Exhaust vent

[bunyip]

Hello everyone, I run propane burners here & have built a few different size furnaces over a period of time.Now, I know there are a number of variables with burners; example natural air, forced air, jet size & a whole gammit of other factors.With this in mind do any of the other members have a formula/rough guide to make a best guess for the size of the lid exhaust for different size furnaces? My mistake has been to make the hole too small on some & it's a pain to then make the opening bigger & have realised it's probably better to make the opening too big as at least that's easier to close off a bit. Cheers Trev.

[mite5255]

Hi Trev. When I built mine I used a very scientific formula ,I sat down with a beer and pondered the problem, still no answer so I sat there pondering and having a few more ales when it hit me, I had a piece of 90mm plastic pipe and though yep about that size and low and behold it worked,,, It was the beer that help solve the problem in case you hadn't fired it out

Mike

[Rasper]

You want a hole big enough to put pieces of metal through as you add them to your crucible during a melt. Too big is much better than too small. If it's too big and you lose too much heat, place a brick over part of the hole. If the brick melts after a few pours, get another brick.

Richard

[dallen]

I figure 4 inches is about right from all the thinking that I've done on the subject. 4 inches stops you from having to chop car wheels up into little tiny bits, and like Rasper said if its too large and your not heating the metal stick a brick over it, if it melts get a better brick, or make one from refractory.