A linked heating and cooling system is when the heating and/or cooling coil is integrated with the ventilation system, employing air as the distribution fluid (air handler, fan coil, packaged unit, furnace, etc.).

An unlinked heating and cooling system is when  the ventilation system (if present) is separate from the heating coil, and heat is provided without requiring fan-powered air delivery. Unlinked heating technologies include radiators, baseboard electric, or infrared heaters.

Currently, FEDS assumes that all cooling is linked, with the exception of evaporative coolers, which are assigned a separate, special ventilation scenario. For more detailed information see Section 4.4.2 of the FEDS User's Guide.