I'm going to make a suggestion. Before you pour your concrete floor, put down either Pex pipe or even just 3/4" black plastic irrigation pipe.. even if at this time you have absoluetly zero interest in heating the concrete slab, you can for a few bucks have the option in the future..
Look at this to see what I did for my house project: My current huge project
Now you DO NOT have to get all carried away with manifolds, fancy piping etc.. my 40x60 shop has regular black plastic 3/4" sprinkler irrigation pipe burried in the slab, and it is 13 years old.. working fine.. there are good reasons to use PEX with oxygen barrier, but back in '97 when I poured the floor in the shop pex was very expensive.. so I went cheap, and haven't had any problems as of now.. I don't really expect any either. I don't have any ferrous metal in the system except for the two Taco 007 pumps.. and they are still doing fine, even though they should have rusted a lot by now..
If you look into a wood/coal boiler, look at the AHS multifuel,, they are in SW Penn. near you.
But I personally won't pour any concrete slab without adding pex or piping in it.. just keeping a slab at 55* makes for a very comfortable place to reload, have a beer, fix a car etc..