Intertherm Roof Jacks Flue Assy 21in 35" No Slant. Check manufacturer recommendations for other models to ensure compatibility. Roof Jack Vents are used to provide furnaces with fresh air for combustion and vent out flue gasses. This Flue Assembly features a 21" to 35" extension when measured specifically for the roof and a 0/12 slant (pitch). Features of Intertherm 903659 Roof Jacks Flue Assy 21in 35" No Slant Compatible with M1 Series Hot Surface Ignition Furnaces M1 Series Gas Gun Furnaces and M5 Series Oil Gun Furnaces from Intertherm Check manufacturer recommendations for other models to ensure compatibility Used to provide furnaces with fresh air for combustion and vent out flue gasses 21" to 35" extension when measured specifically for the roof 0/12 slant (pitch). Package Contents: Intertherm 903659 Roof Jacks Flue Assy 21in 35" No Slant Intertherm 903659: Roof Jacks Flue Assy 21in 35" No Slant