Odor issues

I need some advice for my buddy! He is having some odor issues at this moment. Here is what he has, It is A 12x12 room that house's A furnace. We have installed A vent fan and filter(fan and filter are rated for A 18x18 rm) but when the furn kick's on it stinks bad.... How often should he run his vent and for how long? (this is the flowering room)! And there is no CO2 being injected and another worry is what should he do in the summer to cool it? There is no AC at his house and we don't have the ability to put in A window shaker.... I need everyone from RIU to give him some advice since he doesn't have the chance to use the internet or doesn't want to I should say!!!!

Thank you everyone.