On Monday, 14 November 2022 at 12:40:11 UTC, Carlos E.R. wrote:
> On 2022-11-14 01:27, Commander Kinsey wrote:
> > On Thu, 10 Nov 2022 12:07:43 -0000, SteveW <st...@walker-family.me.uk>
> > wrote:
> >
> >> On 09/11/2022 00:14, Commander Kinsey wrote:
> >>> On Tue, 08 Nov 2022 12:35:03 -0000, Max Demian <max_d...@bigfoot.com>
> >>> wrote:
> >>>
> >>>> On 08/11/2022 01:22, Commander Kinsey wrote:
> >>>>> On Mon, 07 Nov 2022 11:27:33 -0000, John Larkin
> >>>>> <jla...@highlandsnipmetechnology.com> wrote:
> >>>>
> >>>>>> We heat our kettle with gas. All that heat winds up in the house,
> >>>>>> which usually needs it. An open flame is a more efficient heater than
> >>>>>> a gas furnace; no heat is vented.
> >>>>>
> >>>>> Even resistive heating is better than a furnace. Except for gas being
> >>>>> cheaper for some reason.
> >>>>
> >>>> I find it hard to believe that you don't realise that this is due to
> >>>> the
> >>>> Second Law of Thermodynamics.
> >>>
> >>> I know why it happens, just not why people use a furnace with gas. It's
> >>> a waste.
> >>
> >> The highest efficiency gas fired power station is aroung 62% efficient..
> >> Then there are 5% transmission losses.
> >>
> >> A condensing gas boiler is over 90% efficient.
> >
> > Then why don't they make the power station like the boiler?
> Because the exhaust gasses can not be colder than the hot water output.

A crossflow heat exchnager can get the exhauset gases down to approx the temp of the returning primary water, which is well below the primary boiler output temp.

There are also ways to take this further, like routing the semiwarm exhaust across the bottom of the HW cylinder, or through a single radiator used to extract this last bit only.

> For heating a house 60°C or less is good. For hot water, 45°C is enough.
> For a power station, you need to boil the water at elevated pressures.

More heat extraction makes sense at power stations, as it's far more power run more of the time.