That’s right as part of fiscal cliff legislation, signed into law by President Obama on January 2, the 2011 energy tax credits are back for 2013 and are retroactive for qualifying equipment installed in 2012. So if you had a high efficiency furnace, air conditioner, heat pump, or water heater installed in 2012, you could qualify for up to a 300$ tax credit. If your thinking of upgrading to higher efficiency equipment, this year could be last time to take advantage of these extra credits.
So what qualifies? Gas furnaces of 95% AFUE qualify for 150$ credit. If it has a variable speed motor it gets you an extra 50$ on top of that. Heat pumps of 15 or more SEER and air conditioners of 16 or more SEER can qualify for a 300$ tax credit.
some more info can be found here.
http://www.hvacdist.com/current-tax.asp