How does insulation R-value affect my energy savings?
R-value measures resistance to heat flow — the higher the R-value, the better the insulation. Savings are proportional to the reduction in heat loss, which follows the formula: heat loss ∝ 1/R. So upgrading from R-11 to R-38 dramatically cuts heat loss and therefore the fuel needed to maintain a comfortable temperature. See also our Energy Monitoring Dashboard Calculator.
What are Heating Degree Days and how do I find mine?
Heating Degree Days (HDD) measure how cold a location is over a year by summing the degrees each day's average temperature falls below 65°F. A higher HDD means more heating demand. You can find your local HDD value from NOAA's Climate Data Online or your utility company's website.
Why does furnace efficiency affect the savings estimate?
Not all fuel burned by your furnace converts into usable heat — some is lost through exhaust and inefficiencies. If your furnace is 80% efficient, only 80% of the fuel energy actually heats your home. A more efficient system means you need less fuel per BTU of heat delivered, so the fuel savings from better insulation are also slightly lower in dollar terms.
Is this calculator likely to overestimate or underestimate savings?
The calculator may slightly overestimate savings because it doesn't account for internal heat gains from people, appliances, and solar window gains. In colder climates with high HDD, this error is small. In milder climates (below ~3,000 HDD), actual savings could be noticeably less than the estimate.
What fuel cost should I enter for my location?
Fuel costs vary significantly by region and over time. For natural gas enter cost per therm, for electricity per kWh, and for fuel oil or propane per gallon. Contact your local utility or fuel provider for current rates, or check the U.S. Energy Information Administration (EIA) website for average regional prices.
What R-value should I target for my attic?
The U.S. Department of Energy recommends R-38 to R-60 for attics in most climate zones, and R-13 to R-21 for walls depending on your region. In colder climates (higher HDD), higher R-values have a better return on investment. The EnergyStar Insulation Map is a helpful reference.
How is the greenhouse gas reduction calculated?
The CO₂ estimate is based on the BTUs of fuel saved per year and the emissions factor for each fuel type. Natural gas produces about 117 lbs of CO₂ per million BTU, electricity varies by grid mix (~1.2 lbs/kWh average), fuel oil ~161 lbs/MMBtu, and propane ~139 lbs/MMBtu.
How quickly will new insulation pay for itself?
Payback period depends on the cost of insulation installation and your annual savings. Many homeowners see a full payback in 3 to 7 years for attic insulation upgrades, after which the savings are essentially pure profit. Adding this calculator's 10-year savings to your estimate gives a good sense of the long-term value.