Just to clarify - when i say unflued gas heater - I mean something like this http://rinnai.co.nz/Subcategory/21/portable-heaters Not those LPG botttles which are both very expensive to run and potential death traps (from the fire hazard). So yeah that is an issue if you are in the South Island.
BTW according to Rinnai :
I’ve read that unflued heaters require room ventilation when using, what does this mean and doesn’t this defeat the purpose of having a heater on?
Unflued appliances draw the air for combustion from the room itself. This can lead to a build-up of moisture if the room is not adequately ventilated. Unflued gas appliances need to be used in a well-ventilated area with plenty of fresh air circulating (a partially open window is ideal). The heaters are powerful enough to heat the room and there is only minimal heat loss through ventilation.