George, they make a round hole thru a building block and place some kind of small box on the outside wall. The vent goes right to there and stops. No chimney required. It's rather like the clothes dryer vent, or the kitchen stove exhaust fan vent on the outside wall. We HAVE to do something for the very reason that in the summer time, when the air conditioner and the hot water heater go on simultaneously, fumes come into the workshop, plus condensate backflows into the furnace vent and rusts out the doggone furnace! This doesn't happen in the wintertime because of the cold air being outside and the warm air inside. It happens in the summer because of the cold air being inside and the warm air being outside. The exhaust from the furnace has to flow thru a 20 foot transite pipe before it finds the chimney! The house was not built to take air conditioning. BTW, we are both delighted that your shoulder feels better! I don't dare tell you to take it easy, but DO be careful! Penny, NY . . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/tagj.