We have radiant heat in a slab. In fact, it's our only heat source (outside of one gas insert). I almost didn't buy the house because of it, as I couldn't imagine how the system could sufficiently heat the house if the temps went to 0F or below. We're at 6200 feet, so it happens. This is now our 5th winter in the house and the radiant system still amazes me. Not only does it easily keep the house at 70F if we choose (we normally use 68F), at 4F outside and high winds (just happened in this storm that eventually hit Texas), it does so silently, and we've never had a natural gas bill higher than about $220 for a 3650 sq-ft single-level house. Since the only electricity it uses is a control board and a small pump, I can easily use one of these:
Buy a Duracell PowerSource 660 - UPS - 1440 Watt at CDW.com
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To keep the entire heating system running for about a day, assuming the gas isn't affected. Each room and bathroom has a separate zone which is nice.
One weakness of radiant is that it likes tile or stone floors best. If you have carpet you really need to use low-pile dense stuff with rubber padding. When we bought the house several rooms were carpeted with a short shag (considered fashionable in 2006 when the house was built; ugh) and foam padding. Using rubber padding and low dense pile as the boiler company recommended made a big difference in heating efficiency.