How the insulation savings calculator works
The conduction math
Heat loss through a surface is Q = area × degree-days × 24 ÷ R (in BTU per season). The upgrade savings = the difference ÷ R-values × fuel cost per BTU. The calculator runs it end to end: a 1,200 sq ft ceiling going from R16 to R49 in a 4,500-HDD climate saves real money annually — typically $250–450 with gas heat, more with electric resistance.
Why degree-days drive everything
Heating degree days (HDD) measure how cold your climate actually was — base 65°F, each degree below adds a degree-day. Phoenix runs ~1,000 HDD; Minneapolis ~7,600. The same R16→R49 upgrade saves ~7× more in Minneapolis, which is why the same attic project is "no-brainer" up north and "reasonable" down south.
The honest stack
- Attic first: it is the cheapest R in the house and the biggest conduction surface.
- Air sealing rides along: the savings model assumes it — unsealed attic leaks cap real-world gains below the calculation.
- Ducts upstairs change everything: if your ducts run through the attic, duct sealing often beats insulation on payback — the losses compound.
Reading payback
Attic insulation is one of the rare home upgrades with a 2–5 year simple payback at typical costs — after which the savings are annuity income. Utilities frequently rebate the project (often 10–50%); check before buying bags, and ask about energy-audit discounts that stack.