PEX Tubing for Radiant Heat

If by standard you mean a closed system, with cast iron pumps, valves and a boiler, then oxygen barrier PEX is the right tubing for you. Brands of oxygen barrier PEX include hePEX, MrPEX, HydroPEX, and Viega PEX.

Wirsbo hePEX and MrPEX tubing are both PEX-a products. PEX-a uses is made using the best manufacturing process (the Engel method) and produces the strongest, most flexible tubing. PEX-a tubing is also the only tubing that can be used with expander style fittings. hePEX is more expensive than ThermaPEX because it is made by Wirsbo (Uponor), the leading brand name, who have been the world leader in PEX for decades. The other brands of PEX, HydroPEX and Viega PEX, are comparable and can be used in standard radiant applications. All of these brands carry at least a 20 year warranty.

There are many different ways to install PEX tubing in a radiant heat system. The most popular are in a slab, in joist bays with aluminum panels or PEX clips, or in a Quik Trak above subfloor system. The most efficient and least expensive way to install PEX is an in-slab application; but unfortunately this option is not always available.

1/2" is by far the most common size of tubing used in radiant heat. 5/8", 3/8", and 3/4" follow behind. The size of PEX tubing used does not change the amount of heat that is produced, but it does change the maximum loop length that can be run.

The spacing of PEX tubing in a radiant heat system determines how much heat a given area will produce. This spacing or distance between two PEX lines is also referred to as the on-center distance. The closer that tubing is spaced, the higher the BTU output will be, given that water temperature is held constant. When laying out your tubing you must keep this in mind. For basements and shops, 12" spacing will work. For living areas, tubing can be spaced roughly 9" apart. For a bathroom, tubing can be 6-7" apart. This spacing assumes a moderate climate; if you are located in a warm climate tubing can be spaced farther apart and if you are located in an extremely cold climate tubing should be spaced closer together. Along exposed walls, tubing should be spaced 6" apart for the first 2-3' to combat the heat loss.

For baseboard and other hydronic heating applications you will want to use either oxygen barrier PEX or PEX-AL-PEX tubing (the aluminum core acts an oxygen barrier). In most applications oxygen barrier PEX (such as MrPEX or hePEX) will be used. However, PEX-AL-PEX, because of its ability to hold its shape, is often used. Both of these products are able to withstand temperatures up to 200° F. The oxygen barrier will prevent rusting of cast iron components in your system.

PEX-AL-PEX tubing is used in some slab applications, Warmboard applications, and in some hydronic heating jobs. The main advantage of using PEX-AL-PEX is its ability to hold its shape when bent or pushed a certain way. This can be great in tight situations such as in the boiler room and for baseboard. However, for in slab and joist applications this tubing can be difficult to work with. PEX-AL-PEX can is great for high temperature systems as well because it has a very low expansion rate of .156" per 100 feet for a 10° temperature rise.

No, you cannot use PEX on a solar system because the water temperatures in a solar system can reach 325°, which is too high for PEX.

PEX (cross-linked polyethylene) tubing is a flexible pipe used in radiant heat and hydronic heating systems. Radiant heat is growing in popularity, and is now the preferred heating system in new homes. Radiant heat provides more comfort throughout the home than standard baseboard heat. PEX tubing is installed beneath the floor and heats the home from the ground up. As the floor becomes warm, the room is heated evenly and efficiently. Radiant heat is silent, producing no creaking, banging, or humming sounds that are commonly heard in other heating systems. Radiant heat allows you to turn the thermostat a few degrees lower than you normally would while providing the same warmth. This cuts energy bills and saves you money.

PEX tubing is approved by all major plumbing/heating codes and bends easily, making it more versatile than standard copper tubing. Manufacturers of PEX generally provide a 20-25 year warranty, but PEX is known to have a much longer lifespan. 1/2" PEX is the most common size used in radiant heat, but 3/8", 5/8", and 3/4" are also available.

Types of Radiant Heat Tubing

Oxygen Barrier PEX
The "barrier" referred to in PEX tubing is an oxygen barrier. The oxygen barrier assures that no oxygen will enter the heating system. A standard radiant heat system is a closed system that includes cast iron pumps, valves, and a boiler. This type of system requires an oxygen barrier PEX to prevent the cast iron components from rusting over time. If oxygen barrier tubing is not used, components in the system should be brass, bronze, or stainless steel which are more expensive. We offer several types of oxygen barrier PEX including Uponor (Wirsbo) hePEX, ThermaPEX , Bluefin, and Viega PEX.

PEX-AL-PEX
PEX-AL-PEX (PEX-Aluminum-PEX) is a three-layer oxygen barrier PEX Tubing. The main benefit of PEX-AL-PEX is that it maintains its shape when bent. While traditional PEX is flexible, it returns to its original shape when left unsecure. Once bent, PEX-AL-PEX will hold that shape until bent again. PEX-AL-PEX has less expansion capacity than standard PEX. PEX-AL-PEX is generally used in outdoor heating applications, warmboard systems, and high temperature systems such as baseboard or fan coils.