The H2KM negative air machine is the perfect unit for contractors who want the very best in performance, reliability and quality. First stage polypad pre-filter: H2001, 40/cs. Second stage pleated pre-filter: H2002, 12/cs. Optional second stage carbon filter: VL2024, 6/ea. HEPA filter: H242406-99, 1/ea. Optional 12” replacement HEPA filter: H2010M, 1/ea.