Did we save oil by insulating our attic?

In December 2018, at great expense and complexity, we insulated our attic, removing decades old asbestos insulation and replacing it with R40 of blown fiberglass.

Did it help our energy consumption?

Here’s a comparison of our 2018 and 2019 winter season oil bills:

Home Heating Oil Usage, 100 Prince Street, 2018 vs. 2019
Month 2018
Oil Usage
(litres)

2019
Oil Usage
(litres)

Change in
Oil Usage

January 541 527 -3%
February 914 937 +3%
March 452 418 -8%
April 505 471 -7%
TOTAL 2,412 2,353 -2%

Oil usage information alone doesn’t account for differences in heating due to differences in the weather; with the help of Efficiency PEI, I determined that there were 2,391 heating degrees days in the first four months of 2018, and 2,567 heating degree days in the first four months of 2019, suggesting that, all other things being equal, we would have used 7% more oil in 2019 (about 2,580 litres).

But we actually used 2% less oil, so our net oil savings due to insulation was closer to 9%.

Our home heating oil cost, because of the increase in the price of oil, doesn’t reflect savings, but rather a 2% increase:

Home Heating Oil Cost, 100 Prince Street, 2018 vs. 2019
Month 2018
Oil Cost

2019
Oil Cost

Change in
Oil Cost

January $491 $481 -2%
February $806 $875 +9%
March $405 $400 -1%
April $467 $463 -1%
TOTAL $2,169 $2,219 +2%

Had our consumption not dropped due to insulation, we would have spent about $2,348 on oil in 2019, meaning our net cost savings was about $129.