40 and a lower portion 42 each of which is made up of interfitted sections 24 as illustrated in fig6 and 7 a channel 46 is provided through the box from a first end 48 to a second end 50 for transport of workpieces therethrough a plurality of susceptor rods 51 are disposed along the length of the thermal box between the first and second ends the rods are spaced from each other and quartz rods 53 are disposed between adjacent susceptor rods to maintain the spacing of the susceptor rods along the length of the chamber defined by channel 46 the susceptor rods and quartz rods are supported on shelf areas 32 provided along the respective sides of the chamber the quartz rods are transparent to microwave energy the susceptor rods are absorptive of microwave energy and are heated by the microwave energy and radiate heat to the workpieces transported through the chamber in general the microwave power is of a level to provide a penetration depth in the susceptor rods of about 50 the susceptor rods and spacer elements can be of any shape and size to produce the desired absorption and transmission of microwaves the rods collectively provide an intended thermal mass to be heated by the microwaves and to radiate in the chamber to heat workpieces in the chamber the susceptor rod sizes and the spacing between adjacent rods are determined to produce the intended temperature uniformity in the furnace chamber and.