Fur 200, Flying Insect Screen, For Duro-Therm, Suburban, & Durotherm, Wasps, Mud Dauber Nests, Birds & Rodents Pose A Serious Threat To Your RV Water Heater, Furnace & Stove, They Can Enter Through Vents & Openings & Cause Serious Damage By Building Nests That Interfere With Air Flow, Easy To Install Screens Will Help Ensure That Your Vents Stay Free From Costly Invasion By Unwanted Pests.