Custom Made Outdoor Firepit/Fireplace - Some Opinions Please...

[Kustrud]

Alright, I built this thing from scratch for a large outdoor heater/fire that you can enjoy without getting all smokey like from a regular campfire. It's all built from 30" propane tank parts so it's 1/4" steel. The "chimney" is 1/4" steel as well and 6" ID pipe. The whole thing is extremely sturdy and I don't think a tornado would even blow it over. I do have a couple of questions:

1. Should I add supports about 18" up the pipe welded to the exterior of the base in 3 sections? Would the top of that being hot lose enough strength to worry about it sinking or shifting eventually? The pipe probably weighs 150 lbs. I think it's fine but it is a thought I had.

2. My goal was to run this without a door at all, but it does belch some smoke out the front which I do not want at all. It drafts hard enough to float a beer can in the chimney while running instead of it falling down into the fire. It works perfectly and puts off crazy heat, but I don't want any smoke out the front. To mitigate this, I built the door and used some SS screen. It can be smoking like a train and when you close the door, zero smoke out the front - works perfectly! I realize this is because I essentially "shrank" the size of the opening thus increasing the velocity of the air entering. But, I just like the looks better without it as nothing blocks your view of the fire
. Any ideas here? I looked at our fireplace inside which has a much larger opening and we never get any smoke out the front of it. I noticed that it does have a lip on the inside across the top that runs straight in towards the fire probably 4" or so. If i built a lip inside the opening like this that ran around the circumference of the opening and went towards the inside 4" or so would this force any smoke back towards to center and then get sucked up instead of just spilling out the front? Open to ideas here to get this to work without the door.

I realize this is not a "wood stove" perse, but it's similar and you guys are knowledgeable with draft, etc.

 

[kborndale]

6" pipe is not large enough for an open fireplace.

 

[Kustrud]

6" pipe is not large enough for an open fireplace.

I was torn on going with a 6" vs an 8". This is where it gets confusing....does it work with the screen door simply due to the increased velocity of the air being drawn in?

Do you think it'd work fine without the door with an 8" pipe?

Really looking for some ways to prevent smoke spillage as-is without changing chimney size if possible. Lot of work to do that lol!

 

[EatenByLimestone]

Make the opening smaller.

 

[Kustrud]

By making the door with the screen that’s essentially what I did, make the opening smaller.

I switched the screen out to some thicker/nicer stainless. It seems to radiate heat more out the front now. I’m happy with the door! Turned out pretty slick!

It puts off some great 360 heat being so thick!

Video attached is after throwing a bunch of oversized a not even greatly seasoned wood in there. Shut the door and it just takes off. Pretty impressed.

Ya’ll think the weigh of that pipe on the top is OK without extra support?

 

[Kustrud]

Another question on this, still really want the option to run it with the door open. It'll be a lot of work but it'd be worth it. An 8" diameter flu has almost twice the area of a 6"......If I swap the stack from a 6 to an 8, do you think that would stop smoke from spilling out the front with the door open?

 

[Ryan_C]

Bigger flue can help, but draft geometry usually matters more. The flue cross-sectional area should be about 1/10 of the firebox opening area (for a round flue). Firebox depth is typically ½ to ⅔ of the opening height — too shallow and smoke rolls out.

You also need a properly shaped throat and smoke shelf / throat to guide flow smoothly into the chimney and reduce turbulence and downdrafts. Poor transition geometry causes spillage even if the flue is oversized.

Chimney height is also a factor in draft strength.

 

[Kustrud]

Bigger flue can help, but draft geometry usually matters more. The flue cross-sectional area should be about 1/10 of the firebox opening area (for a round flue). Firebox depth is typically ½ to ⅔ of the opening height — too shallow and smoke rolls out.

You also need a properly shaped throat and smoke shelf / throat to guide flow smoothly into the chimney and reduce turbulence and downdrafts. Poor transition geometry causes spillage even if the flue is oversized.

Chimney height is also a factor in draft strength.

Appreciate the reply, this is what is interesting to me.

- The opening in the front is about 210 sq. inches.
- 1/10th of that is 21".
- A 6 inch pipe has an area of 28 inches sq. and an 8" has 50 inches sq.....that's why I went with the 6". However, on the flip side
intrigues me as that is quite a big difference in the flu size if I were to change it.
- The body of the fireplace is a 30" wide/deep circle, so plenty deep.
- The geometry is also perfect in the fact that it is a smooth finish inside and also a nice tapered dome straight up into the chimney like a funnel. I was honestly shocked that any smoke comes out of the front.

I've tried numerous things such as holding cardboard in front of it to shrink the opening, using the door I made with the stainless screen, etc. and all of these methods work by stopping the smoke spillage instantly. The problem with shrinking the opening is the direct heat loss out of the front as well as blocking the view of the fire. So far, the door with the screen is by far the best choice. But number 1 would be able to just run it without a door, so I am trying to figure that out. Even just that screen door blocks a lot of heat you can feel once you open it.

