I have a generator exhausting through a pipe about 50% larger than the original exhaust stub and about 12 ft. long - no problem. Intake as above is fine, just remember that an intake generates a bit of noise as well. The big problem is static heat build-up around the engine if in a relatively sealed room. Good ventilation is essential or you could have the whole lot catching alight on you (generators generate more than electricity, they generate a considerable amount of heat too, especially under load).