Two years ago I upgraded my attic insulation to R38 --- recently I
was
looking at possibly increasing my attic insulation up to R76 - and I
wanted to know what was the payback (return on investment) - after
much surfing I found the formula below. HTH
The following webpage coves estimating
the payback for adding Insulation to the Attic
http://apps1.eere.energy.gov/consumer/your_home/insulation_airsealing/index=
.cfm/mytopic=11360
(incase the above webpage dissappears ....)
the equation is as follows:
Years to Payback = (C(i) × R(1) × R(2) × E) ÷ (C(e) × =
[R(2) -
R(1)] × HDD × 24)
To calculate the payback, you must supply the following information:
C(i) = Cost of insulation in $/square feet.
Collect insulation cost information;
include labor, equipment, and vapor barrier if needed.
C(e) = Cost of energy, expressed in $/Btu.
* To calculate the cost of energy, divide the actual price you pay
per gallon of oil, kilowatt-hour (kWh) of electricity, gallon of
propane, or therm (or per one hundred cubic feet [ccf]) of natural gas
by the Btu content per unit of fuel.
* To figure the price you pay per unit, take the total amount of your
bills (for oil, electricity, propane, or natural gas) during the
heating season, and divide it by the total number of gallons, kWh, or
therms you consumed during those months. Use the following values for
fuel Btu content:
Fuel Oil = 140,000 Btu/gallon
Electricity = 3,413 Btu/kWh
Propane = 91,600 Btu/gallon
Natural Gas = 103,000 Btu/ccf
or 100,000 Btu/therm
E = Efficiency of the heating system. For gas, propane, and fuel oil
systems this is the Annual Fuel Utilization Efficiency or AFUE.
Typical AFUE values are 0.6 to 0.88 for oil or propane furnaces, and
0.7 to 0.95 for natural gas furnaces. Older systems are usually less
efficient. Use E = 1.00 for baseboard electric systems. For heat
pumps, use the Coefficient of Performance or COP for E; where E = 2.1
to 2.5 for conventional heat pumps, and E = 3.2 to 3.5 for geothermal
heat pumps.
( an energy star non-geothermal HVAC is typically going to have an
E=2.5 )
R(1) = Initial R-value of section
R(2) = Final R-value of section
R(2) - R(1) = R-value of additional insulation being considered
HDD = Heating degree days/year. This information can usually be
obtained from your local weather station, utility, or oil dealer.
( e.g. for HDD for MD-DC-VA see [1])
24 = Multiplier used to convert heating degree days to heating hours
(24 hours/day).
Example:
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)
Years to Payback = (0.18 × 19 × 30 × 0.88) ÷ ($0.0000087 =
× 11 ×
7000 × 24)
90.288 ÷ 16.077 = 5.62 years
[1]HDD
district of columbia
http://www.efficientwindows.org/codes/DC-IECC.pdf
maryland
http://www.efficientwindows.org/codes/MD-IECC.pdf
Virginia
http://www.efficientwindows.org/codes/va-IECC.pdf
> Two years ago I upgraded my attic insulation to R38 --- recently I
> was
> looking at possibly increasing my attic insulation up to R76 - and I
> wanted to know what was the payback (return on investment) - after
> much surfing I found the formula below. HTH
> The following webpage coves estimating
> the payback for adding Insulation to the Attic
The infrared thermometer and snow melt pattern show that most of my
remaining attic heat loss is around the edges where I couldn't stuff
in more insulation due to restricted space and protruding roofing
nails. More insulation in the middle wouldn't help much if that isn't
where the larger losses occur.
> > Two years ago I upgraded my attic insulation to R38 --- recently I
> > was
> > looking at possibly increasing my attic insulation up to R76 - and I
> > wanted to know what was the payback (return on investment) - after
> > much surfing I found the formula below. HTH
> > The following webpage coves estimating
> > the payback for adding Insulation to the Attic
> The infrared thermometer and snow melt pattern show that most of my
> remaining attic heat loss is around the edges where I couldn't stuff
> in more insulation due to restricted space and protruding roofing
> nails. More insulation in the middle wouldn't help much if that isn't
> where the larger losses occur.
