wrote in message
oups.com...

And therein lies the problem. Using your boiler just to heat HW

and requires minimal energy to maintain optimum water
temperature. A gas boiler can be as low as 50% efficient when
heating just the copper cylinder.

please tell us which new gas boiler is 50% efficient. And when and why
one would heat just a copper cylinder.

Although I think gas does still win out, all the energy from the electric
immersion heater goes into the water whereas running up a boiler 'from cold'
means it has to heat itself, it's piping and so on as well as the water.
But I still think gas works out better simply because it is so much cheaper.


The system has a warm up period
where no heat is being transferred.

yup, same for immersions. Measured in seconds in both cases.

No - electric is seconds - gas is minutes.