It is compulsory to have a 100cm2 ventilator for the room (which means its physical size is greater than 100cm2.
Flueless gas fires do not have a temperature control, they are either on or off.
Between the two things above its not really worth having one, electric probably works out cheaper once you take out the heat lost through the ventilator and the lack of control.
If a ventilator is put in, it must be lined so that it doesn't expose the cavity in the wall - we had a cowboy not do this properly and it went from a naturally warm house to one that was difficult to heat.
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