Enrichment · Passion Projects · Environment

What more insulation
saves, in fuel
and in dollars.

Type the surface, its R-value before and after, your climate and your fuel. The estimator works out the heat that stops leaking through, the fuel and electricity you no longer buy, and how long the project takes to pay for itself.

Estimate the savingsWhat you get

The insulation savings estimator

The worked example is a made-up attic floor in a cold climate with gas heat. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
Heat lost before and after, fuel and kWh saved, yearly savings and simple payback. It prints as a summary and downloads as a spreadsheet.
Who it is for
Families weighing an insulation project, physics and environmental science students, and student energy audit projects.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Measure the area: the attic floor, a wall or the crawlspace ceiling.
  2. Estimate the R-value now and after the work.
  3. Look up your heating and cooling degree days.
  4. Pick the fuel and type its price from a bill.
  5. Add the installed cost for the payback.

Estimate the savings

How the savings are estimated

R-value, degree days, fuel.

The worked example: an attic floor from R-11 to R-49U before − after0.07051/11 − 1/49Heat saved12.2 MBtu× 1,200 sq ft × 6,000 × 24Gas135 therms÷ 0.90 ÷ 100,000 BtuA year$212heating and coolingThe worked example: an attic floor from R-11 to R-49U before − after0.07051/11 − 1/49Heat saved12.2 MBtu× 1,200 sq ft × 6,000 × 24Gas135 therms÷ 0.90 ÷ 100,000 BtuA year$212heating and cooling
Savings follow the change in 1/R, so the first layers of insulation do most of the work.

R-value and 1/R

R-value measures resistance to heat flow; its inverse, U, is the heat that gets through each hour per square foot per degree. Going from R-11 to R-49 drops U from 0.091 to 0.020. Because savings follow the drop in U, the first few inches matter most, and doubling an already thick layer saves comparatively little.

Degree days

A heating degree day is one day with the average outdoor temperature one degree below 65 °F. Adding them up over a year measures how cold a place is: about 6,000 in Chicago, under 2,000 in Miami. Multiply by 24 hours and by U and area, and you have the heat that crosses the surface in a year.

Sources

  1. U.S. Department of Energy, Energy Saver. Insulation, R-values and recommended levels by climate zone (energy.gov/energysaver).
  2. ENERGY STAR. Recommended home insulation R-values (energystar.gov).
  3. U.S. Energy Information Administration. Heat content of fuels and degree days explained (eia.gov).
  4. NOAA National Centers for Environmental Information. Heating and cooling degree day normals (ncei.noaa.gov).

The worked example is made up. Real savings also depend on air sealing and how the home is used; check current rebates with your utility. Your entries stay in this browser. Support: team@caveatacademic.com.