Especially when workers are under the truck.
You application is small Square footage, I'd say go with floor. Overhead manufacturers have all kinds of disclaimers for being X No. of feet away from combustibles, etc.. they are a lot of hose reels, light fixtures hanging from the ceiling and MOST IMPORTANTLY the travelling Overhead Crane which will for sure be in the way of your overhead radiant heaters supports.
Need to watch for close coordination with plumbing, have them use a french drain style between the radiant floor bays in the facility which would lead to a sand trap (you know, they use this sand to soak in the spilled oils), warn the plumbers not to use floor drains, they will be clogged with sand.
Your 9,000 SF will cost about the same if you were to exlude the concrete assuming its a new job.
Go to
they have some nice slab details.
Use condensing boilers, they love the cold water return (90F) temperature from radiant floors, you would be getting 94+% efficiency.
OK, may be not if you are in California, PEX tubing is not allowed there I've heard (there's been an issue between PEX tubing manufacturers and the state of California).
The other thing you can do is use combination CO/NO2 sensors to energize a heat recovery unit for ventilation instead of having the units run continuously in winter. Use radiant ehat as primary heating medium, HRU as secondary. In idea is that if teh air quality is good, no need to bring in outdoor air. And you have yourself a LEED facility.
Good luck
