One of the main sources of carbon emissions generated by hotel operations are in-room air conditioners used for both heating and cooling. This study tests several message-based approaches that leverage promising latent theoretical constructs (e.g., social norms, compassion, perceived anthropomorphism, and humor) to encourage hotel guests to set the air conditioner in a specific range, which reduces emissions without compromising guest experience in both winter and summer. Several messages are effective in triggering the targeted theoretical constructs, with eight (4 in winter and 4 in summer) messages also translating into sustainable air conditioner use. This study demonstrates how simple and cheap messages can influence behavior and substantially reduce hotel-generated carbon emissions; a change in 1 degree can reduce emission by up to 6%.