Slab On-Grade Radient Heat Tubing

If the tube is laid out in a zig zag with smoothy rounded curves at the end of the straight runs and it isn't tied down tightly or constrained too tightly then there should be plenty of room for a bit of flexing. I don't think the expansion of each straight run will ammount to much, a bit of bowing in the run will allow it move if necessary.
I don't think there's a problem.
I tied down zigzags of 10mm copper on my solar panels with twists of plastic coated steel wire and there were no problems there with even with a pretty high delta T.
Del

Yes, Del is correct.

Here's a handy web site that allows you to calculate the amount of thermal expansion/contraction for various materials.

Unrestrained Pipe Expansion Contraction Design Equations Formulas ...

The foam should not be load bearing. It will collapse over time. Also the system would be more efficient if the tubing was above the 3/4" plywood flooring. Most are floated into thin layer of some type cement. It would allow better conduction of the heat into the room. If under the plywood in the air you would be heating the air first. Wood being a pretty good insulator.

Uponor (formerly Wrisbo) recommends limiting PEX runs to 300' so you should be ok.

I have installed PEX tubing in poured jobs and staple ups and worry about abrasion from expansion and contraction, but have not had a problem yet. Somehow I have always failed to as the question when in seminars and talking to reps'.

Being only a garage I am sure you will have the mixing valve set way back to only melt the snow and take the chill off so I don't think you will have a problem.

My own house is a staple up. Even though it creaks when starting during a cold start up, it is a nice heat. Everyone who has one also says so, although some of the installs leave you a believer in codes and standards. Some of the earlier jobs were pretty sloppy workmanship.

Uponor has a plant in Minneapolis MN (Lakeville or Apple Valley actually). Get one of their design manuals.

What is especially interesting about the Uponor system is their joint techniques. It is a plastic sleeve affair that contracts. Real neat, simple, and they the best - Maybe so!

My existing hot water boiler will be used to provide heat to standing radiators. The 2000sq ft house is set up on a single pump. I have to check it's current temperature setting. I'll probably need to do some more planning in this department.

http://item.mobileweb.ebay.com/viewitem?itemId=200259917986 Here is a guy on eBay selling product very afforDably.

The e-bay PEX looks like the product the building supply company from Wisconson called Menard's sells. I have always used Uponor or Heatlink, but I have noticed of people buying Menard's infloor heating products on several occasions.

They say it has the O2 barrier which is good, but be sure to put in a good air vent somewhere near the boiler and compression/expansion tank anyway (however, I am not sure that O2 will come out of solution anyway).

It will heat the floor, that is for sure.

I can't say I am an expert in this area, but I did something similar in my house. I am heating a 1500 sq ft house with radiators. I have the temperature setting at 180F. I remodeled my kitchen and bathroom and decided there just wasn't room for the radiators, opting for in-floor heating. The first winter, I found my floors were still pretty cold. The problem was that the pump only turned on when the boiler kicked on. The boiler only kicked on a couple times a day and it didn't take long for the PEX tubing to cool. This summer I put an inline pump on a separate switch for the radiant floor heating, hoping that I could pull the hot water from the radiators without kicking on the radiators. So far so good and my floors are kept at a very comfortable temperature. I haven't seen a rise in my heating bills so I am pretty happy with the result. Once again, not an expert, just an IE who likes to tinker.

Although I know it is less than ideal, my stapled up bathroom PEX tubes are buried under tile, thinset, cement board, and wood floor boards. Believe it or not, it still is pretty effective. Also, no issues with expansion/contraction in either floor.

Best of luck!

Interesting idea.

I'm in a long term effort to convert my house from central forced air heating to hot water. I had appropriate supply and return pipes installed to the upper floor when the house was built, and I sort of anticipated putting in baseboard hot water one day. Now I'm wondering whether radiant heat tubing would be a better approach, but a key question is how much protection the tubing needs.

I wouldn't want to replace all the floors (mostly carpeted) at one time, thus I'm wondering if I could simply (temporarily) roll up the existing carpet, install tubing sort of "embedded" in the padding, then roll the carpet back down?

Probably not--there's probably too much chance of a concentrated load damaging or squeezing shut the tubing, but it's still going to percolate in my mind for a while ;-)

Oooh - I like that idea. The boiler heats the standing radiators and in turn the house, after the boiler shuts off use the new PEX pump to circulate the remaining boiler and radiator heat through the PEX. That's really great advice.

Thanks everyone!

This is a good idea.

I think many people have been and are going to be duped into buying high efficiency condensing boilers when the radiation in their home is not sufficient to support the low return temperatures.

