i suspect the op has had quotes for different systems and they have been way more than what he thought and is looking for a cheap solution, of which he will have trouble finding.
his original idea was undersink water heaters
a barn conversion property isn't exactly going to be sold for peanuts, so invest in it properly op. how would you feel if you brought a aston martin and someone put a vauxhall corsa engine in it
I would check under the bonnet first, before I bought the Aston...having spend £250,000 CASH on it, I don't believe that's called peanuts, do you? The under sink heaters was just a question for 'so called professionals', but I see this is the wrong forum for that, I wanted impartial advice not people who just are intent on punting their own services. LOL
I really can't see why investing an additional £23K for a system when we will only use it for 6 months - would you waste £23K like that dean7445? I guess not!
I have some ideas now, so I will go and speak to the professionals WE choose to for a price.
Thanks to all for their biased opinion.