We incorporated advanced engineering, for strength and ease of assembly, with an attractive oval design. Heated Kitty Sill operates on only 6 watts. Its dual thermostat heating unit is buried deep within super soft orthopedic foam and is removable for year round comfort. The heater is set to keep the surface 12 to 15 degrees above ambient air temperature, and to warm to a cat-pleasing 102 degrees with the Kitty on it. No tools are necessary for installation when using the provided Velcro fasteners. We also include screws for a more permanent attachment. Either way, Kitty Sill is the sturdiest window perch on the market. UL and CUL listed.