Whether you’re talking about central air, window air-conditioning units, or a minisplit system, there are two standards that measure cooling efficiency. The seasonal energy efficiency ratio (SEER) indicates the relative amount of energy needed to provide a specific cooling output. The energy efficiency ratio (EER) is defined as “the steady-state rate of heat energy removal in Btu (e.g., cooling capacity) by the equipment, divided by the steady-state rate of energy input to the equipment in watts.” The higher the ratio, the less the unit will cost to operate.
Bob Lange, owner of Guardian Heating and Cooling in Chicago, believes the EER ratings are a better indicator of cooling efficiency. “The SEER number is the best-case scenario, tested at low humidity,” he says.
If you attempt to compare SEER and EER, the Energy Star program suggests that an SEER of 14.5 for a central air system is roughly equivalent to an EER of 12 for a minisplit system.
The installed cost of a minisplit is more than the cost of a window unit (or units) but lower than central air (considering ductwork). Lange, whose company installs both central air conditioning and minisplit systems, has seen nothing but positive responses from his minisplit customers. “Usually I get very few calls from customers saying how satisfied they are with their [central] air conditioning, but just about every person who has a minisplit installed calls to say how much they enjoy it.”