Thanks for all the input Brewers.
What a conundrum. Cheap and relatively standard approach, but possibly ineffective. Or, expensive, but elegant and mega-effective option. I have to say with tap water at 1p a litre and a potential saving in energy it is looking like the latter.
My only issue is that with the new condenser unit, the seller states that you must have a power-adjustable boiler. My boiler has two power settings: one for boiling (3000W), one for mashing (1500W). Though it isn't power adjustable, it is temperature adjustable. So, I guess with a little experimentation I'll figure out where that boil point will be with the unit on and set it for that. Could even use the lower power setting.
Ummm. After doing the ferm' chamber, I think I know what my next brew-project is...