Bubba writes:
Seems you've already made up your mind but I'll give you my .03
worth. I previously worked for a national hvac company that adopted
this practice like it came from the bible. This company was also into
high pressure sales practices and tactics. One little twist they added
to the test was to make sure the heat exchanger was nice and hot right
before they started spraying water on the heat exchanger. Common sense
tells you that hot thin metal and cold water are not a good
combination for a homeowners heat exchanger. CO tests, detectors and
visual inspections and cameras are a more advanced way of checking
heat exchangers.
Bubba

Thankfully this company didn't do that! Since it's still a bit
A/C season, he didn't want to run the furnace to put the HX through
that thermal stress, but he did clean the burners and everything and
then was curious enough to do the inspection. It was done with a
room temp HX. He did a visual with mirror but I don't think I saw a
camera involved.

Tis interesting though how many different ways there seem to be to
check HX's.

--
Todd H.
http://www.toddh.net/