Two major decisions should guide your purchase of a room air conditioner. Buy a correctly sized unit. Buy an energy-efficient unit. If the room is very sunny, increase capacity by 10%. If the unit is for a kitchen, increase the capacity by 4,000 Btu per hour.
Purchase a heater with a guard around the heating element. A wire grill or other protection is essential to keep fingers or fabrics from touching the hot element. Portable electric heaters that heat by circulating oil or water, however, usually have lower surface temperatures and may not need guards.