Comment by pcrh
Up until the late 20th century, British homes were very poorly served for heating during their long damp winters. No insulation, no central heating, etc.
Coal was the usual source of energy, and coal fires were usually continually burning, being "banked" at night. In this context, the "always on" AGA was not so unusual.
So the AGA stove served not only as a cooker, but also as a source of heat, similar to masonry heaters. Many were also connected to a hot water tank.
The sales manual above states that the cost of running an AGA stove in 1935 was £4 per year, or £247 (~US$330) per year today.