How to Estimate Savings with Insulation in Southern Maine
One of the reasons people look to re-insulate their homes in Maine is because they know that month after month, year after year they are losing money. When we have good home insulation, we have more energy efficient homes. That is because the resistance value or R-Value of the homes is prevent heated air from traveling out of the house during the winter or into the house during the summer. But, how much difference does insulation really make?
There are several factors that come into play when determining how much money can be saved with spray foam insulation. This includes the age of the home, the size of the home, the current monthly heating and cooling costs, and the cost for new home insulation.
The following equation was prepared by the U.S. Department of Energy and it provides good guidelines for determining how long it will take insulation to pay for itself. The amount saved in heating or cooling costs over the years will end up paying for the insulation added to a house.
This equation works for uniformly insulated sections of the home. So, if different parts of the home have walls and insulation with different thickness and R-Values, it throws a cog into the mix and will complicate the calculations.
Here is the equation:
Years to Pay Back = (C(i) x R(1) x R(2) x E) = (C(e) x [R(2) – R(1)] x HDD x 24)
C(i) stands for the cost of insulation in terms of dollars per square foot. This would include the prep, labor, materials, and vapor barrier.
C(e) stands for the cost of energy in terms of dollars per BTU (or, British Thermal Unit).
The cost of energy is found by dividing the price you pay per kWh (kilowatt-hour) of electricity, gallon of oil or propane, or therm (one hundred feet of natural gas).
Look over your bills for the year. Some homeowners have a plan where they pay one cost monthly throughout the year. Otherwise, look back over twelve months of bills for your heating costs during the heating season and divide it by the total units used. Then, figure the following BTUs based on the type of heating used.
1 gallon of Fuel Oil #2 = 140,000 BTU
1 kWh Electricity = 3,413 BTU
1 gallon of Propane = 91,6000 BTU
1 ccf of Natural Gas = 103,000 BTU
1 Therm = 100,000 BTU
In the equation, E stands for the efficiency of the heating system. For fuel, gas, and propane heating systems, this is measure by the AFUE or Annual Fuel Utilization Efficiency. Propane furnaces should have an AFUE typically between 0.6 and 0.88. Natural gas furnaces will usually have an AFUE of 0.7 to 0.95, plug in “1” for “E” with baseboard electric heating systems. Heat pumps are measured by the COP or Coefficient of Performance. Conventional heat pumps usually have E = 2.1 to 2.5 while geothermal heat pumps have between 3.2 and 3.5 for E as a standard. It is important to note that older systems will be less efficient than these modern standards.
R(1) stands for the initial R-Value of the section. An insulation installer should be able to provide you with this value after performing a thorough inspection and before providing and finalized quote.
R(2) is the R-Value of the exterior walls after new insulation has been installed.
R(2) – R(1) shows us the additional thermal resistance rating when the new installation has been installed as compared to what it was before new installation was installed.
HDD stands for Heating degree days per year. The utility company you use to heat your home should be able to provide this number. You might also find it through your local weather station. Essentially, this is the average number of days temperatures dropped low enough that heaters would kick on (usually below 70 degrees or so).
24 is used to convert the heating degree days into heating hours. After all, there are 24 hours in a day, right?
Examples of Payback time for insulation.
C(i) = $0.30 per square foot
C(e) = $0.90 per therm / 1k BTU = $0.000009 per BTU
E = 0.88
R(1) = 19
R(2) = 30
R(2) – R(1) = 11
Looking back at the formula:
Years to Payback = (C(i) × R(1) × R(2) × E) ÷ (C(e) × [R(2) – R(1)] × HDD × 24)
So, we end up with
(0.25 x 19 x 30 x 0.88) / ($0.000009 x 11 x 7000 x 24)
125.4 / 16.632 = 7.54 years
It can be a complex process and your Maine insulation installer should be able to help you walk through and figure these out. It is possible your exact payback time will be more or less than this calculation depending on other factors, but this should give you a general idea of when you can expect new insulation to pay off. Imagine, even in this example, the new insulation costs upfront, but is saving money year after year on the heating and cooling. Also, less stress is being put on the HVAC system, so maintenance for that is lessened and its lifespan is thus extended.
For additional information on how to make your home more energy efficient with new insulation, please give us a call: