My in-laws have an old potbelly stove sitting around. Some research indicates it was made around 1900. I smoked about 3 lbs of Pils malt on this stove on the 4th of July, and decided I’d see if it could crank out enough heat to brew a 5 gallon batch of beer.
The answer: almost.
It heated about 4.5 gallons of mash water fairly well, heating it 86.7 degrees in an hour. The slope leveled off a little as it reached strike temperature:
This performance of 390 degree-gallons per hour (when heating water starting at room temperature) is not too much worse than this same pot when I’m heating with a 1500W, 120V electric element – that setup yields about 480 degree-gallons per hour.
I mashed in an Igloo cooler and was able to heat sparge water to about 160F during the course of the mash.
Bringing 6.6 gallons of wort to a boil was a struggle, though, and the wort never attained a good boil. The best the stove could do with the pot’s lid off was about 205F. I covered the pot when stoking the fire – to keep out the ash that would blow around when the coals were disturbed – and would then remove the lid to find a vigorous (but temporary) boil as a result of the covering.
As a result, I had to boil for 2.5 hours to achieve my desired ~1.25 gallons of boil-off.
Better wood and more know-how might make a difference. We burned softwood, some of which was wet and/or rotten, and if we do this again we’ll try using higher-quality wood.
A bonus side experiment: this pot normally runs on electricity, which means it has a 1.25″ diameter hole in the side. I plugged that with an old heating element, not connected to anything. Would it melt? Yes, if unprotected. The plastic sagged a bit and may have dripped once before I put a thin piece of wood below it to shield it from the heat of the stovetop. But it remained watertight!