An air handling unit (AHU) for a heating, ventilation, air conditioning, and refrigeration (HVACR) system includes a housing and a combustion heater disposed within the housing. The housing includes a combustion section with a first channel and a second channel. The combustion heater includes heat exchanger tubes and a tube support that supports heat exchanger tubes within the combustion section. The tube support slidably disposed in the first channel and the second channel. The combustion heater configured to be slidably removable from the AHU. An AHU for an HVACR system includes a housing with a fan section and a fan assembly disposed within the housing. The fan assembly including a pair of grooves slidably disposed on a pair of rails of the housing. The fan assembly configured to be both slidably removable from the AHU and liftably removable from the AHU.