block arch - chimney size

[sams64]

I need to get my block arch put together this weekend and appreciate oll the good ideas and pictures posted here. I am not sure what size I should go with for a chimney. It appears as thought 8 is a standard, however, I have seen a fair number of comments about using 6". This will be a 3 hotel pan setup if that helps.

Sam

[emo]

I have a similar setup. Used a 4" stack that past 2 years, but switched to a 6" stack for this year. The 6" stack does not seem to heat up as much and it is a little easier to reach a boil and keep it now. I measured how big an opening I had in the back of the arch and cast a block with a piece of 6" black stove pipe in it. I used some 1/2" rebar above and below the stove pipe for extra support. Wound up with a 20x13 block of concrete with stove pipe about in the middle, took about 1 1/2 80lb bags of concrete to make it. I have noticed the block has a crack directly about and below the stove pipe, part of the reason for the rebar.

[valleyman]

I have a 4 pan set up and I use a 6". This year I gave it more air under the pans (went up one row of cap block 4") and it burns great. I can to 7 or 8 but I'm Ok with the 6"

I've included some pics.

[vtjeeper]

I need to get my block arch put together this weekend and appreciate oll the good ideas and pictures posted here. I am not sure what size I should go with for a chimney. It appears as thought 8 is a standard, however, I have seen a fair number of comments about using 6". This will be a 3 hotel pan setup if that helps.

Sam

I am using 8 because that's what I happened to find on craigslist for a very good price. otherwise I would have bought 6". mine is a 2x6 foot pan

[fishweasel]

I used a half cinder block and stuck a six inch adjustable pipe elbow into the hole. I had to crimp one end slightly to get it to fit. After that, I used a small bucket of pre-mixed high temperature mortar to fill the gap between the pipe and the block. This was a cheap solution and easy to do to boot. Everything I needed was available at Home Depot. The only minor downside is that it took four or five days for the mortar to set up solid since I filled it in pretty thick. It helped speed things up when I brought it inside rather than leaving it in the cold garage.

[Groves]

We just jammed two 6ft sections of 5" hvac pipe into the holes of our 3 block stack. Worked a treat on our 8 pan arch.

http://idisk.me.com/mcgroves/Public/pics/stack.jpg

[Starting Small]

Ok so when you stuck the stove pipe in the cinder block holes and pushed them down, how did you open it into the fire to allow the smoke to come out? Did you put in a hold in one of the blocks?

[Groves]

The bottom of our stack is open. It sits (perilously?) on 2 layers of blocks that support the stack from the sides only. Supporting it from the sides leaves the front and back open. We cover the back with more blocks.

http://idisk.me.com/mcgroves/Public/pics/stack/stackb.jpg


http://idisk.me.com/mcgroves/Public/pics/stack/stacka.jpg

[Starting Small]

I see, thank you for putting those pics up. Makes much more sense now. I think if I can scrounge some cinder blocks together I am going to build one this weekend. Looks great!

[DIMariner]

Testimonial to Groves design- I copied it almost exactly and it worked great. Took about 30 minutes to set up (after lugging cinder blocks into the woods) and kept a good boil going. If you follow his pictures, you can't go wrong!

[sams64]

I went with a 9' stack of 6" fitted to a 90 degree square register to make the turn out of the back. Thanks for the tips guys.

sam

[Starting Small]

Question on the block arch. Do you just load the wood in the front and the heat warms the other pans as it is moving toward the stack? I would imagine that you are not tossing wood way down toward the other end. Also, how do you ensure that the smoke goes out the stack and not the front? I am new at this and am sure this is a basic question on arch design. Thanks for your help.

[mathprofdk]

Question on the block arch. Do you just load the wood in the front and the heat warms the other pans as it is moving toward the stack? I would imagine that you are not tossing wood way down toward the other end. Also, how do you ensure that the smoke goes out the stack and not the front? I am new at this and am sure this is a basic question on arch design. Thanks for your help.

