US DOE proudly
Estimating the Payback Period of Additional Insulation
Suppose that you want to know how many years it will take to recover the cost of installing additional insulation in your attic. You are planning to increase the level of insulation from R-19 (6-inch fiberglass batts with moisture barrier on the warm side) to R-30 by adding R-11 (3.5-inch unfaced fiberglass batts). You have a gas furnace with an AFUE of 0.88. You also pay $0.87/therm for natural gas. Let's also suppose that you supply the following values for the variables in the formula.
C(i) = $0.18/square foot
C(e) = ($0.87/therm)÷(100,000 Btu/therm) = $0.0000087/Btu
E = 0.88
R(1) = 19
R(2) = 30
R(2) - R(1) = 11
HDD = 7000
By plugging the numbers into the formula, you obtain the years to payback:
Years to Payback = (C(i) × R(1) × R(2) × E) ÷ (C(e) × [R(2) - R(1)] × HDD × 24)
(Note to USDOE/ NREL: Your web page needs repair.)
Anyone will know about "diminishing returns" with piling on blankets.
Years to Payback = (0.18 × 19 × 30 × 0.88) ÷ ($0.0000087 × 11 × 7000 × 24)
90.288 ÷ 16.077 = 5.62 years
Same Example, Phillip Norman Attic Access
I pay $0.203 per sf for Johns Manville R11, after recent 10% increase for lack of demand where weatherization is NOT HAPPENING, and bid as times 2.5, installed total cost, or $0.509 per sf.
Natural gas costs more than $0.87 per therm. I pay about $1.20 per therm for natural gas heat, and know real cost with fracking permanent ruin of lands and water, and with war to fuel subsidized Hummers and corporate jets, is higher, maybe times ten. Real cost should always be used when rationalizing public policy. I use $2 per therm, a LOW number.
Annual cost of heat lost through insulation is:
$2.4 * 7000/4400 * (1/(Ri + 3)), per sf.
Annual savings R30 vs R19, are:
$3.82 * (1/22 - 1/33) = $0.058 per sf.
Simple payback with professional install is 0.509/ 0.058 = 8.8 years. Or, with self-install, divide by 2.5, for result 3.5 years.
Don’t stop at R30 though, despite slowing of payback with added insulation.
Add to R38:
Ci professional install adding unfaced R19, is $0.316 per sf * 2.5 = $.790 per sf.
Annual savings are $3.82 * (1/22- 1/41) per sf = $0.080 per sf.
Simple payback, professional install, is .79/ .08 = 9.8 years.
More-correct math does not change the picture. There is broad agreement we should have a lot more than R19 in our attic floors. Let's just do it. But DO NOT ADD MORE INSULATION before finding and closing attic floor pits, fixing enclosed fans and ducts, and replacing bad wiring in the process of conversion to LED lighting. What does US DOE have to say about any of that? Just bring out the blower door and wish all your troubles away, we understand. Send workers into an attic with a can of foam, and no contract to find and fix the greatest energy losses.
US Department of Energy knows nothing, and does nothing here. They must not be immune from criticism. Will they come clean, and rid us of phony HPwES ? In hard times, can we deprive them of funding to do careless work?
I think we should fully defund US Department of Energy, if it must remain the originator and maintainer of evil nuclear weapons. All within USDOE, and in state Departments Of Energy, are corrupted by this association, thus advocacy, of WMDs. This grousing is added 2/8/2014, where I have once again tested, to see that the stupid post by USDOE is immune from public comment. Know I have made calls directly to USDOE (some powerless answerer at Booz Allen Hamilton), and to NREL, to no effect.