I agree, most boilers, left without proper tuning are running below 90% efficiency, most likely about 80%. A 10% increase at the country level would be significant.
https://blog.gcwizard.net/manual/en/summer-simmer-index-perc...
21.3 – 25 °C Somewhat cool. Most people feel comfortable. 25 – 28.3 °C Optimal. Almost everyone feels comfortable. 28.3 – 32.8 °C Somewhat hot. Most people feel comfortable.