Myths of gas central heating

I designed and installed my gas central heating with hot water storage cylinder 40 years ago.
For the average home, advice said fit a 60,000 BTU gas boiler (about 11kW) this was based upon the 'recovery' time of approximately 1 hour from cold.
I read a trade magazine which had a story from a retired gas engineer. He had his home fitted with a 40,000 BTU boiler but fitted as many radiators as possible and the largest size possible, much to his wife's annoyance. His gas bills were miniscule.
It's the total output of the radiators in each room that is the secret of low energy bills.
People complain the rooms are cold on winter days, and the boiler stat is set at a maximum about 80C.
In an experiment I found the following. The weather report at 10pm warned of snow in the night and below freezing temperatures all next day. So I set the timeswitch to constant and the boiler stat down to only 30C.
The following morning the house was warm and because I was home all day I left it running. I checked the gas meter every hour, it used 3kWh for the whole house.
When the hot water storage cylinder needed heating I turned the boiler stat upto 60C. The gas meter reading was 6kWh for the hour recovery (including heating).
The amount of water in the system: radiators, pipes and boiler is very little, a few litres and that is what the boiler energy is heating.
To have more, and bigger radiators is only a small increase in water, but radiator output is greatly increased for a small increase in gas used.
Rip-off installers fit radiators of about 2kW output per room, the optimum is 4kW
Another tip is to fit TRV's. The other end of the radiator is a water flow valve to isolate, regulate and balance the system. I have these valves just "cracked" open, this reduces the amount of water flow through the boiler/radiators and "warms" the room, rather than hot-cold room temperatures. The gas boiler operates more efficiently.

Hope this helps