Seasonal growers using long method compost often have no boiler. DMR publishes a chemical alternative applied at the last turning, after which the compost is heaped and covered with a polythene sheet for two days. Products and approvals change, so read the current label before using anything and never scale a published figure yourself.
DMR trial data on that treatment is useful context: 18.1 kg of mushrooms per 100 kg compost against 10.5 kg for a water sprayed control. Casing soil is a separate job, steamed at 60 to 65 degrees for 6 to 8 hours.