only when i find the fan isnt cutting it! i prefer not to use them (only got them in a few weeks ago cos heat plus pg ms didn't go together at ALL) - but having found that today i got hot around lunch and am having to use aircon, i will probably put it on a bit earlier tomorrow - getting overhot BEFORE putting it on defeats the purpose IMO....

judge for yourself - if you can keep the house shut up and air movin, it's probably not a necessity - but if you find you're getting uncomfy, go for it - no point suffering!