Meauring energy consumption

Is there any meaningful way of working out how much energy is being used in a section of a building which has it's own DHW supply pipe and CH supply and return.

I'm trying to work out whether to have put in one large boiler in my commercial downstairs property and feed our flat above from it or use a moderate boiler downstairs and a smaller one upstairs. This would save a considerable amount of money and ongoing cost.

Ay helpful comments gratefully received

Anyone know about heat meters?

A company called S.A.V systems use them in their substations.
A substation may suit what you want to do but for a single one, the two boiler route may be just as cheap.
The Danfoss Sonometer records the energy used.