Insulation Savings & Payback

Insulation savings do not follow the difference between two R-values. They follow the difference between two reciprocals, and that single fact changes most insulation decisions.

Heat loss through an assembly is proportional to 1/R. Going from R-0 to R-13 removes about three quarters of it. Going from R-38 to R-49 removes about six percent more. Same eleven points of R, wildly different value.

This is why "more R is always better" is bad advice, and why the answer to "should I add insulation" is almost always yes for an uninsulated attic and often no for one that already has R-38.

Three things decide the answer, and most advice names none of them

Climate. The same upgrade that saves $320 a year in Chicago saves about $76 in Houston. Advice written for one climate is simply wrong in another, and almost none of it says which climate it was written for.

Fuel. A heat pump delivers two and a half units of heat per unit of electricity. That makes the heat you are keeping in cheap, which is exactly why insulation pays back more slowly on a heat pump than on propane. Counter-intuitive, and it matters.

Where you are starting from. R-11 to R-38 is a completely different proposition from R-30 to R-38, even though both end in the same place.

What a good payback looks like

Under five years is genuinely good — very little you can buy for a house returns like that, and insulation has no moving parts and does not wear out. Five to twelve is reasonable if you are staying put. Beyond about fifteen, the heat you are losing is not worth enough to justify the work, and the money belongs in air sealing instead.

Air sealing first, and it is not close

Insulation slows heat moving by conduction. It does nothing about air moving bodily through gaps around can lights, top plates, ducts and the attic hatch. Blowing insulation over unsealed penetrations buries the problem somewhere you can no longer reach, and the return per dollar on sealing them is several times higher than the return on the last R-10.