This is a very controversial topic. (hot water) My opinion here. As long as the water doesn't get above 180 or 190 degrees you should be fine. I forget at exactly what temperature water boils at. No one in their right mind has their water heater set that high. Mine is set for 120 degrees and I wash my microfibers in that temperature with no problems. I use hot water because I feel the towels come out cleaner.
Just a side note here: I've boiled microfiber at 200 degrees for 10 minutes and didn't notice any bad effects. (no melting) I did notice color fading just a tad, but that was it. Mind you, this was done with a quality microfiber towel from a vendor.