Rebates on an insulation project! Want to participate in the NJ Home Performance with Energy Star program? Have a newer or midlife HVAC system? We want to air seal and insulate your home! 
Let us break it down in easy terms: An 80% furnace running in peak season (cold weather) with no air sealing and insulation under R-49. You home will leak conditioned air, and the insulation will not be thick enough to hold it in. Think about what your efficiency is after losing your conditioned air.
Same scenario with a High Efficiency furnace a 96%, the furnace may be cheaper to run at the same length of time, but it is still running and still losing heat. Why by a larger furnace (cost you more out of pocket), and run that furnace non-stop?
By air sealing and insulating first, you reduce the size of the furnace, and your home becomes much more comfortable. Stop going hot and cold throughout your night… a nice even heat is much better. The same scenario also works in the summer months!