Yo dude, i think
Going2fast is on the right track with the fact that the main issue is the light is likely too large for that tent - if it's 3ft by 3ft than even an 800W CFL would be unnecessary, let alone COBs - if you're struggling to keep it at 28°c with everything blowing then that's an issue - i would suspect that your extract fan is actually removing a load of heat already and if you turned all air systems off the temps would probably hit near 40°c. I can't see on your posts you specifically mention how hot lights are, though from description I'm assuming they are the source of heat issue??
I've never used any LEDs myself though from reading enough of other peoples issues i know COBs run hot as standard & 800W would be designed for use in a much larger area than 3ft x 3ft. Plus, if you bought some MiC special off Amazon, then their non-existent heatsinks & shitty drivers mean thermal output can go uncontrollably high. If it's a proper brand name, quality unit and it's burning hot then it's possibly component failure & needs replacing - It's not a great solution for right now I'm sorry to say, though i would agree different light unit would solve the whole issue going forward.
Secondly, i was just wondering about your room set-up and are you able to just have the window open during lights on period?? Not being a clown, but it did make me chuckle that you're having trouble cooling a room in the middle of a Canadian winter! Is it possible to insulate that room from the rest of the house and just let the temperature drop in that room via the open window? If you could, then it would allow you to just intake & extract into cold room, and naturally cool tent down too.
If not able to do this, and to answer your venting question above, yes you can intake & extract through same window, though try to space them apart from each other as much as possible and, if you can, tilt their opening faces away from each other just to avoid any hot extract air being accidentally sucked back in. Air from outside atm is going to be the coldest so i would say is best bet for combatting heat, though i think overall a new, less powerful/more thermally efficient light would save you even having to mess around with air extraction.