How many watts a portable air conditioner uses varies. The models listed here use a minimum of 950 watts and increase from there. Though portable ACs are not intrinsically energy-efficient, your electric bill will depend on how often you use it/keep it turned on and what mode you have it on (e.g., full blast vs. sleep mode). If you are strategic, you can help cut your electric bill by using a portable AC. For example, instead of installing window units in every room, you simply move your unit around the house, saving you money. (Venting the hoses into the windows every time you move it could get tiresome, though.) Suppose you already have an AC and want a portable model as a supplement. In that case, you can save money that way too: Keep the thermostat higher than you typically would and use the portable only in the rooms you use, ignoring the empty ones.