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Since it's only hot air being exhausted and not engine exhaust gases maybe you could use some type of flexible ducting to direct the air away from your patio area? Of course you would have to make some type of easy connector and that would depend on the shape of the exhaust and how easy it is to access. This site has quite a few different types of lightweight flexible ducts. http://www.ducting.com/hose-types/fabric-hose/