Worked out, so you don't have to take my word for it.

The four types, what each costs to run, how big you need and what a fair install price looks like.

Gas, electric, heat pump and solar on one basis, at your tariff, with the install cost ranked against the running cost.

Why bedrooms are the wrong measure, what a mixed shower really draws, and why an off-peak tank has to be bigger.

The flue clearances from AS/NZS 5601.1, drawn one at a time, with what each distance is measured between.

Rinnai, Rheem, Dux, Bosch and the air con brands, taken from the manufacturers' own manuals - plus how to get the code out of a unit that only flashes at you.

How kilowatts are worked out from a room, and why both undersizing and oversizing cost you.