On Tuesday, 31 December 2019 14:22:06 UTC, Tim Lamb wrote:
In message ,
tabbypurr writes
On Tuesday, 31 December 2019 11:49:12 UTC, Tim Lamb wrote:

I assume boiler efficiency is non linear.

efficiency versus what is nonlinear?

Efficiency related to boiler output.

I expect it is.

Given that a fixed amount of
energy is required over a 24 hour period, and that boiler losses only
occur during firing, my uncertainty is whether a shorter firing period,
but at reduced efficiency, would use less gas overall.

If you need say 24kWh dumped into the house over the day, you could run
the boiler (making up rounded guesstimated efficiency figures) thus:
1. 4kW output for 6hrs at 90% efficiency, thus consuming 24kWh/90% = 26.66kWh
2. 24kW out for 1hr at 80%, thus consuming 24/80% = 30kWh of gas.

In practice the efficiency difference is probably greater than that.
Losses when off are not zero but relatively trivial.

OK. Are such examples searchable for a particular boiler?

I've not even looked. I suspect boiler mfrs probably just quote their best possible headline figure and say nowt else. Anyway efficiency is always going to decline as P_out increases for a given heat exchanger.


NT