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House Insulation Calculator

How much insulation should you have in your house?

This page calculates how much insulation you should have in all above ground surfaces in your house, given no building constraints. It should be noted that this calculation (unlike most governmental recommendations) contains no hidden assumptions or predictions, all predictions can be entered by the user.

The basic idea here is instead of picking a construction method and trying to squeeze the most r-value out of as you can, to start with the amount of insulation which is most economical, and then choose a construction method which allows that amount.

This calculator uses javascript, so you will need to have that turned on (sorry!).

House above ground1 surface area: 2 square feet
Heating Degree Days3: per year.
Heating Fuel #2 Fuel Oil (Gallons)
Natural Gas (Cubic Feet)
Electricity (KiloWatt-Hours)
Propane (Gallons)
Kerosene (Gallons)
Wood, Hardwood (Cords)
Wood Pellets (Tons)
Wood, Softwood (Cords)
Heating fuel price (per unit): dollars.
Heating system efficiency: percent.
Predicted fuel inflation4: percent.
Predicted income inflation5: percent.
Loan interest rate (or opportunity cost)6: percent.
Length of loan (or expected lifespan): years.
Type of insulation: Dense packed Cellulose
Loose Cellulose
Fiberglass (batts or loose fill)
Icynene spray foam
Urethane spray foam
Polystyrene, Extruded
Polystyrene, Expanded
Whole Wall factor 7: percent.
Existing insulation (or from structural components)8: R-value.
Free Heat (passive or existing solar)9: BTUs per year.
Insulation fixed costs10: dollars per square foot.
Insulation variable costs (per inch of thickness)11: dollars per square foot.
Results: R-value of optimal insulation.
inches of insulation of given type.
dollars per year (average combined fuel + loan payments)12.
Fuel units required per year13.

  1. Below ground calculations are more complicated, and best done separately.
  2. Add up all walls and attic surface areas (anywhere there is or will be insulation). Or just do some portion that you are interested in.
  3. Look yours up here (given Portland, ME)
  4. Take your best guess. The given value is for 1946 through May 2008 (adjusted for inflation)
  5. Take your best guess how much you expect your income to increase per year.
  6. Interest rate assumes a fixed rate with monthly payments.
  7. Given value is for 2x6 construction 16 o.c. with no foam sheathing.
  8. This can represent sheathing, siding, wallboard, etc.
  9. This is an advanced option, leave at 0 if you don't have any idea.
  10. Fixed costs for building constraints could also be added in here.
  11. Variable costs for building constraints could also be added in here. Given estimates are from I&S Insulation Inc. for dense pack cellulose.
  12. This figure represents costs for conductive loss through walls and ceiling only plus mortgage costs for same. Other losses include air leakage, loss through foundation, and radiative heat loss.
  13. This figure represents fuel required for conductive loss through walls and ceiling only. Other losses include air leakage, loss through foundation, and radiative heat loss.