A field-ready oven has reinforced telescoped side walls that extend and hold a base, shelf, tray support and cover spaced apart. A low air intake and a semipermeable membrane deliver air and vapor fuel to catalyst pads on the shelf. Radiant heat from exothermic reaction is diffused over a bottom of a tray. Hot gas circulates around the diffuser and tray with a chimney effect before exhausting. A lid on the cover lifts for access to the tray. A fuel container in the oven forces fuel through a capillary restriction to limit fuel flow. A spring in the container is released to start fuel flow.

A portable catalytic combustion heater, wherein fuel vapor (11) and air (10) are supplied to a catalyst (6) which promotes the flameless combustion of fuel and releases that. The fuel is supplied as a liquid, passes through a selectively permeable membrane (8) such that fuel vapor exits the membrane and is fed to the catalyst (6). Additional features include porous supports and means of enhancing and diminishing the catalytic rate of combustion and controlling the heat output.