We inherited an Aga when we moved into our house; it used to be coke fired but had been converted to gas. Generally speaking it's great and I enjoy cooking on it (and it heats our water for us) BUT it uses a lot of gas.
This scheme uses an arduino type microprocessor with a servo to turn the temperature control right down at night and during the day. The Aga takes about three hours to heat up or cool down but I reckon it must be saving quite a bit of gas (data to appear here when I have collected and analysed it!)