A vent-free gas-heating appliance operates without a chimney, flue or vent, so you can install one just about anywhere. Key points: -They’re 99.9% efficient. -They have low operating costs. -They provide warmth during power outages and localized comfort to rooms that are hard to heat. -They are design certified and tested to meet the latest national safety standards. -Over 10 million homes in America use vent-free gas heating. Worldwide, usage exceeds 45 million homes. -Vent-free gas heating is the number one source of supplemental heat.