Eight inches on center for 1/2" PEX per page 18, paragraph two of this Design and Installation Manual.

Does it not matter on the thickness of the slab and also the amount the pex is "buried?"

The first thing to determine is the temperature of the fluid you will be using to circulate within the tubing. Temperature will determine the spacing. Four inches of insulation would be even better particularly in a cold climate.

The lower the design temperature of the fluid the greater the efficency of the whole system particularly if the heat source is a heat pump. Thickness of the slab and depth of the tubing also matter with regards to thermal response and heat retention.

This is NOT a DIY design project!

IMPO

SR

Thanks for the info wdccruise

Stax my slab will be 4” the lines will sit roughy 1-2” in the concrete

fsq4cw ill be using glycol. I appreciate the info. The manifold and electric boiler will be done by a professional. But once i figure out the spacing, laying the line will be relatively easy as long as i keep my runs 250’

By mixing contractor and home owner responsibilities, this project has the potential for finger pointing and worse in the event of a problem. The bulk of the cost is in the equipment and piping--not the labor component-- so DIY won't generate a substantial savings. I suggest you contract with a single source responsible for the design, installation, and guaranteed performance of the system since mistakes will be, well, cast in concrete.

There are a number of manufacturers of tubing designed for hydronic radiant heating systems. Some offer various products for spacing tubing, emitters, etc. and have specific instructions for how their tubing is to be installed. The installer should follow the specific manufacturer's instructions.

A hydronic radiant heating system is just that--a system. It's important that components and sub-systems are compatible and installed properly. To that end, I recommend a single source for design and installation of the complete system so there's no finger pointing if it doesn't perform as designed.

I would just ask the professional that is doing the boiler and manifold how he would like it to be done.

If and when there's a leak in the tubing, it's not the boiler/manifold installer's responsibility; it's on the home owner. So the homeowner assumes a level of risk to save a relatively small percentage of the total installed cost of their hydronic radiant heating system. In my view it's not worth it.

@Charles Ross Homes Oh, I'm in compete agreement with you. I would never consider this to be the spot to save a couple of bucks.

Horror story to follow. We were doing a renovation. The house already had hot water radiators. We wanted in floor heating in the kitchen due to space constraints and not wanting a radiator to take up space.

We hired plumbing contactor to do the job. He used a spacing material on the floor that had channels for the piping to be snapped into place. This kept the spacing in the proper size. Upon completion, Advantech flooring was carefully placed on top per instructions of manufacturer. A slate tile floor was planned for the final surface.

Our carpenter got to talking instead of paying attention to what he was doing. Typical for this guy. Anyhow, he hit the piping square with his nail gun. I thought we were going to have to tear out the whole installation and start over. Fortunately there was a piping patch kit could be used and only required removal of the affected panel of Advantech. We had a weeks delay waiting for the specialized couplers and kit.

We had been so careful to do this the right way. I could have easily killed the carpenter with his own nail gun. Hire a professional and watch them like a hawk.

That looks like what we used. The underside of the channeled panels was foiled to reflect the heat upwards. We were NOT installing in a concrete pad.

mtvhike we plan on having it just in the basement do you by chance know how far apart the lines were spaced?

Jeff, here are some photos of the basement lines:

In this picture, you can see the lines coming up along the wall; they are 4-1/2 inches apart.

In this picture, you can see the steel network of heavy wires placed before the radiant tubes were installed.

Mtvhike, thanks for the answers. What are your winter temperatures like outside?

No lower than -20; usually +10 (minimum, at night). I'm in upstate NY, near Burlington, VT.