Or, very typically with amateur telescopes, heat is applied from a so called dew zapper. The dew zapper is a heating element whose purpose is to raise the temperature of the telescope slightly. Generally it is applied at the mirror or corrector plate since that surface seems the most subject to dewing. The amount of heat has to be held to the absolute minimum necessary to stop dewing, and no more, since there are other deleterious effects of heating and raising the temperature of the telescope above the ambient air temperature. Many amateurs find this equipment not only effective but necessary, especially when the telescope is used in the open or in a roll off building where it is exposed to the cold night sky.
Convection is the transfer of heat from the air to the surface or vice versa.
In order to increase the heat transfer from the air to the surface, the air must be moved. With good air motion, the telescope will move rapidly toward the ambient air temperature. This is good for several reasons. One is the reduction of heat waves just mentioned. Another is the reduction of the possibility of dew formation.