Yes, that's right, it has to be primary residence. That was true for the 2011 credit and still true for the 2012 and 2013 credits. If you take the credit for a boiler and you are renting half of your primary residence, then you only get to take half the credit too. Here is an updated link: http://www.energystar.gov/index.cfm?c=tax_credits.tx_index.