It must be something with turbulence inside, how wide the body is, etc. There is something that I am missing that to me should be an easy fix once I figure it out. I've really enjoyed tinkering with this though, it's been a lot of fun!

Really do not like the idea of trying an 8" pipe as that involves finding a pipe, a lot of cutting, a lot of grinding, and a lot of welding lol! I'll do it for sure but that's last resort.

Anything else I'm missing or you could think of??

Going taller with the "chimney" is not an option. I don't think it needs to be either, it's basically just a giant, super-thick chimenea.

 

[bigealta]

You could just add a single wall 2ft, 3ft or 4ft piece on the top of the pipe just to see if it helps. If it does does screw it in. Easy fast and cheap.

Also maybe you could make a hinged perforated stainless partial door. Hinged from the top so you can lift up to load and then either leave it propped open or close it and have the bottom 1/2 open and top 1/2 closed.

Or just cut out the bottom 1/2? of the stainless panel in the door?, or some other percentage.

 

[Kustrud]

You could just add a single wall 2ft, 3ft or 4ft piece on the top of the pipe just to see if it helps. If it does does screw it in. Easy fast and cheap.

Also maybe you could make a hinged perforated stainless partial door. Hinged from the top so you can lift up to load and then either leave it propped open or close it and have the bottom 1/2 open and top 1/2 closed.

Or just cut out the bottom 1/2? of the stainless panel in the door?, or some other percentage.

THIS! This was my next idea. I'm going to get another piece of SS mesh and hold it in place so I can find out how much bare opening I can have at the bottom before allowing smoke out. Then I'll cut and re-weld the door frame making the door a partial door hinged from the top for loading. I'll play with this soon when I have some time.

 

[bigealta]

On our coal forges we had removable metal 1/3 circle "awnings" that just hung on a hook above the rounded opening at the top of the forge smoke box opening. You could try that too.

 

[Kustrud]

On our coal forges we had removable metal 1/3 circle "awnings" that just hung on a hook above the rounded opening at the top of the forge smoke box opening. You could try that too.

Interesting - could you find a picture of this somehow? I think I know what you're saying but cannot quite get it...

 

[Kustrud]

Alright, took the screen out, redid the hinge design, added a handle, and kept adding metal in the front until the smoke stopped coming out! I like it! Ran out of welding wire, but got everything tacked in place at least.

You can feel the heat out the front now as if it were open. Crazy how much heat that screen blocked.

 

[bigealta]

I tried to find a pic but no luck. I like what u did here.

 

[Kustrud]

 

[bigealta]

Nice, this one is the best version.

 

[bigealta]

Our forge had the hood similar to this but ours was removable and did not go down the sides like this one.

 

[Kustrud]

I just had an idea, I'd probably still keep the door. But instead of going from a 6 to an 8" pipe what if I used some thick walled 2" pipe and added 3-6 "collector" style pipes feeding into the chimney 12" up or so. I cannot figure out the science behind this, but wouldn't that be the same as using a big 8-10 collector feeding into a 6" pipe? This would look incredibly cool adding some character too I think!

Main thing, would that technically increase the draft??

Rough idea below...

 

[stoveliker]

That would decrease draft, as you'd be "satisfying" the "suction" created by the warm gases in the pipe, by sucking in air through those side-entrance pipes, rather than through the firebox.
You'd get more smoke roll out.

Same as why you need to have no leaks in your stove pipe and flue piping for your in-house wood stove.

 

[Kustrud]

That would decrease draft, as you'd be "satisfying" the "suction" created by the warm gases in the pipe, by sucking in air through those side-entrance pipes, rather than through the firebox.
You'd get more smoke roll out.

Same as why you need to have no leaks in your stove pipe and flue piping for your in-house wood stove.

In my image I meant to illustrate that the collector pipes would be attached to holes in the lid so they would be “sucking” from the firebox as well.

Does that make sense?

 

[stoveliker]

Ah, ok. Missed that.
That won't decrease draft, but it won't increase it measurably either.
The impedance of these smaller dia tubes won't help your case.

But If you like the view, go for it. It won't hurt anything.

 

[Kustrud]

Ah, ok. Missed that.
That won't decrease draft, but it won't increase it measurably either.
The impedance of these smaller dia tubes won't help your case.

But If you like the view, go for it. It won't hurt anything.

Thats what I figured, thanks! The area of those smaller pipes doesn’t add up to much difference.

I think to have the option to run it smoke free with the door open I need to find an 8” pipe.

Couple 1/4” thick 8” pipes close by. I’ll have to grab one and get cutting!

Not sure if I want to try all that work or just leave as is…..

 

[bigealta]

you could mock up a tin "Test" hood Like in the forge pic i posted, and just hold it in place with tongs and see if that helps.