WEB FilterFresh whole home air freshener attaches to any furnace or air conditioner filter. The secret to a pleasant smelling house! As the central furnace/AC system runs a fresh scent is flows through the home. Great for parties, open houses, holidays and to help reduce lingering household odors like smoke, kitchen, bathroom and pet odors. Safer than candles and FilterFresh lasts longer than aerosol sprays. Scents last for days depending on the size of your home and how much the system is running.