As I understand it, how can exhaust gases add heat to return water that is at a higher temperature than the flue temperature?

My understanding is that flue gases condense at about 130 to 140 degrees F. It isn't the same as with return air temperatures than can be 65 degrees or even less.

The problem is that people, other than gear-heads who read blogs like this, are not usually up to operating and maintaining a sophisticated system. If you doubt me, sell and install a few programmable thermostats.

So, the result is dubious savings to the consumer and the fuel gas supplies, but great gains to installers and manufactures.

3" cooler panels wil drive most of your heat upward, so you should be in good shape there. Just make sure that the ceiling and side walls are well insulated as well. The temperature you will need to heat this room will be minimal and with your zig zag layout any expansion will be readily absorbed. enjoy!

I suggest a couple of changes to your structural design. The thermal expansion of the wood or flooring can cause serious problems to the floor.

First- cut treated 2x4's to match depth of insulation (this provides adequate structural to prevent crushing styrofoam), then install insulation with 2x's between panels- glue both the insulation and boards to basis floor with silicone sealant- just simple strips extruded from a gun.

Second- install 1/2" plywood on a 45 degree bias to the wood "joists" but do not fasten it to the joists- leave 1/4" gap between each panel

Third- install your 3/4" (nominal 1") x 6" coil spacers loosely onto plywood (maybe hold with rolled (adhesive out) aluminum duct tape under boards, and then install your tubing coils.

Fourth- install a second 1/2" plywood sub-floor- tightly connected- on opposite 45 degree bias, with screws going through tubing spacers but NOT into lower 1/2" plywood. Allow 1/4" annular spacing from walls.

Fifth- install your tile floor per manufacture's specs and cover edges at walls with baseboard- overlapping but not attached to flooring.

Sixth- Use a separate pump for the hot water feed to the underfloor system and pipe it with a three-way valve to feed up to 100% of the return water back to the pump inlet (between pump and main hot water header) with other outlet of valve going to return water main to boiler. Use a control system to maintain water in underfloor loop below 120F at peak temperature and use room thermostat to control 3-way valve to maintain room temperature. IF you have heating problems, it would be better to also feed a coil in the supply duct (I assume that you will have A/C to this space) rather than increasing the temperature of the underfloor water- usually, 110F is the peak temp used for these systems.

Depending on how far you want to go, you can also link your cooling system to make 65F MINIMUM cool water for underfloor radiant cooling- using the same control sequence in reverse- cooler water as temperature increases.

energygod - Based on the complexity of this design, I am going to venture to guess that you know exactly what you are doing and this would be the best route to take. I wish I had the money and patience to build the system you have proposed at my house to see if it would work better than my current methods.

Have you ever installed a system like you described? I would be curious what the cost would be.

Part of my suggestion was based on the OPs installation plans. Personally- I would go for just a 3/4" slab of styrofoam on the floor with 1x2 spacers and then generally stay with the sandwich described. If you wanted to go a little cheaper, you could likely only use 1/4" plywood for the lower part but I think you will need the 1/2" for the "true" subfloor below the finished surface.

Running water for hydronic cooling is a good thought, but only if the humidity will accept it. If the OP is anywhere near the midwest USA he will have wet floors unless he can control the dewpoint in the room.

This strategy might work in Arizona, but it is a recipe for disaster in humid climates, especially in a residential setting where the possibility exists for kids opening and closing the doors.

That is why the minimum temperature is 65F- dew point for72F and 50% RH is just over 60F. You need to get up to 78F at 50% RH to approach 65F dew point.

does your garage freeze at night?

Yes, my garage could freeze. I live in Buffalo NY. I won't be doing cooling with this system. The freezing issue has crossed (actually more like a brick) my mind. I am thinking to keep the water pump circulating 24/7 if room temperature fell to 40 degrees F.

Just saying... running cool water through a hydronic floor heating system requires more than just a circulator. It requires dew point control which in our neck of the woods would be an air handler of some sort and a monitoring and control system. It is all doable, but at what expense in a single car garage?

Plus the chance of upsetting the system gets greater if it is an active living area.

A lot of radiant is installed successfully for snowmelt in the frosty climes. As long as you use a glycol water mix you should be just fine. However, this is best kept isolated from the heat source by a heat exchanger. Does this make the effort more complex than you wanted?

I run straight domestic water in my water heat loop. Hmm...should I move to a glycol mix?

Any other benefits than freeze protection?

If you are mixing the water in your heat loops with potable water in any way you run the risk of Legionaire's disease. For example, most people have areas of common plumbing like single spigot faucets that can get contaminated.

Your heat loops sit for months unciculated and all manner of anaerobic nasties can live there.