De acordo com a NFPA 31, você precisará de duas aberturas. Um perto do topo e outro perto do fundo. Cada um dos quais deve ser de 1 pol² por 1000 Btu / h da taxa de entrada de todos os equipamentos no espaço confinado.
NFPA 31 Standard for Installation of Oil Burning Equipment.
Chapter 5 Air for Combustion and Ventilation.
5.4 Appliances Located in Confined Spaces.
5.4.1 All Air Taken from Inside the Building.
5.4.1.1 The confined space shall be provided with two permanent openings as shown in figure 5.4.1.1, one near the top of the space and one near the bottom.
5.4.1.2 Each opening shall have a free area of not less than 1 in.² per 1000 Btu/h (140 in.² per gal/h) (22 cm²/kw), based on the total input rating of all appliances in the space.