No Rob,
I was suggesting pipe on the 8 inch course of rebar, not 8 inch pattern.
Pipe cost less labor is 3,000x $.28= $840.00 toss a Sioux Chief manifold on if you want for another $50.
You can never place that in the slab at a later date.
The least expensive and best option is the perimeter footing. Even at 24x48 inches the concrete and rebar savings on the project are substantial when you as a builder are back at a 4 inch slab on compacted fill. 2000 sq feet at 10 inches =62 yards concrete
2000 x 4 inches = 24 yards @ $130.00 yard plus placing. Here is a number just for concrete 62 yds $8,060. 24 yds $3,120. (I assume the additional difference on the remaining 1,000 feet will be consumed in the additional footings.) My guestimate does not include rebar or labor savings.
Now with a 4 inch slab the system is in line with standard performance.
So I change my vote to advocating a standard slab, with $ saved buy solar,
Back to Sunday
Cheers,
Dan

whoops,
your right it is a 1,000 sq ft slab.
Still like footings, 4 inch slab
Dan

A further apology coming your way then dan. Note though, should you end up in this position again, that even 1000 feet of pipe is about the cost of the additional cost in many cases, which would do a far better job for solar heating than a separate set of pex loops. It's a bit of a non-starter for an idea. but again, I came on a bit stronger than was warranted: I do sincerely apologize. Not for the first or last time I'm sure.

Not being a concrete guy I basically have no idea what you're talking about structurally. I'll go with the earlier guy's post noting that for this kind of structural requirement, someone with a stamp (and a hefty insurance policy) should be calling the shots.

yea, it is the engineers job to design cement work, but earlier on he mentioned a 24x 48 inch footing alternative. I know as a builder the mono slab is simpler, as a heating contractor/designer the massive slab is to be avoided if possible. The 4 inch pour is preferred.

Blast shields are better with a Plexiglas window.
A few years back a French Buddie (timber framer ) had a wood boiler that was overheating, natural he removed some of the safety features, PR valve......
so were having a look, he builds a nice hot fire with a full charge of fir kindling, as she roared to life and started making these large metal noises we took the wine and found shelter behind one of the solid fir shop doors to the out side till the beast cooled down, All in all she probably would blow the pex first, but the noises made were impressive. He is back to a wood burner that does not have the boiler.......
Dan

I said "additional cost" instead of "additional coil" in my last post.

I've heard tell of many banging/creaking oddities out there. It's amazing what people will risk to save a buck. I think it was mythbusters that showed what a water heater can do if it blows... no stick built structure can stop it, it's a bomb. with most systems though you need multiple failures to make a rare occurance (massive pressure build) unsafe. In the wood coil systems, the occurrence isn't nearly as rare, and much less needs to fail..

In Seattle 2 years back local news covered ( after the fact) a water heater launch. Through the roof of the Pizza parlor up apparently 150-200 feet, then back to earth.
No injuries.
PRV valves are a good thing.
Dan

Actually, it's a 1480sqft slab, the main is 670sqft and the upper is 880sqft. The perimeter and bearing walls are a total of 285 lineal feet. Because of this bearing area, a 42"x24" footing would end up using 73 yards of concrete for the footing alone. The monopour of the thick slab is both easier and cheaper.

How long could you expect it to takethe slab to react to changes in temperature? Say the room temp was to drop from 75° to 70°, approx how long would it take the slab to react? Water temps can be up to 120°. I think we can live with a one day overshoot / undershoot. Our climate here tends to change week to week more than day to day. The supplmental baseboard heat will help make the air temp comfortable during any quick drops in temperature.

As far as solar goes, we have no tax incentives here, and the payback would be very long in this climate, so it's out. An outdoor wood boiler as an alternative to the gas hot water tank may however be in the future plans. We have lots of wood availible locally.

I have a 16 inch thick slab in a 40'X 40' building. Maybe I could help. The "heat up" and the "cool down" time takes much longer. The day to day change is minimal.

Did a few more calculations on this slab. It looks like with the large mass on concrete, and a 30K BTU input, the temerature could rise as quickly as 1°F per hour. So say the thermostat setpoints are 70°F on and 72°F off, it should kick on for about two hours at a time. There are only two windows and one door out from the basement section, and the heat loss will be quite low.

We'll put the tubing in the upper 2" @ 12"OC (rebar is at 24" centers both ways, so this makes it easy). Will have to see how it turns out, worst case scenario sounds like we'll have a tempered slab, and will end up relying on the electric baseboards to handle any sudden cold snaps.


Thanks for everyones input. Next question will be what sytle of loops to use, serpentine or spiral? My assumption is that it really won't make any differance from a heating standpoint. Any comments on which is easier to layout and install?

Well I can say I do this all the time. Heat thick slabs lol. And Ill tell you the best way to do it it take 2 times the pipe. You lay your pipe like you would in any slab execpt you do two layers on each zone. one at the bottom like normal and the other at the half way point. It takes time to set up but pays off in the long run. It dont cost much more to heat the slab then it does 4 inch slab once its heated up. And yes the cool down takes longer also.

Im building a building now for a tracktor shop. its 130x80 with a 24" slab. That one is going to get done the same way.

P.s I lay the pipe at 16" each loop. top loop is off set so when looking down at it there is a loop every 8"

snicks,
I like this idea, so you are laying pipe on the slab insulation , and the 4 inch level, or the 2 and 6 inch level? are you running 3/4 pex 500'? or 1/2 330'??
Dan

 Hello, Yes It will be layed at the 2 and 6 inch level on a 10 inch thick slab. And as Pipe size goes it depends on the size of the building. I Preffer 1/2 at around 300 yes. I have done it bolth ways (3/4 @ 500)and works just as good. But the pipe and fittings are alot higher for 3/4

On the 130x80 building that im building now will have a 18 inch slab it it. And it will be at the 2 inch mark above the insulation and around the 10 inch mark above the insulation.  ( I miss posted it as a 24 inch slab sorry about that)

Also the slab is poored all at once not in steps.

I run a 1 1/4 feed to the manifolds also supply and return. I custom build my manifolds for every job. I do not buy them.


I have been doing it this way for a long time now. Im not sure if any one else has done this before. But I do know my systems out preform my competitors in my area.