It's hydro, but I did not add any anti freeze. You can, but I didn't feel the need. We keep the system on all during the winter of course, so there's no chance of freezing.
The best part is the boiler. It heats the water in the tubing in the floor as well as providing our domestic hot water. On demand, as they say. My plumber ran a recirc line and now I have instant, on demand hot water at virtually any faucet in the house. I highly suggest a recirc line for the size your building. Otherwise you'll wait 20 minutes for hot water.
**** Biden
I don’t know much about plumbing after the basics, but sign me up for this at some point.
Our house isn’t huge, but it’s a pretty solid inconvenience waiting for hot water in our bathroom. Its as far away as possible from the water heater. Not a big deal in summer, but sure sucks in the winter.