I've never noticed a problem, been brewing BIAB for about 2 years now. Yes there's a fair amount of steam but I run the cooker hood when doing the boil, and I keep a window or two open (the more the merrier in summer!)
I've now switched to a digital electric boiler & built a new
brewhouse shed to use it in - but since I built it, I've only had time to do 2 brews and both of those have been demo brews at my LHBS!
mogrim - ambient temperature is more of a problem during the ferment - lager yeast prefers 15deg or lower, ale yeast can tolerate up to about 25-27 but above that you can start getting odd flavours.
if 20deg is your peak temperature then it'll be fine for ales and for some lager yeasts but not for all lager yeasts; the yeast will say on the pack what temperatures are ideal.
at 20deg an ale will be fermented out in at most 2 weeks. at 15deg a lager will take a bit longer. at 10 degrees you'll need twice as much yeast to start and it will take quite a bit longer...
For brewers in warmer climes, a brewfridge is a good tool. I don't know the full details, but basically any old fridge, with cooling and/or heating inside, thermostatically controlled to a temperature of your choice...