It's called combined heat and power or CHP. Usually used in district heating on a larger scale. For example Helsinki gets some of its heat from the waste heat

It's called combined heat and power or CHP. Usually used in district heating on a larger scale. For example Helsinki gets some of its heat from the waste heat of coal electricity plants. The electricity produced is also of course used. There are a few plants and the hot water is piped underground to the district heating grid that spans the urban areas. Further away with sparse housing it doesn't make sense. Basically, a heat engine needs a high temperature difference to make electricity. After that, there is still a low temperature difference left (100 C). That's still ok for heating houses. There's a lot of discussion how do you calculate the efficiency or climate effects. You can say the heat is waste and free and no climate effect. Or then that it's 100% fossil. CHP is an alternative to heat pumps. If you use wind or solar, they don't produce waste heat so CHP is not usable. Nuclear on the other hand would be a great fit for CHP, and is used for that in Russia. The temperature in the district heating grid is higher than what heat pumps would prefer but they are still used to create district heat to reduce fossil fuel use.