The short answer
Adding insulation from R-19 to R-49 over a 1,500 sq ft attic saves about $93.98 a year on heating with a 95% gas furnace at U.S. average prices and winter, or $321.06 with electric baseboard heat. An uninsulated attic (about R-2) brought to R-49 saves $1,398.67 a year on gas; a $1,500 job pays back in 1.1 years.
Recommended attic R-values
ENERGY STAR's recommended attic insulation when retrofitting an existing home, by climate zone (from the 2021 IECC):
| Climate zone | Uninsulated attic | Already 3 to 4 in: add |
|---|---|---|
| Zone 1 | R-30 | R-25 |
| Zones 2 and 3 | R-49 | R-38 |
| Zones 4 to 8 | R-60 | R-49 |
How it works
The formula
saved = loss at today's R − loss at the new R
dollars = saved ÷ heating efficiency × fuel price
Assumptions
- The heat-loss formula is the one Penn State's energy course uses for roofs and payback. Degree days are NOAA's 1991-2020 normals for your ZIP's nearest station, or your state's average.
- R-values are for the whole ceiling. With no insulation, drywall and the still air on each side give roughly R-2. Settled cellulose adds about R-3.6 an inch (GreenFiber's chart: R-38 at 10.4 in); check the bag or batt label for yours.
- Recommended levels are ENERGY STAR's.
- Heat pumps use the same seasonal efficiency as our heat pump vs furnace calculator. Summer cooling savings and air sealing aren't counted.
Worked example: R-19 to R-49
- Before: 1,500 × 5,200 × 24 ÷ 19 = 9.9 million Btu
- After: ÷ 49 = 3.8 million Btu
- Saved 6 million Btu × $15.58 per million (95% gas) = $93.98 a year
Ways to cut the cost
- Seal first: close gaps around lights, pipes and the attic hatch before adding insulation.
- The first inches pay most: a bare attic gains far more than one that's already at R-30.
- Keep soffit vents open with baffles when you blow in more.
Questions people ask
How much does attic insulation save?
Going from R-19 to R-49 over a 1,500 sq ft attic saves about 6 million Btu of heat a year at the U.S. average winter (5,200 degree days): $93.98 with a 95% gas furnace at U.S. average prices, $321.06 with electric baseboard heat. An attic with no insulation (about R-2, drywall and still air) saves far more: $1,398.67 a year on gas.
What R-value should my attic have?
For an uninsulated attic, ENERGY STAR recommends R-30 in zone 1, R-49 in zones 2 and 3, R-60 in zones 4 to 8. With 3 to 4 inches already there, it suggests adding R-25 in zone 1, R-38 in zones 2 and 3, R-49 in zones 4 to 8. Its levels follow the 2021 IECC.
Is adding insulation worth it?
Usually, if the attic has less than R-19 or so. Each added inch saves less than the one before, because heat loss falls as 1 ÷ R: going from R-2 to R-19 saves much more than from R-30 to R-49. Type the job cost to see the payback.
Does it help with air conditioning too?
Yes, but this calculator counts winter heating only. In hot climates the summer savings can be as large; air sealing the attic floor before adding insulation helps both.