How high should the back of a firebox be?

[Friar_Athanasius]

I bought an arch from GBM and one of its peculiar qualities is that the firebox doesn't have a back wall (see the picture). It is supposed to just have a mound of vermiculite in the back to angle the heat upwards towards the chimney but I do not like that at all. I am having a sheet of steel made to make the back of the firebox and I would like to know what the vertical height should be that would make good draw - like how far from the top should the back of the firebox go?

http://bayimg.com/hAEFJaadF

[cpmaple]

What kind of pans it makes a differents and will it ramp to the chimney this wall or does it already have the ramp?????

[Friar_Athanasius]

There is a ramp but what is supposed to be done with the present design is that you make the ramp from vermiculite insulation. What I am planning to do is to make the back wall for the firebox, put the vermiculite behind it to ramp it up towards the chimney and then put arch board and then fire brick on top to make a solid ramp instead of having just a pile of insulation.

[Dave Puhl]

mine is a raised flue ...I fire bricked it right flush to the bottom of the pan/top of the arch .....you want the fire/heat to get up into your flues...force as much heat up to your flue pan...my back wall is straight and after that the vermiculite lays behind it and is covered by old slate siding to hold that fluffy stuff in place...

[Flat47]

Your picture isn't opening, so it's tough to tell what is going on here, and it seems like terms are being mixed.

Your arch has sheet metal on the bottom (except under the grates), right?
And, you've got sheet metal running up-slope from the grates towards the back of the arch (aka "ramp"), right?

Then all you need to do is line the arch with brick (search the forum for "bricking") and add vermiculite or sand. Vermiculite has been used for a long long time to close the space between the bottom of the arch and the bottom of the flue pan. Sand can be used, too, but it adds a bunch of weight.

[Friar_Athanasius]

Well it seems I can't get pictures to work!

I do have a "ramp". The ramp goes from the edge of the grating on which the fire sits. Seems to me there should be a wall - as I have seen in other evaporators - separating the firebox from the ramp. I am planning on filling up the ramp with vermiculite and then just setting bricks on it to keep it down but I would like to know how far up to make the barrier between the firebox and the ramp so that I have the best draw.

Trying the picture again...
http://s1126.photobucket.com/albums/l620/Friar_Athanasius/?action=view&current=P3080034.jpg

[sbingham]

We had a GBM 2x4 for the past 5 seasons. I built a wall at the back of the firebox with full fire bricks, filled up the void with vermiculite and covered the top of that with a layer of ceramic blanket.
It worked OK but, I am much happier with the design of my new WF Mason unit.

I built it up to within 3-4" of the bottom of the pan {flat pan} then sloped it up from there with the vermiculite to the stack.

[Maple Ridge]

CPMAPLE is right. Do you have a raisd flu or a drop flu pan. I have a new maplepro evaperator which I installed this year. The plans say leave 1/3 of the pan befor the wall, and leave 8" from the base of the stack. Fill the area with sand etc. The problem I had is when I fireed it up. It sounder like a fraight train and I could not get the front pan to boil. I called the manufacturer (they were very helpful) and they told me to only leave 1 to 2" between the base of the stack and the bottom of the arch. This cut down on the draft. So if it is a raised flue, 1/3 of the pan will be exposed, and 4" of the pan will be exposed in the rear to allow for draft with only 1 to 2" drop behind the back wall. I hope this isn't too confusing. Also there should be a manual to explain this. After I talked to the manufacturer, he told me he would fix the manual to explain it better.

[Friar_Athanasius]

We had a GBM 2x4 for the past 5 seasons. I built a wall at the back of the firebox with full fire bricks, filled up the void with vermiculite and covered the top of that with a layer of ceramic blanket.
It worked OK but, I am much happier with the design of my new WF Mason unit.

How far up did you build the wall, that is what I would like to know.

[Friar_Athanasius]

CPMAPLE is right. Do you have a raisd flu or a drop flu pan. I have a new maplepro evaperator which I installed this year. The plans say leave 1/3 of the pan befor the wall, and leave 8" from the base of the stack. Fill the area with sand etc. The problem I had is when I fireed it up. It sounder like a fraight train and I could not get the front pan to boil. I called the manufacturer (they were very helpful) and they told me to only leave 1 to 2" between the base of the stack and the bottom of the arch. This cut down on the draft. So if it is a raised flue, 1/3 of the pan will be exposed, and 4" of the pan will be exposed in the rear to allow for draft with only 1 to 2" drop behind the back wall. I hope this isn't too confusing. Also there should be a manual to explain this. After I talked to the manufacturer, he told me he would fix the manual to explain it better.

The pan I have is a flat pan with separators. The pan sits on the top of the evaporator and no part of it hangs lower than the other. I hope that answers the question.

[len]

Select the paperclip/ "attatchment" icon when posting/ editing, and you can upload a *.jpeg from your computer (or web site "url"). There is a max file size that you can't exceed, either resize/ edit it (scale down), or reset the camera file size parameters lower as an alternative.

BTW, the image icon is just for a website url, which just links that site to this site through http (hypertext transport protocol). The attatchment icon does both upload, and url coding.

[Flat47]

No, for attaching pics, use "Manage Attachments" tab on the "advanced" reply screen to upload and attach a pic.

Friar,
I think you are over complicating things. You don't need to wall off the ramp. The ramp is intended to create a draft. Just run it, see how it boils, and then refine your set-up. I think you'll find that it boils quite nicely as is.

[len]

No, for attaching pics, use "Manage Attachments" tab on the "advanced" reply screen to upload and attach a pic.

Friar,
I think you are over complicating things. You don't need to wall off the ramp. The ramp is intended to create a draft. Just run it, see how it boils, and then refine your set-up. I think you'll find that it boils quite nicely as is.

No, as if incorrect? Under quick reply, then perhaps, but select Post Reply (at lower left side), and my advise is valid. Perhaps this is just a clarification- but No suggests wrong, and is incorrect.

[Friar_Athanasius]

Ah, there we go, now there's a picture!

[Friar_Athanasius]

[QUOTE=Friar,
I think you are over complicating things. You don't need to wall off the ramp. The ramp is intended to create a draft. Just run it, see how it boils, and then refine your set-up. I think you'll find that it boils quite nicely as is.[/QUOTE]

Won't some of that vermiculite fall into the firebox?

[Maple Ridge]

FRIAR
Running a flat pan, I would think you would need a fire wall. I would also install backer board and a layer of brick up the incline. Your fire wall will need to be back far enough so that the flame will cover the bottom of your pan. You will need to leave enough room between the pan and wall to allow for draft. I am sure you will be making adjustments to the height until you get the right draft. I would just stack the bricks until you are ok with it.

[Flat47]

Won't some of that vermiculite fall into the firebox?

Very nice job bricking - looks great!
I would brick the ramp just like you've done on the sides (arch board under split bricks), and at the point where the ramp tranitions to horizontal, stand your bricks upright on edge or end (which ever works best) to make a lip. Do the same near the stack collar, and you've made a "pit" of sorts to fill. Lay arch board on the horizontal metal, then fill with vermiculite or sand. If you're using forced draft and find that the vermiculite is getting blown around, you can lay some split bricks on the vermiculite.

[Flat47]

No, as if incorrect? Under quick reply, then perhaps, but select Post Reply (at lower left side), and my advise is valid. Perhaps this is just a clarification- but No suggests wrong, and is incorrect.

You're correct. I didn't understand. Clicking on the paperclip takes you to "Manage Attachments." Sorry.