Block Arch Efficiency

[Matt H]

We have about 30 taps out and am looking to increase our new cinder block arch's boil rate beyond the current 5.5gph. Is this a fairly normal rate?
I'm hoping to get it more efficient on a LOW BUDGET....a single income family with 4 little ones requires a tight ship! LOL

I'm looking for help finding the most cost effective options for under $50. Here are some spec's:
*3 course cinder block arch
*4 full size, 6" deep steam pans held by an angle iron frame
*19" wide X 24" deep fire box lined with paver sidewalk bricks
*1-2" between bottoms of 2 rearward steam pans and bottom of flue also lined with paver sidewalk bricks
*steel, non-insulated cover for door - air is able to seep around sides
*raised fire grate (3" high I believe)
*6" diameter, 8' tall stove pipe with damper (only run with at wide open)

Ceramic Insulation for the "door", pan frame, etc. looks like it should be my next step, but is too pricey.

Ideas are much appreciated!
Matt

[barnbc76]

One of the problems I ran into with my block arch was not having enough room under the grate, 3" may not be enough because it often fills up with coals and airflow is affected. A blower will help A lot burning the coals all the way into ash.

[ecolbeck]

Back when I had a block arch I got a cheap bathroom exhaust fan and some round metal ducting and blew air in under the fire. It melted the grate that I had but I got 9 gph out of a 2x3 pan.
Make sure your wood is split really small and add small amounts of wood every 5 min to keep it ripping!

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[maple flats]

What is the actual surface area of the pans total? If you get somewhere near 1.5 gal/sq ft of surface for your evaporation, you are good, if much below that look for ways to improve it.
Fire needs 3 things, fuel, heat and oxygen. If the fuel is dry and split fine, figure how to get more air to it. Air just seeping thru the cracks is likely too little. The next thing, you might be choking the fire with a 6" stack, either add 2' height or go to 7" or 8". You do not want a damper, for now try to wire it at the knob to prevent it from even slightly closing. Once the fire is lit heat is not an issue, regulate the air and fuel.

[Big_Eddy]

You're not likely to get much better. Smaller wood, more frequent firings, blower. Keep it ripping.
Best thing you could do would be to lengthen the block arch and add some extra pans at the end. Extra length = extra evaporation for the same amount of effort and wood.

You haven't mentioned sap depth. If you dare - run 1" deep. You'll need to watch for scorching on the sides and you will need to add sap often - but shallow pans evaporate sap significantly faster.

[Matt H]

Thanks for the input!

Talk about a shot to a man's ego...my wife ran the rig today and got 7.5gph instead of my measly 5.5gph! LOL She used some drier wood and kept the first 3 pans right around 1" deep. The 4th pan was used for preheating. What a great wife!

Unfortunately the 6" pipe is all we have on hand. I did notice that the stove pipe is not all that hot. Also pots sitting on steel surrounding the stove pipe aren't getting even warm. This seems odd to me.

No electric power near the block arch for a blower. So hopefully a change to the grate height will do the trick. Is 6" about right?

Each pan is roughly 12" X 20" for a 4 pan total of 6.7 square feet. We've got a way to go to reach the optimum 1.5 gallons/square feet.

[Matt H]

You're not likely to get much better. Smaller wood, more frequent firings, blower. Keep it ripping.
Best thing you could do would be to lengthen the block arch and add some extra pans at the end. Extra length = extra evaporation for the same amount of effort and wood.

You haven't mentioned sap depth. If you dare - run 1" deep. You'll need to watch for scorching on the sides and you will need to add sap often - but shallow pans evaporate sap significantly faster.

Thanks that made a 2gph difference between proper wood and sap depth....was 5.5 now 7.5!

[Matt H]

What is the actual surface area of the pans total? If you get somewhere near 1.5 gal/sq ft of surface for your evaporation, you are good, if much below that look for ways to improve it.
Fire needs 3 things, fuel, heat and oxygen. If the fuel is dry and split fine, figure how to get more air to it. Air just seeping thru the cracks is likely too little. The next thing, you might be choking the fire with a 6" stack, either add 2' height or go to 7" or 8". You do not want a damper, for now try to wire it at the knob to prevent it from even slightly closing. Once the fire is lit heat is not an issue, regulate the air and fuel.

As I reflect on the lack of heat in the stove pipe, I believe the arch might be losing too much heat to create a good draft. Initially the first boil went well and stove pipe was noticeably hotter. Last night was the 3rd boil and I could almost leave my hand on the pipe! Overall, I'm guessing the problem is a stack up of issues??? Some we fixed on the 3rd boil last night (using smaller, drier wood and keeping the sap level lower increased 5.5gph to 7.5gph) and some issues still need to be resolved (raise fire grate this year, stove pipe size and add blower next year). As each boil continues, I also see where the pans are warping and creating gaps between each other...some gaps are now 3/8".

I'm thinking this should be my strategy for this year...
1. Raise the fire grate and/or modify door - Is there an ideal height/setup for the fire grate and door combo? Maybe some dimensions or guidelines to follow? This should be fairly easy, as I have scrap steel, metal fab experience, and equipment.
2. Find heat loss and fix - Your 1.5gph/sqft guideline coupled with lack of heat in the stove pipe indicate to me there is a major heat loss somewhere in the system. Do you think the pans' gaps and a lack of insulation would cause that much heat loss?

[barnbc76]

A taller stack can create more draw, maybe add another 4'. Try to use very dry wood, last week I used a bunch of real old 2x4's they were so dry they burned real fast, taking us from our normal 8gph to 10gph.

[Matt H]

A taller stack can create more draw, maybe add another 4'. Try to use very dry wood, last week I used a bunch of real old 2x4's they were so dry they burned real fast, taking us from our normal 8gph to 10gph.

Wow, that's amazing! I never knew how much that would affect the boil rate. Ironically, we just got done splitting some nice dry ash into wrist size pieces for the next boil too.
I'll see what I can come up with to extend that stack height. Another thing to note is this used pipe we found and are using, not only had a damper but also a rain cap. Maybe the rain cap and damper both are choking off the draft???