Where in the uk can I buy a small water-air heat exchanger?

Question:I want a small efficient water radiator that can be connected to a household boiler, and sealed in a unit to connect to air ducts as part of a small Heat Recovery Ventilation system: http://en.wikipedia.org/wiki/heat_recove...

Answers:
Try to get hold of a car heater core from a breakers yard. That's probably the cheapest and most available source. Otherwise they are going to be expensive.