| The "water" heaters used for these applications are far smaller than those used for potable house water. They come in various sizes and shapes, some are floor mounted and others can be hung on the wall and powered by electirc. I believe that their tank capacity is relatively small too, 1-3gal. The system piping in total may use 20-30 gal., so there is no need to have a large home unit available to dump 130 degree water into the system all at once. The concrete won't heat up that fast anyway and the reheat time of a large unit is far greater.
Run a search for the user "ultgar", he has pictures of his system and is a garage outfitting/building (for lack of a better term) consultant.
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'00 Toyota Celica GT-S
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