In a Communal Heating Network (see What is Communal Heating?) each property in a development is fitted with an HIU and the heat is generated by a large central boiler.
The HIU can usually be found in the utility cupboard of each property, and looks like a large white metal box.
A Heat Interface Unit (HIU) fulfils the same function as a combination boiler providing heat and hot water, but without the need for each property to have a gas supply.
The HIU takes the heat generated by the communal boiler and uses an inbuilt heat exchager to heat the water in your central heating and cold water supply.
Each HIU is fitted with a heat meter which measures the heat and hot water being used by the property or apartment.