A wall plate for a wall thermostat blocks intrusion air from the thermostat. The wall plate has a wire passage aligned with the wall penetration through which the thermostat wires emerge. The wall plate member directs any intrusion air that flows out the penetration away from the cavity of said thermostat. An insulating layer, e.g., a closed-cell foam sheet, in the wall plate insulates the thermostat from direct thermal contact with the wall. The closed-cell material closes around the thermostat wires. Bosses or feet on the thermostat back plate create a standoff between the wall plate and the thermostat.