Adding a grate to a block arch - need your input.

[jimmol]

I had a small steam pan block arch, 25" long and 20" wide which I modified to hold an 18" by 34" continuous flow pan from Silver creek. (Pictures below) I have two 4' stacks through the cinder blocks and plan to reduce to 2" below the pan. The stack throat narrows to 14" across before turning up to the stacks.

Currently, the firebox will be 16 by 14 after the firebricks go in and 14 deep. Does that seem adequate? Any reason to make it deeper? Maybe smaller?

Thanks to all who take a look and especially those who share their years of experience with us.

PS

This forum has too much information... This was originally a post asking about adding a grate to a block arch.

I had some questions about adding a grate since, after skimming through numerous articles about block arches, continuous flow pans, evaporator pan sizes and the like, it seemed like adding a grate and air from the bottom would be an easy way to increase boil. Then, in searching for how to add a profile picture, the search turned up this tread:http://mapletrader.com/community/sho...ency&highlight. Kind of adds a different light to the whole air from the bottom idea.

So what I was going to ask, no longer needs to be asked regarding the grate. But if you have an opinion about adding a grate to a block arch, please share it.

[ecolbeck]

I wouldn't hesitate to add a grate to any arch. It will definitely increase heat output despite the known inefficiencies of the design. Air under fire (AUF) is used because its the simplest and cheapest way to get a hotter fire. The craftier members of this forum have made air over fire designs (AOF), similar in concept to modern efficient wood stoves. There is tons of information to be found on that topic in these forums. The issue I ran into with grates on a block arch was finding material that could withstand the heat, particularly with a blower. The fireplace grates that I used on my block arch melted after one season.

[TapTapTap]

Yes, you want grates to allow airflow from up below your fuel.

And, I should mention that grates can be expensive. I'm embarrassed to say how much my 30"x8" replacement grates cost. But I'm confident that just a plain piece of steel angle iron won't hold up to the intense heat.

[eustis22]

angle iron will NOT stand up to the heat, even if you do make it a V. See if you can find 2 inch square tubing from a local salvage yard or metal supply. It will last much longer and be cheaper than a sturdy enough grate would cost.

[buckeye gold]

I have had angle iron grates in my arch for 10 years and they are fine. when I extended the firebox I added 3/4" bar stock and it does fine too. Heat goes up and added air under fire should initially cool the grates some. I would not be afraid of good heavy angle iron. Now it added some 3/4 bar stock in the top of my box to support brick and they drooped from the heat.

[jpcole]

I switched to angle iron grates about three years ago and won't use anything else. The cast iron ones only lasted 1-2 years after they were flipped because they droop and burn up. The ashes fill the V and the AUF will help them last a lot longer without having to flip them. Don't go cheap, use 1.25x3/16 angle or larger. It will last.

[Cjadamec]

Angle iron grates work really well. With AUF and when they fill with ash they will last many years. You don't even need heavy steel. Mine is made from a cut up bed frame and after a lot of use it still looks like the day I made it no sagging or warping at all.

Another user made his grate out of steel wire fence posts which are very cheap and easy to get.

Either way adding the grate under the fire is definitely worth it.

[maple flats]

You can not compare heating a house with boiling sap to make maple syrup. They are a universe apart. To heat a house you try to burn the least amount of wood you can while extracting the heat needed to heat the home. When making maple syrup you try to get the boil to be a hard as you can get.
This is not so you can brag about your gallons per hour (GPH) but the faster the boil the better the syrup and the less time you need to be boiling. In heating a home you might just add wood every 6-8 hours, maybe even 12 hrs depending on the stove, but in boiling sap it is very common to add wood by using a timer, just to keep it uniform (I add wood every 8 or 9 minutes when boiling without visitors and with visitors there I change it to 10 minutes sometimes.
A grate will help you get a faster boil. Good combustion needs good air flow. Boiling faster needs good combustion.
If you want to save wood, read all of the things you can about evaporator efficiency on this site and look up "combustion efficiency " on the UVM site. Much of it will not work for a temporary block arch but some might help. A grate will help, but if you can somehow get more air in blowing down from above from the sides can improve the efficiency.

[TapTapTap]

I agree that the steel angle iron option should work in smaller arches. I have a 30"x10' Leader Vortex Arch with 2 separate blowers. It's like a blast furnace! Therefore, I chose the manufacturer's cast grates even though I have free access to very heavy angle (as big as L6x6x3/4).

[jimmol]

...A grate will help you get a faster boil. Good combustion needs good air flow. Boiling faster needs good combustion....
A grate will help, but if you can somehow get more air in blowing down from above from the sides can improve the efficiency.

A grate it is, now how large a firebox?

Two things stood out as I read though the Thread referenced in the first post. First, the talk was about adding blowers to introduce air into the arch. A friend once had a wood stove, 16 x 30 free standing. It had one tube along the length. After the fire was going, if you dampered down the air intake, this tube would supply air and you would see flames during out side each hole. The heat increased about 25%. No blowers needed.
Second, my block arch, due to the limitation of the twin 4" stacks, would start smoking around the pans and upper block joints if I opened the front air wide. As soon as I closed it up the smoke stopped, if I closed it more, the boil kept going. As I look back, was it because of the air bring sucked in where the smoke was going out - above along the top. Maybe that's why it got some good boiling going.

I am going to run a 1/2" ceramic blanket around the inside and the firebrick (stacked for now) over it where I can. This should cut heat loss into the block and reduce the air coming in between the blocks. I am also going to run an angle iron frame around the pan and set it atop one ceramic blanket or flat fire gasket, to help seal it. I may leave some gaps up at top to draw some air in as it runs. I will work on it in the summer and change what is needed. I need to finish it up before the next cold snap.

So what would be the best firebox size?
Firebox small.jpgLarge Firebox.jpg

This is current size, 11 x 14. Grate is cast iron, 7 inches by 16. The grate is touch the front inside of the firebox (bottom). At the top is a 4" block I can remove to make it larger. 15 x 14" I have a second grate to add next to the first.