Thanks. I forgot I also installed energy efficient windows so that is probably why it went up to $410 (not $491).
In that case you may be able to get the credit up to the maximum of $500. If your system is an electric heat pump, you max out at $300, but if it's a gas furnace plus A/C, and both parts meet the required efficiency standard, then you could split the cost and enter the single upgrade in both the furnace and A/C categories, that should get you close to $450, then the windows will put you to the $500 maximum. Unless your credit is limited because you took it previously (the $500 is a lifetime maximum per taxpayer, not per home).