Hey SS,

I'm no expert either, and haven't even built mine yet, but I'll give it a shot. The idea of the stack is that the heat will flow that direction (it wants to rise) and once you have the flow in that direction, it will be consistent. You'll have created a draft - kind of like you have to crack a window in winter if you start a fire in your fireplace and your house is pretty tight - the hot air that's rising needs to be replaced by something!

And the reason it's called an "arch" is that you typically build up a ramp of some sort in the back half or so that forces the hot air up against the pans before it leaves through the stack. This way, you have the fire in the front, and then the hot air is forced past all your other pans with a relatively small space before exiting.

Hopefully that helps. (And hopefully it's right!)

~DK

[Starting Small]

I appreciate that, makes alot more sense now. So the idea is to basically push as much hot air as possible through as small a space as possible. I never completely understood why they called it an arch either. Thanks for your help!

[Groves]

So the idea is to basically push as much hot air as possible through as small a space as possible.

Don't lose sight of the basic facts.

You're trying to heat sap. You're trying to heat it quickly, and you're trying to use the least amount of fuel.

The small space is only helpful if it increases the heat transfer to the pans. Often times it does because a lot of hot air could pass under the pan area and escape out of your flue without helping you.

The small space forces it to touch the pans and thus transfer some of its heat to your sap.

Outside of the heat transfer there's no benefit to the small space.

[Dan]

Hey Groves,

Was wondering if you use a door of some sort on your block arch?

Whats the spacing from bottom of back pans down to arch?

Is your opening for chimney in the back wall about a block in size?

Reason I ask I went from last year 4 pans boiled nicely all 4 to 5 pans and lost a little on the evaporation. Went from about 3" under the pans to 1-1.5"? Also might have restricted incoming air to much and filled in back chimney to much? Here's a picture of last year and two of this years setup. Thanks Dan

[Starting Small]

Ok, so I put together my block arch today and tried to start evaporating. I was not able to get the smoke to go out the pipe out the back. Should I make a door to stop the smoke from coming out the front, if so how can air get to the fire to keep it lit? I now have a bunch of ash in the pans. It is the same setup as shown earlier in this post. Perhaps this is fire making 101?Thanks!

[Starting Small]

May I also add that I am only using 2 pans and it is 2 blocks high. Not sure if that would matter. The 2 pans are 12 inches wide each.

[Kev]

sounds like you are not getting any draft started up the flue pipe.
how tall is your pipe?
try several crumpled sheets of newspaper at the very back. have you fire laid with lots of small kindling, so when you do light it, it burns quick and hot.
then light the newspaper, when air is sucking in the front good, light the wood.
the newspaper will start your draft up the flue, the fire should continue it
if you can close up the top of the front of the arch it will help force the draft continue to the back and up the flue

[sams64]

Second the news paper at tyeh back of the bottom of your stack idea. I didn't need to use it, but, that's what I had in my back pocket as an option if needed.

You will certainly need some type of door in front to restrict air flow in to the firebox as well. I use a chunck of 1/8" steel that I cab slide back and forth to adjust teh draft once it is up and running.

Sam

[DIMariner]

Hey Groves,

Was wondering if you use a door of some sort on your block arch?

Whats the spacing from bottom of back pans down to arch?

Is your opening for chimney in the back wall about a block in size?

Reason I ask I went from last year 4 pans boiled nicely all 4 to 5 pans and lost a little on the evaporation. Went from about 3" under the pans to 1-1.5"? Also might have restricted incoming air to much and filled in back chimney to much? Here's a picture of last year and two of this years setup. Thanks Dan

Nice rig. I especially like the arch in the back- true yankee ingenuity (even though you're in MI).

[DIMariner]

Here is the link to the original Groves design (http://matthewgroves.com/Hobbies/Sugaring09.html#2) which has been referenced several times. There are some good views of the stack base as well as the front damper and forced air set up.

SS, I wonder if your fire isn't hot enough to be drawing air? If it is just kind of smoldering it may not be rising up the stack quickly enough to pull air in after it. Cracks between blocks or between pans could also let heat out early and mess with the draft.

[T22A80]

I'm about to build my block arch and it looks like the link to the Groves design no longer works. Does anyone have any pictures?

Thanks!

[Groves]

Well, I'm the Groves, so I can get all the pictures you want. Here they are.

