The Contractor on a project currently under construction has asked a question that I have not yet encountered on the previous (4) LEED-certified projects that I've worked on: He has asked if a "direct" heater can be used if it is outside of the building envelop. We both understand that temporary heaters have to be stationed 'outside' and that 100% O.A. has to be used, but the description of how a "direct" heater works sounds akin to running a hose from a car exhaust to the building. I cannot find any language in SMACNA Ch3 or the LEED Ref. manual that discusses this, as do both for what MERV filtration media must be used if permanently-installed HVAC equipment is used.