I'm currently pondering what the options might be when the time comes to
replace our elderly heating system. Since we're on oil and wood, it isn't
immediately obvious that a like-for-like replacement is the way forward.

Are there any tools around to help select what might be plausible options?

I came across:
https://homerenewableselector.est.org.uk/
which is quite good at doing an overview of various energy sources and their
likely yield and RoI. However it only works for Scotland - seems like they
didn't get their funding renewed for E&W and NI. That aside, it looks
useful if you put in a Scottish postcode and expect to tweak the numbers for
latitude and available grants.

However, what I'm more interested in is a bit more detail. For example, a
particular solution will need a 1000l thermal store that will cost £x, a
37mm pump £y, a controller £z, and if straightforward it'll take three days
to fit. Is there anything out there that will spec out what a system might
need, especially more complicated ones (solar hot water, ASHP, back boiler
on the stove, ...)? It doesn't matter if things aren't costed, but at least
a vague shopping list would be handy to price things up later.

Of course I could go to an installer for this. But I'd like to know a
little more before going and being sold their favourite one-size-fits-all
solution.

Are there design tools out there that the installers use, or do they just do
it by hand?

Thanks
Theo