"Steve" no.junk.mail@here wrote in message
...

What's the efficiency of a back boiler compared to a modern unit?

The claimed efficiency (at max output) of the Bermuda which I installed in
1969 was 77% (i.e. 40,000 Btu/h output for 52,000 input).

Interestingly, my 10-year-old Baxi Solo 70/4 PF has an almost identical
quoted efficiency - but that almost certainly doesn't qualify as "modern".

Hopefully others will quote figures for current production boilers.

I suppose back boilers do suffer from the additional problem that the waste
heat which is not transferred to the water goes straight up the chimney with
no benefit. At least the waste heat from the wall-mounted Solo helps to heat
an otherwise unheated utility room.

Roger