To determine how well sealed (or airtight) a house is, close all doors and inlets in the house and switch on
one 122 cm (48 in)/127 cm (50 in) fan or two 91 cm (36 in) fans. The pressure within the house should not
measure less than 37.5 Pa (0.15 inches of water column). Pressure can be measured anywhere in the house
and should be consistent throughout the house.