Multifamily Ventilation Requirements
Exhaust-only ventilation is no longer permitted as a whole-dwelling-unit strategy. New multifamily units must use supply-only or balanced ventilation — and in eight climate zones a balanced system must include an HRV or ERV.
The change: exhaust-only is out
For all new construction multifamily units, the whole-dwelling-unit ventilation strategy must be supply-only or balanced. Exhaust-only ventilation is not permitted for whole dwelling unit ventilation.
This is a real change in approach rather than a tightened number. An exhaust-only system depressurises the unit and pulls replacement air in through whatever gaps exist — which in an apartment building means from corridors, from shafts, and from neighbouring units. You get ventilation, but you do not control where the air came from.
In a detached house that is mostly a comfort question. In multifamily it is an air quality question, because the air arriving is somebody else's.
Supply-only or balanced
Supply-only pushes filtered outside air in, slightly pressurising the unit so leakage goes outward. Balanced supplies and exhausts roughly equal volumes, so the unit stays near neutral pressure and both air streams are through known paths.
Both share the property that matters here: the incoming air comes from a designed opening rather than from an unknown one.
Fan efficacy, in climate zones 4 through 10
For multifamily buildings up to three stories in climate zones 4 through 10, a balanced ventilation system without heat or energy recovery must have a fan efficacy of 0.4 W/CFM or less.
That is a demanding figure and it is a fan selection criterion, not something a control strategy can rescue. It exists because a balanced system runs two fans continuously — inefficient fans running all year is a large load accumulated quietly.
HRV or ERV, in the other eight zones
For balanced systems in climate zones 1, 2 and 11 through 16, an HRV or ERV must be installed.
Read the two zone lists together and the logic is visible. Zones 4 to 10 are the mild ones, where the temperature difference between incoming and outgoing air is small and recovering heat from it saves little — so the code asks for efficient fans instead. Zones 1, 2 and 11 to 16 are the cold and the hot extremes, where the air being exhausted is worth a great deal more than the air coming in, and recovery pays.
An HRV transfers heat; an ERV transfers heat and moisture. Both let a balanced system exchange air without discarding the energy already spent conditioning it.
What to settle in design
The climate zone, the number of habitable stories, and whether the ventilation strategy is supply-only or balanced. Those three answers determine whether a recovery unit is required and what fan efficacy the equipment has to meet — and a recovery ventilator needs space, ducting and service access that a simple exhaust fan never did.