smoke-cap

from The Century Dictionary.

• noun A device, such as a cowl or hood, on the top of a smoke-stack or chimney, designed to prevent gusts of wind from striking the unprotected opening from above and blowing the products of combustion downward or backward into the flue, carrying the smoke with them. Such caps may be simple deflectors, or they may be movable so as to turn the smoke outlet in the direction toward which the wind blows.