With an integrated fan that's thermostatically controlled, Espar air heaters circulate warm air throughout the vehicle, unlike most portable propane and electric-powered heaters that have a limited heat radius.
Espar systems run much quieter than those powered by diesel APUs or generators, creating a better environment for restful sleep.
The Espar Airtronic D2, for example, consumes about one gallon of fuel every 20 to 24 hours, compared to engine idling, which burns one gallon of fuel every one to two hours.
Espar heaters are integrated with the vehicle's primary fuel system. So, as long as there is fuel in the vehicle, you'll have continuous heat, unlike with portable propane heaters where you're having get up to replace empty tanks every few hours.