Features and Benefits:�Double skinned combustion chamber for thermo-acoustic insulation and safe low surface temperature, Stainless steel heat exchanger, Preheated oil filter, Electronic flame control system, Safety overheat thermostat and pressure switchThe HS3500DF is just the right size for the job if the job is huge. Delivering a whopping 360,000 BTUs at 1800 CFM this heater can handle almost any jobsite. Included on this unit is an external hook-up for a remote thermostat, onboard diagnostics and all of the other safety bells and whistles you have come to expect from the product at Heatstar. With a gigantic 27 gallon tank you can run this unit for 9 hours on a single fill up. This HS3500DF is always on the job.