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AC consumes 17% of the power used in the average home.

Plan Ahead

The typical central air conditioner lasts 12-15 years.  Don't wait until your unit fails or you may end up with whatever is left in your contractor's warehouse.  Ideally, weatherize and insulate beforehand.  And consider whether a zoned system would save carbon and costs.  Attend an LCAN B4UBuy workshop.

TIP:  Before replacing your AC, it's wise to hire a building performance contractor, such as a HERS rater, to assess whether your "building envelope" (foundation, walls and attic) needs weatherizing or more insulation and/or if your ducts need sealing.  If your AC unit went out and you're in a hurry, tell your HVAC contractor whether you plan to tighten up the envelope.  

Choose Your Technology

Before deciding on technology, consult an experienced HVAC contractor.  (If you don't already have a relationship with one you like, consider LCAN's tips for choosing contractors.)  You'll need to choose between various options:


  • Type:  Most Louisville homes have central AC; larger homes may have two zoned central units.  Modern electric heat-pumps can earn very attractive rebates and tax credits. Air-sourced heat pumps are best for most Louisville homes, though ground-source heat-pump (or "geothermal") systems are becoming more common.  Window units sometimes make sense.

  • Technology:  The least-cost and most-efficient option is often a geothermal system, which takes advantage of the always cool underground temperature, but usually entails drilling 6-inch diameter wells.  The next best option is an an air-source heat pump system.  Both ground-source and air-source also provide all or most of your heating! 

  • Efficiency:  Each AC model is rated on the basis of its Seasonal Energy Efficiency Ratio (SEER).  The higher the SEER, the better.  Choose a central unit with a SEER of at least 14.5; an Energy Star-rated model will use less power and save you money.  A "qualified" electric heat-pump system will earn most Louisville households a rebate and/or tax credit.  

An air-source heat pump looks like a regular outdoor central air conditioning unit, as shown in the photo, above.  A ground-source heat pump doesn't have outdoor equipment; everything is underground or where your furnace or boiler sat.   

A mini-split system cools or heats and cools spaces smaller than a whole house. The left unit mounts on an indoor wall; the right, on an exterior wall.

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TIPS:  Visit these web sites for more detailed information: offers guidance on replacing your AC and tips for operating it more efficiently and cost effectively.  For example, if your AC blows into leaky ducts within walls or ceilings, it will have to work harder to keep you comfortable; see the Duct Sealing page. ​ provides efficiency and cost information on numerous models currently on the market. helps you to find a model to

meet your needs and cut your carbon and costs.

If you don't subscribe to Consumer Reports, you could check out its ratings at the nearest Louisville Free Public Library.


Size Matters

If the system is over-sized, you'll be less comfortable and spend more to operate it.  If the system is sized for a leaky building envelope and you insulate or have ducts sealed later, it will be too big, less comfortable and more costly to operate.

TIP:  You can lower your cooling costs in numerous ways, from keeping curtains or blinds closed on sunny days and using a ceiling fan to insulating your attic better, choosing lighter-colored roofing and planting deciduous trees to provide shade during warm weather.  

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