Re: cold water hydro?

A COLD cold water hydro is inadvisable due to the chance that the steel may become brittle if stressed up at too low of a temperature. The current standard is to heat the water to at least 72 degrees before pumping up the pressure. This is easily accomplished by sticking a salamander heater in the fire door for a few hours, with a meat thermometer stuck in a telltale hole low on the firebox.
A hydro before removing the tubes is a good idea as a way to check for other problems that are better found before the new tubes are in, such as cracks in the firebox, leaky seams, etc.