For hydronic heating applications (ie. circulating hot fluid through a network of tubing or radiators - sounds like you are doing a radiant in-slab system) the "professional" solution is a condensing boiler for a small system which it sounds like you have. They are very efficient and don't have a high BTU output, no need for primary/secondary circuits or mixing valves, etc. I used a Triangle Tube Prestige Solo 110 boiler which has an integrated circulator hooked directly into my floor loops (via zone valves controlled by slab stats). Nice simple setup and relatively easy for the DIY'er. You can wall mount the boiler and up 7 ft. is no problem because everything is accessible through the removable front panel. Here's the specs. etc.
http://www.triangletube.com/CondensingBoilers/PrestigeOverview.htm
These boilers have a unique heat exchanger design that will last for 20-30 years before it dies. Much more reliable than just using a hot water tank or something. Might be overkill for what you want though, I am heating 2000 sq. ft. with 3 zones. Might try talking to a local hydronics supplier to get their recommendation - they do this stuff everyday. You might be able to get away with just a tankless hot water heater (Paloma, Bosch, Takagi, etc.) and a small circulator pump.
