ProRadiant™ Powerhead, 4-Wire, For Use With: Model 2874.5US Digital Thermostat, Model 2804/2879 Manifold, Model 2878.6 Thermostat Heat/Cool Non Programmable, Model 2878.7 Thermostat Heat/Cool Programmable, Thermostat Multistage Heat/Cool, Model 2878.8 Programmable, Model 2874.7US Zone Control, 24 VAC, Import