It pays to insulate

Back in November, I hired a handyman contractor to do two things: Fix the rotten wood on the roof, through which I suspected that mice were entering the house, and insulate our attic. The latter was something of a large job, as it involved removing the 50-year-old blown-in insulation, laying batts of modern fiberglass insulation, and laying a wood floor (for storage) over the new insulation.

After inspiration from a WSJ article sent to my by a friend - you know who you are - I decided to calculate whether my investment had paid off. I looked up government data on "Heating Degree Days" for Washington DC over the past three months, and compared it to my gas bills for the same time period.

Now, there are a number of reasons that this is unscientific:

• The insulation was added in mid-November, so the full month of November isn't really a fair "baseline".
• The weather data is based on the calendar month, while the gas bill is based on my billing cycle month. While they overlap for the most part, they aren't perfectly aligned.
• I based the home heating expense on dollars, not BTUs purchased from the utility - so any variation in natural gas prices during this timeframe would skew the results.
• This was an unusual time period for our house, since we had houseguests frequently staying during the week (when the thermostat is usually very low). If anything, this caused us to use MORE heat than would be typical for December and January.

Nonetheless, one thing is pretty clear: It got much colder outside, and our heating bill went down!

The data bears out my experience. Previously, the furnace was working very hard to heat a poorly insulated house. As a result, the temperature difference from downstairs to upstairs was routinely 5-10 degrees. Now, upstairs and downstairs are typically within two degrees of each other. And the furnace gets a lot more time to rest.

One more benefit: No more rodents since the roof was fixed!

Major hat-tip to Sam and Sons Services, who did the work. (Yes, their website is a little weak total disaster, but they do good work!)