Vent Opening Size and Construction

[lhuhn]

I am starting to think ahead to the vent design and construction and have a few questions and I can't find the answers in other threads.

First, is there a vent opening size ratio? In other words, if I am building a 42" high dome oven (and I am) and use the opening size of 20"x12.5" as recommended, do I need a vent opening size of ? square inches?

Second, if I opt for the concrete vent construction do you need a special concrete mix or just basic concrete mix?

Thanks in advance

[ThermoJax]

I think you take the square inches of the inner arch and use 10% of that for your vent opening. Just as your inner arch height is 63% of the dome height (the so called golden mean). As far as planning ahead, think of the inner arch. I think the whole dome is built around it.

Good Luck

Tom

[Faith In Virginia]

That does not sound right to me. by your calculation that would be 250 square inches of the opening (if rectangle and not arched) 10% is 25 sq inches of vent so that is like a 5"x 5" opening? I'm no expert but that sounds small to me.

[fxpose]

Originally Posted by lhuhn

Second, if I opt for the concrete vent construction do you need a special concrete mix or just basic concrete mix?

Yes, you need to use refractory cement mix as the vent gets extremely hot.

I designed and molded my vent using Rutland castable refractory cement.

[dmun]

Yes, you shouldn't use portland concrete for your vent transition. Way too hot.

[Tscarborough]

The 10% ROT is for fireplace openings/flue size, but the same principle applies. It is always better to err on the side of larger, though.