torch. I first point the flame over the wood for maybe 15 seconds, then I point the flame at the bottom of the wood and leave it there until it is fully lit. Then I close the doors and turn on the blower. From then until about 45 minutes after my last fueling the blower never gets shut off, not even to fuel. On my air distribution the blower is outside in a wooden partial enclosure under my head tank. It attaches to a 4" PVC pipe. I have 4 long sweep elbows from there leading to under the arch. Under the arch the 4" PVC splits into 2 threes. Each has a 3" ball valve. The AUF valve is open about 25% and it feeds a 4" heavy stove pipe, blowing in the back of the firebox, under the grates. That pipe ends with a cap about 6" from the fill doors. In the pipe I have 3 rows of vent holes, one top center and one row each pointing towards the outer edge of the grates. The holes are 1/4" and are spaced at 3" apart.
For the AOF the valve is open about 2/3 and from there the pipe connects to the manifold for the nozzles thru the ramp. The manifold is not to specs for what the UVM report states. The fitting entering the ramp and the entire manifold are only 2x2 square tube, specs call for 3x3. Then I have the nozzles at 6" spacing, angled to the opposite side of the fire, 6" below the pan and angled down at 15 degrees. The nozzles are 1/4" black iron pipe.
My stack is 19' tall, 12" diameter (3x8 evaporator). Regardless of the weather or wind conditions I have never had a down draft after establishing the draft (by warming the stack) prior to lighting the fire.
If your answers to the questions at the top of this post are "in the ball park", I suspect the stack just needs to be higher. The answer is likely not the tightness of everything on the stove, my rig is not air tight, I can see the fire between the 2 fill doors (maybe 1/8-1/4" space) and my arch has a rear cleanout door, that is no tighter than the front. My wood is dry and the only smoke I ever get is during the first few minutes after the initial lighting until the fire is going real good. Then as I add wood every 9 minutes, with the blower running, there is no smoke either. All that can be seen out the stack is the heat distorted air flow. Before you buy more SS stack, just add 2' at a time in 24 ga. galvanized stack and try it. You may need 2', maybe even 4' more. That mainly depends on the air currents around your sugarhouse, rooves, trees, hills etc. all affect it.
Once you determine how much more stack you need, this season the ones you added can remain, but then before next year, get SS if you can, if not, just make sure of it's integrity before each season. If using galv. stack all of the time, I urge you to get some 20 ga. made at a tin shop. Then between seasons, keep the inside of the stack dry with either a closable cap or even a bucket will work.
Good luck. Once the little bugs are worked out, you will love using AOF/AUF.

[BRL]

What do you have for a blower?I think my fan is a Dayton 1TDT9 so 800 CFM full open Where are the AOF nozzles in relation to the bottom of the pan? 7" below the pans What size are the nozzles? 3/8" ID What angle do they blow into the fire?About 10 Deg Did you get the fire lit and the stack warm before turning on the blower? Turned AUF fan on after about a Min or so Do both run off the same blower? Separate fans/ Separate rheostats If yes, do you have a valve to control each independently? What percent were they opened?
On AUF, is that high pressure? No low pressure squirrel cage blower How is that air distributed? Through the grates 3/8" gap between themIs your wood dry? 1 year old sitting in a covered wood shed
If all was right on sizes and design, you may have simply been in a downdraft situation.

