gt40's Pompeii Oven 42" build log

[brickie in oz]

Re: gt40's Pompeii Oven 42" build log

In this type of design the heat of the dome is supposed to increase the draw pretty dramatically,

Wouldn't a vertical flue draw better rather than the smoke having to do a 90 degree turn?

[shuboyje]

Re: gt40's Pompeii Oven 42" build log

If all else was equal a straight vent with a nice gradual taper would certainly draw better then one with drastic bends in it, but if the theory behind this type of vent is correct, all things are not equal. Stack effect is the driving force behind the draw in our ovens, and as I am sure you know it is based on temperature difference and the volume of air. This type of vent design puts the hottest part of the oven in the path of the flue gases and drastically increases the temperature difference between the flue gases and the outside air thus drastically increasing the draw.

I'm pretty confident on the theory of how it works, now I curious to see how drastic the difference really is.

[brickie in oz]

Re: gt40's Pompeii Oven 42" build log

Ive clocked my flue gasses passing the damper slot in the chimney and they are around 1000c, the roof of my oven gets to 600 to 800c so the roof of the oven being cooler will in theory cool the flue gasses rather than heat them.

[shuboyje]

Re: gt40's Pompeii Oven 42" build log

Uno Forno, handmade brick ovens by Stefano Ferrara.

Since it has gotten so much talk this link shows a traditional vent.

[gt40]

Re: gt40's Pompeii Oven 42" build log

I made a bit more progress - dry fit the recirculating chimney.

Dry fit pic:



I also cleaned my dome finally. My daughter did a first pass with a scrub brush and water. I followed up by going inside with an angle grinder and 40 grit. I wore dust proof goggles + respirator and ground the surface while stopping when the dust was too thick to wipe the dome with a wet rag. You cannot believe how much dust an angle grinder makes in the confined space of an oven.

After that, I followed up with 50% muriatic acid/water mix sprayed from outside the dome and washed everything down really well to neutralize things. I dried things with the leaf blower and here you go:



My strong advice is to take the time to clean each and every course as you go and not do what I did :P

[gt40]

Re: gt40's Pompeii Oven 42" build log

UPDATE: I finished the oven.

Recirculating chimney was finished and I am just waiting for my chimney tube to arrive. I can't wait to start curing fires but will try to be patient. I have 3 rolls of fiber insulation ordered and then will build a house around the oven.

I really am looking forward to observing how the draw is and second, how hot is it the next day after I insulate it.

A few more pics:







Thanks for looking

[benguilford]

Re: gt40's Pompeii Oven 42" build log

That is the most creative chimney I've seen to date! Well done, looking forward to hearing how the first firing goes

[Les]

Re: gt40's Pompeii Oven 42" build log

GT,

I forget why you did the vent this way. It looks very cool (and clever) but appears to be excessive work.

[gt40]

Re: gt40's Pompeii Oven 42" build log

GT,

I forget why you did the vent this way. It looks very cool (and clever) but appears to be excessive work.

I am thinking the same thing almost now that it is finally done. It ended up being a mini project in itself.

To answer your question, I had extra bricks basically. This was a big oven with a 49" floor and I erred on too many bricks buying 450. I finished the basic dome and chimney foundation with 400. That left me with 50 more bricks and it seemed to me that if you recirculated the hot air over the dome, maybe it would heat up faster as the hot exhaust from the oven is in contact with the dome from the inside and the outside.

I have seen some masonary heaters with recirculating channels to capture more heat into the central mass and it kinda made sense.

The other thing is I am gaining 3 feet of chimney before I even go vertical so I hoped for better draw. The final thing that pushed me over to do all the extra work was the MHA oven design I stumbled across:

MHA News - 2006 Meeting - Backyard Oven with Peter Moore

[Les]

Re: gt40's Pompeii Oven 42" build log

maybe it would heat up faster as the hot exhaust from the oven is in contact with the dome from the inside and the outside.

Awesome - sounds reasonable to me. James may be making an edit to the plans.

[david s]

Re: gt40's Pompeii Oven 42" build log

" I am gaining 3 feet of chimney before I even go vertical so I hoped for better draw".

A horizontal chimney does not create any draw. In fact my Daniel Rhodes kiln bible says "each foot of horizontal must be compensated for by 2 additional feet of chimney"
So make it taller than you think it should be.

[chidding]

Re: gt40's Pompeii Oven 42" build log

" I am gaining 3 feet of chimney before I even go vertical so I hoped for better draw".

A horizontal chimney does not create any draw. In fact my Daniel Rhodes kiln bible says "each foot of horizontal must be compensated for by 2 additional feet of chimney"
So make it taller than you think it should be.

Agreed with above, but really its not perfectly horizontal.. its moreso a 45 degree bend isnt it?

[gt40]

Re: gt40's Pompeii Oven 42" build log

Agreed with above, but really its not perfectly horizontal.. its moreso a 45 degree bend isnt it?

Yeah it is around 45 degrees. I guess we should know in a bit after I get to start lighting curing fires.

If you scroll through the MHA link I posted, they are more horizontal than me and have 2 feet of chimney tile but it seems to give great draw.

[david s]

Re: gt40's Pompeii Oven 42" build log

It should be easy enough to add more if needed.

[brickie in oz]

Re: gt40's Pompeii Oven 42" build log

they are more horizontal than me and have 2 feet of chimney tile but it seems to give great draw.

Lot of soot on that new arch for it to be drawing "great".