With all the different calculators I have come across most seem like garbage. Can anyone link to a reliable calculator for energy saving by adding insulation. Preferably one that takes into account wall, floor and ceiling insulation, energy rates, window types (ie double pane), square footage of house, preferred temperature, duct insulation and efficiency of heating/cooling equipment. Right now my attic equals about R17. I found I can increase to R29 for about $300 by adding loose fill cellulose myself or R40 for $500 30% either can be off set as a tax credit so I'm trying to see how much I should go to before the increase in insulation cost is not worth the energy savings. Given that my framing is spaced 16 in. off center and that I have 1/2 in drywall my ceiling should easily handle the additional load as even going to R49 will only bring me to 1.75 lbs per sq ft including current loose fill fiberglass while it can handle 2.2 lbs per sq ft before sagging. So weight is not an issue.