Building a cinder block arch next weekend. Questions!

[Loun]

- What is the optimal height from grate to pan bottom?

- Do I need to build a frame to hold the pan or can I set it on the left and ride side walls? (maybe 2 inch either side)

- Is there a more benefit to having a slant or an actual arch in the back side of it? Air accelerates over a curve however I dont know if it would matter enough for this application.


Thanks everyone!

-Lou

[KenWP]

Seems that 18 inchs is the height from the grate to the bottom of the pan in the firebox. Give you room to make a pile of wood to burn and for the flames to reach the pan at the right section ofthe flame. Most archs seem to have a slant from the front to the back before getting to the chimney. you could curve it but how your going to build a curve is the guestion.

[Loun]

regarding the curve. I was going to cut out the inside section of a 55 gallon drum. Its precurved, then I would start flattening until it was the right length / curve. I may use the lid of the drum with a hinge as the door as well.

Thanks for the estimate on the height!

[C.Wilcox]

Loun,

What size pan are you using?

The purpose of the arch is to force the heat up against the bottom of the pans. If you don't have one the heat can short circuit and go up the chimney without ever touching the pans. Your 55 gallon drum should work fairly well, but things get HOT in there so don't be surprised if it sort of deflates over the season. As far as resting the pan on the blocks, that's what I did, but keep an eye on the blocks. They're going to split and crack from the heat and might get a bit unstable over the course of the season. Shouldn't be an issue, but it's something to keep an eye on.

[WESTVIRGINIAMAPLER]

I have close to 24" and wish I had more.

[Loun]

As of now I have a 2x3 pan on order but might be upgrading that to 2x4 tonight depending on what the time table will be for the larger pan. It has a preheater on top.

Next year my arch will be setup a lot better but since i dont have a ton of time this year I need to make due with what I have. As for it deflating, I was contemplating using cinder blocks to help maintain some of the shape. Or packing dirt behind it. wast sure which would insulate it better, dirt or a stagnant air barrier.

I tend to overthink things.. ;)

[TapME]

Lou look at the pics in my photo book at the concrete arc that I use it should help you figure things out.

[Loun]

TapMe - Thats essentially what I had in mind except I was planning on putting a bottom layer of cinder block so I was going to be 1 more layer of block higher. It looks like your pans are on a stand? thats what im trying to figure out now. I can try to get someone to build me a stand but currently I dont have one.

Whats on the bottom of yours? Brick? just dirt?

[TapME]

it's dirt cheep. I made the slant with brick and filled in the rest with dirt. I also used brick on the sides to save the blocks from the heat. The fire box is only 16'' tall and it work well for me. If it was taller it would make moving the ash every other day instead of every day. Have fun this maple thing is a blast. Last year I made a metal frame to sit the pans and stack on with some leveling bolts welded on, and it made it easy to set the pans back to level after the ground thawed.

[Big_Eddy]

2 rows of 8" standard blocks. On the first row I turn the front 2 blocks sideways so that there is about a 4" gap between for air to enter, then build the walls 1" closer together than my pan is wide. I make my arch 10" longer than my pan, as I have a flat plate I put on the rear for the stack. It's important to get the base level. I find a pail of gravel or sand a great help - I can tilt up one side and add a bit to level things out. The second row is staggered over the joints as usual.

I have a 20" x 16" grate that sits up about 6" inches, then behind I fill in the arch with whatever chunks of broken block and rock I have to about 4" below the top. When I remove the ash it gets tossed back there too. Rough is better than smooth - it causes turbulence in the gasses and forces them up to the pan. I don't bother with fire bricks. I lose a couple of blocks every year, but I take it down and rebuild it every season anyway, and the larger rubble fills the cavity next season.

My stack sits on a 26"x10" plate of 1/4" steel with a 8" hole in the middle, surrounded by an 8" ring of 1x 1/4" flat bar. The plate sits flat across the blocks behind the pan. I use about 12' of stack and 3 guy-lines to keep it up. An old piece of sheet metal for a door.

In my setup, I have about 10" above the grate, and usually fill it with wood. For this season (if I don't finish my evaporator) I have been considering using 3 rows of blocks to increase the height, still filling the rear with rubble. 10" is enough space for wood, but the flames travel backwards, not upwards to the pan, and the front does not get as much heat as I'd like. Adding height could be a problem though, as I will then need to lift my tank platform the same amount.

[Grizz747]

My block arch is 3 blocks high. In the back I lay the middle block on its side and 2-3 more towards the fire for a draft. Then a wall straight up and fill in behind the wall(on top of the blocks with dirt) This year I am going to add a fan from a gas hot water heater to force the draft and I am also using a 27" x 48" divide pan(last year 4 steam tray pans). I went with this size as next year I am planning on using a fuel oil tank as my arch. See the pictures on my link below.

http://www.flickr.com/photos/47018155@N08/

[Loun]

My plan has me making a cinder block floor and then covering those blocks with fire bricks. This is going to cost about $60 or so. I see a lot of peoples cinder block arches are using an earthen floor with no fire bricks. Will I see enough efficiency increase to make a block and brick floor worthwhile?

If im going to do something id like to do it as "right" as possible within reason :)

[WESTVIRGINIAMAPLER]

Might increase efficiency a little, but if you are concerned with cost, I don't think it would be worth the $ 60. Heat goes up, so you are not going to gain very little by putting them under the fire.

[Grizz747]

Loun
I built mine on the ground. The 3 extra blocks were for a draft and it worked great. I built a wall on top of the block closest to the fire to force up the flames and filled in behind it with sand(I live by Lake Erie and it was the right price:) .