Hydro Flame's 8500 & 8900 Excalibur Series Furnaces will appeal to manufactureers, servicemen and owners alike. The compact size & especially the low profile will provide greater flexibility in termining furnace location. this benefit will result in supplying valuable storage space. The Excalibur was designed to be installed and serviced from the exterior of the RV. This innovation allows for product servicing without furnace removal, and also eliminates the need for the internal access door. the Excalibur furnaces incorporate a unique adjustable outside vent draft tube design, eliminating the need to purchase a separate vent. all models are direct spark ignition.DOORS & THERMOSTAT MUST BE ORDERED SEPARATELY!!!Excalibur 8500 IV series:37639 - 8516-IVDCLP6 w/o thermostat - 16K BTU Furnace37638 - 8520-IVDCLP6 w/o thermostat - 20K BTU Furnace37637 - 8525-IVDCLP6 w/o thermostat - 25K BTU Furnace37636 - 8531-IVDCLP6 w/o thermostat - 31K BTU Furnace37635 - 8535-IVDCLP6 w/o thermostat - 35K BTU Furnace(Cut out size required: 19 1/2"W x 7 1/2"H x 18"D)Excalibur 8900 III series:36917 - 8940-III DC w/o thermostat - 40K BTU FurnaceNOTE: for new installation of EXcalibur 8900 series, a Recess Pan (bezel) is required. Available by special order.