Originally Posted by smoke and coke

i dont see any problem with that as long as you have enough fresh air getting into the spare room to replace what your taking out of it.
do you plan to run a duct through the attic to the outside? or just vent into the attic? since you have a filter there is no smell but you still have the heat going into the attic if venting into the attic. you could get an attic ventilator with a built in thermostat and set it for 100 degrees F. so it will cool the attic off a bit. i dont vent into the attic but i have an attic fan anyway to help cool it down so my central air doesnt run so much.