oven opening: arch vs straight sides?

[Wiley]

Originally Posted by Archena

Disclaimer: If I knew what I was doing I'd already have an oven...



I suspect the reason is the height/length ratio. To gain length (also called width - confusing in 3d) in a true arch you have to increase the height of the door opening which will eventually cost you in heat retention. The efficient ratio is probably fairly small. With vertical sides the length (width) is obtained without increasing the height of the door opening.

I must have missed something, I understood that the important ratio for the oven to draw well was the height entrance door to the interior height of the dome. I don't recall anything about height of entrance door to the width of the entrance door. I have an arched entrance and find that it works well and is pleasing to my eye. I can see where one could perhaps have an entrance that was so wide that there would be significant loss of heat and so make it hard to get and keep desired temperatures, but I am unaware of any "sweet spot" in the ratio of width of door to height of door. Did I miss something?


Wiley

[Archena]

Probably not - I can't remember now what I was thinking other than you can end up with a large opening volume whereby heat will escape if you keep widening the arch to gain height.

Nevermind... brain cramp...

[sjmeff]

Hi Carlos - I had a follow-up question to the one I posted in your oven building thread, but I thought it made more sense to post it here (rather than hijacking your build thread).

I wanted to ask about the height/width ratio of your entry arch. Since it appears to be a true half circle, is the height roughly equal to the width? In your posting above, you mentioned that you were aiming to have the dimensions roughly equal to what the FB plans call for (20" wide, 12.5" high); is that approximately where you ended up now that you've built it?

It seems like it would be easier to get more height out of the arch, if needed, by simply putting standard square bricks at the bottom to raise it up, but getting more width in a round arch seems like it would be difficult (since, presumably, it would weaken the center of the arch to add a brick for width).

Hope that all makes sense.

Thanks again!

S

[carloswlkr]

Stephen,
I did exactly as you suspect. I added a bit of height to my arches by laying one standard brick on its side to start each course. I used a 10" radius to draw the circle, which gave me 20" of width, and would have given only 10" of height. I raised it up 2 1/2" with the addition of the rectangular fire brick, so my final internal height is now 12 1/2" and the width is still 20". The outer arch is 23" wide, if I recall correctly, using an 11 1/2" radius to draw my arch, with a top height in the center of 14".

Good luck!

[sjmeff]

Seems obvious in hindsight, I guess I just needed to talk it through. I remember far too little of rudimentary geometry. : )

[carloswlkr]

No worries! That's what the forum is for!