The presence of smoke in a conditioned space places an extra burden on the HVAC system. The smoky air can’t be recirculated and returned to the space after cooling it back down, as is the usual case with return air. The contaminated air must be exhausted. Then humid, untempered outside air must be cooled to make up the deficit. Usually, the outside air is at a higher temperature than the return air, so it is more difficult to cool. If the moisture content of the fresh air is higher—the usual circumstance—the expense of treating the air is even more.
Designation of a smoking area, preferably in a space isolated from adjacent conditioned zones by doors or corridors, ameliorates this circumstance. The volume of air affected is minimized, the quantity of air exhausted is reduced, and energy is saved in space-conditioning costs.
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Excerpt from Energy Conservation Projects.