Sound like a great idea! The farmer's almanac predicts
lotsa of snow this winter for the Mid-Atlanic area so maybe
I'll get a chance to do just that....
> Two years ago I upgraded my attic insulation to R38 --- recently I
> was
> looking at possibly increasing my attic insulation up to R76 - and I
> wanted to know what was the payback (return on investment) - after
> much surfing I found the formula below. HTH
> The following webpage coves estimating
> the payback for adding Insulation to the Attic
> http://apps1.eere.energy.gov/consumer/your_home/insulation_airsealing ...
> (incase the above webpage dissappears ....)
> the equation is as follows:
> Years to Payback = (C(i) × R(1) × R(2) × E) ÷ (C(e) × [R(2) -
> R(1)] × HDD × 24)
> To calculate the payback, you must supply the following information:
> C(i) = Cost of insulation in $/square feet.
> Collect insulation cost information;
> include labor, equipment, and vapor barrier if needed.
> C(e) = Cost of energy, expressed in $/Btu.
> * To calculate the cost of energy, divide the actual price you pay
> per gallon of oil, kilowatt-hour (kWh) of electricity, gallon of
> propane, or therm (or per one hundred cubic feet [ccf]) of natural gas
> by the Btu content per unit of fuel.
> * To figure the price you pay per unit, take the total amount of your
> bills (for oil, electricity, propane, or natural gas) during the
> heating season, and divide it by the total number of gallons, kWh, or
> therms you consumed during those months. Use the following values for
> fuel Btu content:
> Fuel Oil = 140,000 Btu/gallon
> Electricity = 3,413 Btu/kWh
> Propane = 91,600 Btu/gallon
> Natural Gas = 103,000 Btu/ccf
> or 100,000 Btu/therm
> E = Efficiency of the heating system. For gas, propane, and fuel oil
> systems this is the Annual Fuel Utilization Efficiency or AFUE.
> Typical AFUE values are 0.6 to 0.88 for oil or propane furnaces, and
> 0.7 to 0.95 for natural gas furnaces. Older systems are usually less
> efficient. Use E = 1.00 for baseboard electric systems. For heat
> pumps, use the Coefficient of Performance or COP for E; where E = 2.1
> to 2.5 for conventional heat pumps, and E = 3.2 to 3.5 for geothermal
> heat pumps.
> ( an energy star non-geothermal HVAC is typically going to have an
> E=2.5 )
> R(1) = Initial R-value of section
> R(2) = Final R-value of section
> R(2) - R(1) = R-value of additional insulation being considered
> HDD = Heating degree days/year. This information can usually be
> obtained from your local weather station, utility, or oil dealer.
> ( e.g. for HDD for MD-DC-VA see [1])
> 24 = Multiplier used to convert heating degree days to heating hours
> (24 hours/day).
> Example:
> 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)
> Years to Payback = (0.18 × 19 × 30 × 0.88) ÷ ($0.0000087 × 11 ×
> 7000 × 24)
> 90.288 ÷ 16.077 = 5.62 years
> [1]HDD
> district of columbiahttp://www.efficientwindows.org/codes/DC-IECC.pdf
> marylandhttp://www.efficientwindows.org/codes/MD-IECC.pdf
> Virginiahttp://www.efficientwindows.org/codes/va-IECC.pdf
Research how Fiberglass batts loose R value as temps drop. Depending
on where you live and winter lows you can loose 20-30% R value as the
attic gets colder. Also settling. I put in R 100-110 fiberglass batts
and it settled to R 70. Best is Foam. What is your Zone. Settling and
R value loss at -f temps increase payback.
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> was
> looking at possibly increasing my attic insulation up to R76 - and I
> wanted to know what was the payback (return on investment) - after
> much surfing I found the formula below. HTH
> The following webpage coves estimating
> the payback for adding Insulation to the Attic