Regulation Change - Ventilation is not just needed for stoves over 5 kW and fires over 7 kW.
As well as the kW rating of the appliance affecting ventilation requirements, installers and suppliers must also take into consideration the air permeability of the property when fitting a vent for a heat producing appliance. Building Regulations give guidance on how to tell if you have a requirement for extra ventilation. It is unlikely that a dwelling constructed prior to 2008 will have air permeability of less than 5.0m³/(h.m²) at 50 Pa unless extensive measures have been taken to improve air-tightness. So if you are installing or supplying ventilation products you must check on air permeability first as extra ventilation will almost certainly be needed in newer properties - its no longer the case of "Its a 5 kW stove or 7 kW gas fire so I don't need to provide ventilation".