While I run both off one blower (of unknown output, it is from an old factory and is 100+ years old) I find that it is best to do things in a certain order when lighting the fire. I make sure the stack flip top is open, lay up the fire (I use no kindling, just the wrist size wood I fuel with) then I use a big weed burner torch. I first point the flame over the wood for maybe 15 seconds, then I point the flame at the bottom of the wood and leave it there until it is fully lit. Then I close the doors and turn on the blower. From then until about 45 minutes after my last fueling the blower never gets shut off, not even to fuel. On my air distribution the blower is outside in a wooden partial enclosure under my head tank. It attaches to a 4" PVC pipe. I have 4 long sweep elbows from there leading to under the arch. Under the arch the 4" PVC splits into 2 threes. Each has a 3" ball valve. The AUF valve is open about 25% and it feeds a 4" heavy stove pipe, blowing in the back of the firebox, under the grates. That pipe ends with a cap about 6" from the fill doors. In the pipe I have 3 rows of vent holes, one top center and one row each pointing towards the outer edge of the grates. The holes are 1/4" and are spaced at 3" apart.
For the AOF the valve is open about 2/3 and from there the pipe connects to the manifold for the nozzles thru the ramp. The manifold is not to specs for what the UVM report states. The fitting entering the ramp and the entire manifold are only 2x2 square tube, specs call for 3x3. Then I have the nozzles at 6" spacing, angled to the opposite side of the fire, 6" below the pan and angled down at 15 degrees. The nozzles are 1/4" black iron pipe.
My stack is 19' tall, 12" diameter (3x8 evaporator). Regardless of the weather or wind conditions I have never had a down draft after establishing the draft (by warming the stack) prior to lighting the fire.
If your answers to the questions at the top of this post are "in the ball park", I suspect the stack just needs to be higher. The answer is likely not the tightness of everything on the stove, my rig is not air tight, I can see the fire between the 2 fill doors (maybe 1/8-1/4" space) and my arch has a rear cleanout door, that is no tighter than the front. My wood is dry and the only smoke I ever get is during the first few minutes after the initial lighting until the fire is going real good. Then as I add wood every 9 minutes, with the blower running, there is no smoke either. All that can be seen out the stack is the heat distorted air flow. Before you buy more SS stack, just add 2' at a time in 24 ga. galvanized stack and try it. You may need 2', maybe even 4' more. That mainly depends on the air currents around your sugarhouse, rooves, trees, hills etc. all affect it.
Once you determine how much more stack you need, this season the ones you added can remain, but then before next year, get SS if you can, if not, just make sure of it's integrity before each season. If using galv. stack all of the time, I urge you to get some 20 ga. made at a tin shop. Then between seasons, keep the inside of the stack dry with either a closable cap or even a bucket will work.
Good luck. Once the little bugs are worked out, you will love using AOF/AUF.

My dad is going to grab a section of duct so we can add that to the top, good idea!

Thanks!

[Haynes Forest Products]

I'm with idea you don't need it to be completely air tight. Its a balance between the right amount of forced air and a draft from the right amount of stack.
Remember when it comes to furnace cement if its premixed it Dries and if you mix it it hardens. once a arch is up to heat and pressurized/running the cracks in the bricks have no effect unless they lead to the outside. From the looks of your rig its new and well built.

[BRL]

I hope this is an easy fix! My dads at the shack right now adding 5' of stack to the chimney and fire caulking anything that looks like a crack. I will also crank my fans way back (I'm now thinking my fans are way over sized) I'm going to also try and get my temp probes wired in so we can see whats happening.

[nymapleguy607]

Just throwing this out, What was the weather like when you were boiling? What I have noticed with my arch is that when the atmospheric pressure is low outside I have more of a problem with smoke from the evaporator. What I have done is, on the plenum for my blowers I have added a section of 1" pipe from the plenum to the base of the stack. There is a ball valve that allows me to control how much air I bypass the rest of the evaporator. Basically it acts as a pressure blow off point and pushes the extra air up the stack giving me a little better draft.

[maple flats]

That blower is a squirrel cage, in the specs it shows as only going up to 1" SP max, you need 3". A high pressure blower has paddles that spin, the one you have just flings the air. It will not have enough pressure to mix the air with the hot gasses to give you more complete combustion. Did you read this www.uvm.edu/~pmrc/Combustion.pdf ?. For your size evaporator the blower should be like this or equal https://www.grainger.com/search?searchQuery=1%2F2+HP+high+pressure+blower+f an&ts_optout=true That blower runs about twice what you got, and the CFM at 3" is not even rated, 1"SP and 2"SP are. That is the least blower that will do the job. If you look at the picture of that blower, you can see what the impeller looks like, the squirrel cage type is low pressure, high volume. you need high pressure but do not need much volume. The CFM on the referenced blower will likely be somewhere around 100 cfm if that, it's the pressure that does the work.
Sorry to be the bearer of bad tidings, but I have to answer to the best of my knowledge.
You may at this point, if you don't have the where with all to change that blower, then just use the AUF blower and then plan to correct it for 2019.

