I was looking through product info this morning and noticed (it got no press that I saw) that the DOE, after a protracted battle with the HVAC industry, started enforcing its new 13 SEER (up from 10 SEER) energy efficiency standard for all new a/c units sold in the US. The primary difference between a 10 and 13 SEER unit needed to achieve the higher energy efficiency was simply increasing the coil size, improving heat transfer on both ends of the cycle. This does, however, result in larger equiment and more refrigerant, for higher costs, but the difference isn't that great compared to an ~23% reduction in energy usage for the same capacity. I'm a big fan of this and I think the DOE should immediately start planning for the next increase. 13 SEER units have, of course, been available for years (just under the guise of "high efficiency") and utilizing things like multi-speed compressors and condenser fans, virtually every major manufacturer offers units above 15 SEER. Trane has an "up to" 19.5 SEER unit and Carrier has an "up to" 21 SEER unit. Unfortunately, energy savings payback calculations are not easy because pricing isn't easy to obtain (you get it through your contractor), but I'll try to ballpark it (lots of guesses): 10 SEER (80% furnace) unit: $4,000 installed $800/ yr A/C costs (4 month season on a decent-sized house) 13 SEER (94% furnace) unit: $5,000 installed $616 / yr A/C costs So that would be a $184 per year savings, or a 6 year payback. Higher efficiency (than 13 SEER) units probably cost significantly more, but part of that is due to added features that add comfort, such as better controls, variable fan speeds, and quieter operation. Few people make decisions that over 6 years will save them money (see recent conversations on compact fluorescent bulbs), so this is one area that the government (and gung-ho engineers like me ) needs to give people a little kick to convince (force) them to do it. http://www.residential.carrier.com/knowledge/efficiency/govstandards.shtml" both have good information on their websites about this change.