Direct Venting System : A venting system that is constructed and installed so that air for combustion and draft control is taken from interior building spaces and all combustion products are discharged to the outside atmosphere
NFPA 31 Standard for the Installation of Oil-Burning Equipment, 2001 ed. https://www.nfpa.org/Assets/files/AboutTheCodes/31 /LPI-AAA_ROPagenda_06-09.pdf, (Std: Install of Oil-Burn Equip - Amer) {195 NFC}