The Collaborative International Dictionary of English v.0.48:

Unventilated \Unventilated\
   See ventilated.

WordNet (r) 3.0 (2006):

unventilated
    adj 1: not ventilated; "stuffy unventilated rooms" [ant:
           ventilated]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "unventilated":
   airless, blank, blind, blind-alley, breathless, breezeless, cecal,
   choked, choked off, close, closed, constricted, contracted, dead,
   dead-end, ill-ventilated, oppressive, shut, squeezed shut,
   stifling, strangulated, stuffy, suffocating, unopen, unopened,
   unvented, windless