Hi Guys,
I have been using a tube in tube exchanger for a few years now. On about 8hp, with around 2kw load, the 3m long exchanger heats up 300L approx from around 15C to 75C in about 2 to 3 hours.... Currently we have the lister down for rebuild and have been using a babbington burner on a 700mm long exchanger doing the same job, but burning about 30 to 40% more fuel for the same time period... the bab puts out way more heat, much more goes to the stack because of the short exchanger, but in most more ways, better to run from a heating pov if electricity is not needed...
Cheers
Ed