IF they kept the heat in, most the machines 'vent' a lot of it away to get rid of smoke etc, the venting is constant, smoke or not. Now if they kind of like your turkey oven, kept the heat in, then Id say its very possible because you don't have to keep replacing the heat lost during air changes. Granted there will be a bit lost thru the sides etc etc. Once it gets going, hits crack etc then start venting to get rid of smoke etc but I can see this being very doable.
Aaron