When it comes to matching home appliances to your home's electrical capacity, one of the most confusing topics is voltage. Shopping for a window air conditioner can be even more confusing when different models of air conditioners with the same cooling capacity may be listed as 110-volt, 115-volt or 120-volt. Understanding the differences and how it applies to your specific outlet will help you prevent blowing a fuse or having to rest your breaker.
Standard Household Voltage
In most homes, the standard household voltage is 120 volts. The power company supplies two, 120-volt cables, or legs, of electrical current to your home. Where large appliances requiring 240-volt service appear in your home, an electrician has married the two cables for a specific outlet to provide the added voltage. Wires going to standard receptacles in your walls are 120 volts and are suitable for 110-volt or 115-volt air conditioners.
Window air conditioners may use anywhere from 110 volts to 240 volts of electricity to run efficiently. The easiest way to tell what sort of voltage the unit needs if the packaging is not available is to look at the unit's plug. A standard three-prong plug has a round, grounding prong above -- or below, depending on the wall receptacle's orientation -- two straight prongs, one of which is slightly larger than the other. The larger prong is "neutral" and the smaller prong is the "hot" connector. Units with these plugs use between 110 and 120 volts -- standard household electricity. In some cases, a 120-volt window air conditioning unit may have a round, three-prong plug of the same configuration.
Window units with standard, three-prong plugs may be used in regular household receptacles, regardless of whether the air conditioner requires 110-, 115- or 120-volt electricity. No special receptacle is required. However, if the unit has a round plug, you may consider changing the wall receptacle to match it.
The amount of power flowing to household receptacles can fluctuate by several volts due to the distance the power must travel, items plugged into the circuit between the power source and the air conditioner, and other, often arcane variables. The voltage actually supplied at a receptacle may be 120 volts, 115 volts, 110 volts, or anything in between. In most cases, the disparity is unnoticeable and normally does not affect the air conditioner's efficiency, even if the package calls for the unit to run on 120 volts and the receptacle's actual voltage is only 115 volts.
If you plug the air conditioner into an extension cord, the voltage may drop significantly, and this usually does affect the unit's efficiency. This is one reason extension cords are not recommended for use with heavy appliances like air conditioners.