The Espar Airtronics D2 heater, providing 7,500 btu, allows users to stay warm and save fuel while in the bunk heater. Running over 20 hours on a gallon of fuel, the D2 pays for itself in as little as 40 nights, according to the company. Thermostatically controlled with four automatic heat levels, the Espar D2 works well to stay comfortable during cold weather nights. Available in 12V and 24V.