LsFarm wrote:I'd do this:
Run the hot water and map the pex locations.
Cut core sample holes as suggested, inspect the core of concrete, and check for well compressed substrate sand/gravel.
Drill 4-6 similar cores, fill with concrete filled tubes, make these pilings part of a pad supporting the chimney..
OR go with whistlenut's suggestion, just put the chimney on an outside wall and live with the compromises of a non-central chimney.
OR if you feel lucky, just put up the chimney..
When I poured my heated slab in my 40'x60' shop, I made two pads, with deeper concrete and extra rebar. I think the pads are 8" deep and the
rest of the floor 5-6" thick. I used 5bag mix and wire reinforcing mesh to tie the tubing down and to create the grid of tubing.
On these pads i installed my above ground car/truck hoist, I've had 12K on the hoist several times.
IF you spread out the load, as suggested you will have a lot of surface area to carry the load, and as suggested, figure out how much your chimney will
I sure would sleep better knowing coal was heating my home than a 12K condensing propane boiler! Eddie, I also like Greg's proposal (Hell,he started the damned rodeo and has been lucky enough to not have broken too many bones)....map out the pex grid (should be 12" OC in the middle, however who knows if they made criss-cross diagonal runs where you want the chimney. If you can locate the the grid, I'd core as large a hole as you could in a grid pattern between the layout you find, remove the sand/gravel/stone under the slab area with a post hole digger until your blisters bleed,(or if yuo know a guy with a Vactor Truck, no blisters) then install L rebar down to terra firma through those holes and pour a 4000 lb pea stone mix and use a vibrator to consolidate the incoming crete. That will make multiple piers that are reinforced and support whatever void you create while digging the grid out. If you stay inside, this will work VERY well, be cost effective and perhaps you will never touch a pex line.
4000 PSI structural columns, assuming a 3000 or 3500 psi floor....perhaps 1/4" 6" by 6" mesh, perhaps #10 mesh...... When we do sono-tubes, we pour a 2' by 2' footing, add 4 'j's 12"l's by 3' long, tie 6" 3/8" hoops at 12" OC vertically, and I can assure you it they want to move that little tube later it will come out as a unit. You can hit it with a dozer or excavator,and it will stay there. Anyone out there ever seem tubes poured the correct way.....didn't think so. This is residential and lite commercial'
Commercial is #7 bar 6" OC and # 5 hoops 6" OC. dynamite will fracture it but not remove it.........so I think you have the solution at hand. Get some antifreeze piped through it if you are doing it this time of year, or wait for warmer weather. The coring guys aren't real busy for the next 8 weeks.
Wow, This has been a very long road....But today I closed on the 30' X 40' Barn...
We now have a Anthracite Coal Barn.
Greg, We are going to use your idea and map & core the floor.
W.N., Thanks for all your info and help with this.
I have a Burnham oil boiler that will vent through the basement wall and the mason will build a two flue 8" X 8" block chimney up through the center of the building.
I will heat the building with 2 coal stoves this winter and try to buy a used coal boiler as long as my $$$ hold out....