Abstract: A window accessory and sealing system offering an inexpensive, but efficient, alternative to replacing old windows with new windows. The window accessory and sealing system can be installed over a home's existing windows to effectively prevent heat loss and reduce utility bills. The product offers additional thermal insulation to effectively ensure that heat does not escape and cold air does not enter therein. The window accessory and sealing system comprising: a window; a convex window accessory with a one-way check valve. The window accessory is removably sealably-coupleable to the window to create an enclosed evacuatable inner volume. The one-way check valve is located on the convex window accessory and is used to create a vacuum seal between the window and the convex window accessory to minimize heat loss.