http://blog.visiondecor.com/index.php/2008/11/18/the-explainer-why-does-hot-water-clean-better-than-cold-water/The above link expalins why hot and cold are diferent in cleaning.
We all know why Pure Water cleans windows better than tap water, and the answer is that Pure Water is more aggresive than tap water and it also has less impurities in it than tap water.
So if Pure Water is aggresive when cold and we now know that when you heat up water it becomes more aggresive then it only logical that Hot Pure Water will be more aggressive than Cold Pure Water, and something this aggresive could cause problems on some materals.
I have had tee shirts that have developed holes in them quite quickly and the reason I know that its Pure water that is causing it is because I brought several of them and I only used a few for window cleaning the others I wore elsewere.
The ones I used for window cleaning devoloped holes while the other did not, It does not happen with every teeshirt.
I have noticed that in the summer it gets worser than the winter months, so it could be because the water is at a higher tempreture.
The same applies to the stinging of the eyes when some drops drip into my eyes, its stings more in the summer months than it does in the winter.
At the moment I use cold but I will be converting my system to hot soon, but I will be looking for signs of extra wear and tear on my customers windows and if I see any signs of damage occuring on them windows, then I will clean with cold.
As for Brodex bringing out a Hot Water system, well why not, hot water imo will only be damaging to a limited amount of customers houses, while the rest it will be perfectly ok for.
Wfp cleaning is a learning curve all the time, as more and more cleaners are using and modifing it, we come across new knowledge about wfp, and if we can learn from it then you can only get better at it.