Like I said you are NOT exposing a large part of the coil to steam so you are fine. If it is done properly you will be fine. This lab we work at demands it and this has been done for years with no problems. Just like so many things we do, if it is done properly you wont have an issue but you will find the exception. They also say dont use a pressure washer, we use it all the time with no issues. Pressure washers are more for speed and some applications are difficult.