[Minimac]

I would agree that in a slab, it could work fine. I just think that, in the case of the OP and an old home, there are much better and cost effective options. Look at the manufacturers temp ratings on the tubing. High efficiency isn't worth much if it isn't cost effective. The goal of any heating system is to keep you warm when it's cold. If it can be done cost effectively, so much the better!