Humidity Control Of Mushroom Houses

I live in an area where almost everyone has mushroom houses including my MIL. To control humity here and/or to raise the humity level, and to sterilize things in mushroom houses my MIL and all of my neighbors burn used truck tires to fire up there steaming producing machine - a large brown, rusty, piece of junk with wheels that can send a cloud of black smoke high in the sky. Approximately everyother day for about 6 hours this black cloud is going up.

Since I know nothing about the subject of mushroom houses I thought I would seek assistance here.

I want to know all other methods of producing steam for mushroom houses. Information on companies that sell equipment, etc. Goggle has nothing that I could find. What ever you can provide will be fine.

Thank you