Some delayed switching it on by almost a month and set the temperature lower.
The data comes from the Munich-based firm Tado.
It has hundreds of thousands of smart thermostats installed in households across Europe.
People and businesses use more such devices now to see how much gas they are using.
Germany has even made them a requirement in newbuilds.
Tado found that this winter it took until November 28 for 90% of European homes to switch their heating on.
That threshold was passed weeks earlier during the previous three years.
Tado's data also showed home settings averaged almost a degree lower this winter than in prior years.
In the UK nearly 80% of homes turned down their heating.
That may show people have listened to warnings about possible energy shortages and soaring prices, which rose sharply last year after Russia invaded Ukraine.
The EU imports 80% of its gas, and has made big efforts to bring down reliance on Russian gas.
While authorities have raised sourcing from European gas producers like Norway and the Netherlands.