It's been several years since that first design but the only thing we've done is to keep making it longer to hold more pans.

[Groves]

http://img.tapatalk.com/d/14/03/11/ezegugaq.jpg

http://img.tapatalk.com/d/14/03/11/emybenyz.jpg

http://img.tapatalk.com/d/14/03/11/nasy8epe.jpg

http://img.tapatalk.com/d/14/03/11/ehe7e2an.jpg

[Groves]

http://img.tapatalk.com/d/14/03/11/qyvy3aqe.jpg

http://img.tapatalk.com/d/14/03/11/y4aqegu3.jpg

http://img.tapatalk.com/d/14/03/11/edareqyv.jpg

[T22A80]

Awesome thanks! I had figured that's how you did the chimney but the pictures help.

[eustis22]

That thing looks like the Planet Eater in Star Trek - TOS.

[NhShaun]

Great thread! I'm planning on going with this route to save some money, and often see cinder blocks on Craigslist for free.
Has anyone ever tried making a more permanent arch with cinder blocks cemented together, with this general design, and then lining the inside with fire brick? Might not be necessary but i know the blocks don't hold up too well to the heat over time. I suppose then you'd have to worry about pouring a footing to put under the blocks if cement were used for the build. It would be more work for sure, but it would be a tighter unit and hopefully more efficient/hot inside. Just a thought that's been going through my noggin while i try and design my own for this upcoming season.

[FoxHill]

This is my very first post on this great forum, sure to be more.

I'm planning on building a cinder block arch just as we've seen above, this thread more than any others has helped me clarify my design.... for the moment :)

One unanswered question (which was directed to Groves many posts earlier) is what is the distance given between the ramped arch and the bottom of the pans. I plan to use 6" deep pans as well, and Im trying to get a sense here and from other posts just what kind of constriction is too much/not enough to get the heat to reach the pans. I obviously dont want the heat to pass unused below the pans, and likewise I dont want to rear-most 6" pan to overly constrict airflow to the chimney. any thoughts on this...

[Schiefe4]

http://www.leaderevaporator.com/pdf_files/the_half_pint_evaportor.pdf

Read about the firewall in the link above. This may help clarify your design.

[Groves]

Groves here.

It's a balance between keeping the heat up by your pans and restricting the airflow.

I would use your combined chimney area to give yourself a minimum area to have below the pan bottoms.


ONE thing that I do that may be helpful to you is that I use a 4inch pan for the pan closest to the stack. This lets the ramp take shape while keeping a more uniform cross-sectional area below my pans as it approaches the stack.


Keep us posted!

[FoxHill]

http://www.leaderevaporator.com/pdf_files/the_half_pint_evaportor.pdf

Read about the firewall in the link above. This may help clarify your design.

Thanks!! I sure just learned a lot about the Half-Pint (which is on my list of topics to read up on) however I cldnt pull from that pdf what I am puzzling over, regarding distance between the ramp and the pans...

[Schiefe4]

I don't think there is a ramp. There is a firewall and that is 8 1/2" away from the back of the evaporator.


1. You will need 16 full bricks and 6 half bricks.
2. Cut bricks for the locations as labeled
a. FW1 – full brick cut to 4” x 4 ½” (4 needed)
b. FW2 – half brick cut to 4” X 4 ½”
c. Cut one half brick in half (results in 2 pcs 4 ½” X 4 ½”) (HHB)
d. Cut one full brick in half (results in 2 pcs 4 ½” X 4 ½ “) (HFB)
3. Place a pencil mark 8 ½” in front of the face of the back wall brick. This is the front of the firewall.
4. Place bricks in the arch as illustrated. The bricks are laid with the 4 ½” side down. Only the surfaces of the brick
where they face another brick need to be coated with cement.
5. Fill all edges and gaps with cement.

And depending on how big you make this block arch, I'm not sure that you are going to want/need a ramp.

I think I understand the question now... looks like 2 1/4'" from the bottom of the pan to the top of the firewall...

[FoxHill]

Yeah that's what I think I cld see from the photo. I like the idea of the 4" pan as well... Thanks both of you!