Sumter County, SC Insulation Payback
Attic insulation payback for Sumter County, SC
DOE classifies Sumter County as climate zone 3, mixed-humid — heating load in winter and cooling load in summer, both worth taking seriously here. Its recommended attic R-value for bare joists is R-49. For an attic around 1,000 square feet, closing the gap from R-2 to R-49 costs around $2,820 and saves an estimated $1,035 a year — payback in roughly 2.7 years. Hard to find a home improvement with a faster payback than this.
Heating vs. cooling in Sumter County
Of that, about $748/year comes from reduced heating and $286/year from reduced cooling load through the ceiling. Sumter County beats 19% of the counties in this 3,162-county dataset on estimated insulation savings. Among the 690 counties DOE places in zone 3, Sumter County ranks 400th. Against South Carolina's own average of $1,016/year, Sumter County runs 2% above that.
Sumter County's actual weather, not a national average
The heating and cooling degree days behind this estimate — 2,821 HDD and 1,796 CDD (base 65°F, 1991-2020 normals) — come from SUMTER, SC US, the nearest NOAA station with published normals, 2 miles from Sumter County's center. That combined heating-and-cooling load ranks Sumter County 2719th nationally by total degree days — the 14th percentile. DOE also classifies Sumter County as moisture regime A (humid) - ask a local contractor whether that changes the vapor-barrier approach for this job.
Already have some insulation?
If Sumter County's attic already has 3-4 inches of old insulation (about R-11) rather than bare joists, the recommended target drops to R-38. That smaller top-up costs around $1,620 and saves an estimated $139/year — payback about 11.6 years. It is close - the payback only just fits a reasonable timeframe.
Getting it done in Sumter County
Get more than one quote before committing. Attic access and any needed air sealing move the price around, and most contractors won't take a job below roughly $600 regardless of size - worth asking upfront given Sumter County's estimated $1,035/year on the line.
More on how this was built
Nothing here is a guess: the methodology guide names the DOE climate map and NOAA station data behind every number on this page. See the DIY vs. contractor guide for whether a job this size is realistic to do yourself.