No, you cannot use the Portable Air Conditioner without attaching the exhaust hose. The compressor of air conditioner generates heat during the cooling process. Hot air must be vented outdoors through the exhaust hose to keep a cool indoor environment. If the exhaust air remains inside, it will counteract the cooling effect and may even make the room warmer. Either place the hose out the window for a quick set-up, or use the window kit to enhance cooling efficiency by preventing indoor and outdoor air exchange.