How big aught the vent in a metal melting furnace be?

[S. Heslop]

Here's where i'm at right now.

I read a thing online that said to give it 7x the cross sectional area of the burner tube, which worked out to about 60mm diameter with an inch wide burner. I've made a stack of MDF discs as the inner form, but I'm sort of feeling it looks a little bit small.



I suppose itd make more sense to over-shoot the ideal size since you can cover it partially with a fire brick, but i'd rather not make it too big.

[doubleboost]

Hi
Mine vents through a 80 mm pipe (side vent) as the furnace is inside
The hole in the top is 100 mm closed with a fire brick
John

4-CXw

[tom osselton]

Mine has a 4" vent hole too.

[S. Heslop]

I guess 100mm is the way to go then. Thanks for the replies.