[nymapleguy607]

If you can't get a new AOF blower what could work in the short term is an electric leaf blower, That's what I originally used to test out my AOF system before I bought my blower

[BRL]

Sorry to confuse everyone here is what I have

Air Under Fire Fan = Dayton 1TDT9 Blower with speed switch
Air Over Fire Fan = Dayton 7AT93 High pressure blower with speed switch

[Sugarmaker]

I will ask a dumb question. Do you have any cap on your stack? Sounds like you have plenty of air and have ways to reduce it with reostats too. Hummmm?
I had missed your post on the Dayton blower types. I was too lazy to look up the cfm. But as just a guess I would as a 100 cfm blower on each would be about right then dial them in with the variable speeds.
The numbers I have heard for air volumes are 20% for the AUF and 80% for the AOF.
Regards,
Chris

[maple flats]

Ok, that is a good blower. Now for some ideas to get it to work properly.
1. add more stack 2' at a time.
2. wait longer when first firing the rig before turning the HP blower on, have a fully involved fire.
3. add the flat piece of tin or such to block air from passing around the front of the coal bed rather than thru the fire.
4. experiment on the rheostat setting for best blower speed, on both the AUF and the AOF. Once you find the best speed, just leave it there.

When you get them dialed in, you will boil faster, use less wood, have a harder boil under the entire evaporator, run a lower stack temperature (because you are putting the heat into the boil and not sending it up the stack) , you will have no smoke escaping in the sugarhouse and there will be no visible smoke out the stack.
You may however find it necessary to aim the nozzles down a little more. Try without, that angle may work fine. I would however put refractory on to insulate the manifold, the nipples will keep cool enough with just the HP air blowing thru them.

[mol1jb]

You will probably get some smoke leakage till everything has heated up. That is how my rig is for the first 20 min. My stack isnt super high either but after I get up to temp no more smoke.

[BRL]

Success! Got the fans turned way down and she’s humming away at 40GPH and we drew off 1 1/2 gallons! It’s been a good night! Thanks for all the suggestions!

[Haynes Forest Products]

So what was it that made the rig behave and get to work.

[CharlieVT]

Success! Got the fans turned way down and she’s humming away at 40GPH and we drew off 1 1/2 gallons! It’s been a good night! Thanks for all the suggestions!

Congrats! sounds great, you're gonna love it.

I've been running my 4x10 oil fired converted to wood AOF/AUF for a few years now.
It is easy to have the blowers set too high, especially before the fire gets really hot and the draft gets cranking up the flue.

I actually installed a draft gauge as suggested in: http://www.uvm.edu/~pmrc/Combustion.pdf
I don't have barometric dampers, but I still think about doing it, especially those days when the atmospheric pressure changes alot.

It is nice to "set and forget" the blowers, but for efficiency an occasional adjustment is helpful; especially if you don't have a barometric damper.
A stack thermomter, draft gauge, and watch the stack effluent are good indicators.
Also, some will like to turn off or reduce blowers when firing; it is a littler cooler standing in front of the open door and fewer sparks/smoke find their way out the door. I am in the habit of looking at the draft gauge and making small adjustments to the blowers.

Without a draft gauge, if you wait a few minutes after firing for things to settle down in the firebox, check the stack temp and effluent. You can have a target stack temp (too high and you are wasting heat blowing it up the stack, too low and your boil rate falls off). A stack thermeter with a probe, not a surface magnet thermometer. The manual Boiling 101 says: "A forced draft arch should operate with a stack temperature in the range of 800-1000 degrees."

If the stack effluent is still smokey several minutes after firing, reduce blowers a little.
I find that if I have sparks coming out of the stack I correct by reducing AUF and increasing AOF to maintain the same indication on the draft gauge.

HTH

[BRL]

Haynes the big issue were the fans were overpowering, dialed them way back and all is good in the hood! Love only having to fire every 15-20 mins!

[BRL]

Charlie I have a fire box thermocouple and a stack thermocouple that I’m going to get wired up today so we can fine tune the beast! Then get the belimo hooked up for auto draw!

[maple flats]

For 1 day, try firing every 9 or10 minutes, you might be pleasantly surprised. When I was doing every 15 minutes I boiled 68 GPH average, when I went to 9 minutes I got 76 gph average. Use a timer.

[CharlieVT]

For 1 day, try firing every 9 or10 minutes, you might be pleasantly surprised. When I was doing every 15 minutes I boiled 68 GPH average, when I went to 9 minutes I got 76 gph average. Use a timer.

Thanks for this post Dave, I had read of folks who said they were firing every 20 mins with their AOF/AUF rigs. I couldn't make it work with my homebrew rig.
10 minutes on a timer works a lot better. The fire box is open for less time, fewer sticks of wood tossed in... more consistent heat.
Yeah, firing more often, but quick and easy.