What size are the coolant hoses to heater ?

Can anyone advise what size the inside diameter is of the coolant hoses that connect to the heater matrix ?

Do this mean you are going ahead with a veg oil conversion?

Yes going ahead with the conversion, i've a webasto heater i use to preheat the engine & veg oil heat exchanger. This starts up via a webasto timer before / after work and takes only 20 minutes to heat everything to running temp. (added benefit of a warm car during icey weather) I can then start-up on veg straight away, and this heater only uses .1 Litre of diesel per hour. Had this system on my 300 tdi 10,000 miles and cost me nothing (20 quid in diesel or so) as i get used veg oil free..