Our temperature sits around 21-23°C (70-73°F), but we rarely use heater. Under my flat is petshop which keeps us warm for free (not really, cause billing is complicated, but it's cheap - under $300 a year)
Also our building is recently (7 years) renovated and insulated.
Heat is made as a byproduct in coal "co generation" power plant and delivered through hot water pipe.