chimney length

[tbear]

So I've been reading in preperation of the 2012 sugar season. I use a cement block arch with a 2x4 flat pan. I stacked the cement block as high as I could safely go ( about 4 ft. 6 in.) for a chimney and called it good. Yesterday I read that the stack should be at least twice as high as the pan is long. Reading further I found a post from "Groves" about shoving a couple 5 in. diameter HVAC pipes into the holes of the top chimney block. Thought to myself "Hey that sounds good!" ran out and purchased a couple 5 ft. lengths. Apparentley what I lack in understanding and knowledge I make up for with enthusiasm (sp?) because I have no idea why a longer chimney is a good thing. I'm sitting here laughing at myself! Could someone please tell me what to expect from this chimney addition? Thanks, Ted

[Jec]

You will get a better draft. That means a hotter fire and the smoke will get sucked out. Starting the fire will also be easier with a higher chimney. It gets better draw.

[adk1]

Jec is correct for sure. Draft is key. the higher the chimney the better the draft.

[tbear]

So...higher chimny = better draw; better draw = hotter fire? I'm speculating here but... Hotter fire = higher boil rate?

[adk1]

sure does which also means, being more careful that you dont burn your pans!

[tbear]

Thanks for the info and the word of caution!

[Peepers]

tbear - make sure those pipes are shoved in the blocks good and tight if that is the only means of support. For safety you might want to add some support wires or something. I used some scrap sheet metal on top of my block arch with a 4' length of 6" HVAC pipe for a few years now and even just 4' of straight pipe was a vast improvement over just blocks. When its stoked up you can hear it roar and at night I have 3-4' of fire coming out the top of the stack. It boils like crazy like this and about half of the stack glows red. I fastened the stack on really good and have a few extra blocks placed around it for added support but I still cordone off the area around the stack to be safe - especially when the wind is blowing good. I don't want a glowing-hot stack falling on anyone!

[maple flats]

The ball of fire out the top is not flame from the fire, it is unburnt gasses getting new air and igniting. A simple block arch likely is not the place to remedy that. In a regular arch that is fixed by adding high pressure air over fire (AOF) There is no easy way to fix that and I'm guessing the block arch will just be a short term stepping stone in an addiction that is very likely to grow like it has for the vast majority of us.

[tbear]

I see this as another perfect opprotunity to prove my ignorance by opening my mouth...but here it goes. If I ran a small table top fan pushing air into my block arch would that help as far as draft/airflow go? Would it improve my evaporation rate even more than the chimney extension alone? Or perhaps it would just blow the ashes around and into my pan making a mess.

[morningstarfarm]

use a block arch at my sons school to burn every year..couple things...after you jam the pipe in the blocks...drive a metal t post into the ground right next to it..and use a big hose clamp to clamp pipe to post...makes it much more sturdy..kep your fire as close to the front as possible... the longer the pipe..the more the heat pulls more air into the front of the arch..and the hotter she gets..