in the heating apparatus thereby facilitating high speed operation and without unduly increasing the frictional resistance of the apparatus on the yarn application_number US 67054196 A description fig1 is a cross sectional view of a heating apparatus 1 which embodies the present invention and which includes a u shaped body having a u shaped channel 6 therein the channel 6 is of generally rectangular cross section so as to define parallel opposite side walls 5 and a bottom wall 15 the body is constructed such that the heating elements not shown arranged in the body deliver their heating energy above the bottom wall 15 as well as from the side walls 5 arranged in the groove are yarn guides 2 that are provided in generally flat plates 10 these yarn guides 2 are machined in the form of yarn guide slots in the plates 10 the slots extending substantially parallel to the side walls 5 and in a direction toward the groove bottom wall 15 depending on the yarn speed and existing heating energy as well as the yarn material the yarn guide slots may be arranged closer to the heating surfaces or be further removed therefrom however in accordance with the invention these yarn guide slots are always arranged in the region between the central plane which is defined centrally between the two side walls and one of the side walls 5 since a yarn not shown in fig1 which advances in the yarn guide slots undergoes a deflection on each yarn guide the deflection surfaces 16 are made round across the thickness of the plates 10 so as to exert the least possible influence on the yarn tension when the yarn enters into the yarn guide slot the.