For high output heat why not consider these veratile bin heaters. Fireded by LP propane gas cylinders these provide an adjustable heat output from 15kW to an amazingly powerful maximum of 25kW (84,000btu).
These heaters are not pretty but solve heating solutions in warehouses, factories, construction sites, barns and other large spaces.
For ease of use these are fitted with a piezo ignition switch for easy start up. These units are extremley popular in the agriculural and construction industry because they require no other power source once connected to the gas cylinder.