John,
I have not experienced a noticeable difference with hot water house washing. I have tried it and had the hose burn Walt and Mark are talking about. I feel that hot water probably puts a little more wear on the hoses and guns. I have had the last section in my extending wands bend due to the hose heat inside the aluminum tube softening them up. Not to mention the added costs of running the heaters, and not necessarily just the fuel costs either. If I felt it made enough difference then I would use it. On those 95 degree days, I like a little cold water mist now and then.
Glenn

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"Hmmm, If everyone has a photographic memory... mine must be out of film."