Hydronic heating and cooling systems utilize heated or chilled fluid, usually water and sometimes antifreeze, as a heat-transfer medium which is distributed throughout a building for the purpose of space heating and cooling. Other types of hydronic energy transfer are also related to this scope of work.

Introduction

Hydronic heating and cooling is a 100-plus-year-old technology that is constantly evolving, and hydronic distribution piping is one of the primary applications for the plastic piping materials represented by PPI's Building & Construction Division since its founding.

The hydronic piping materials produced by PPI members provide economical, safe, sustainable, and reliable piping systems for the transport of heated and chilled water, without the cost, corrosion, or environmental issues associated with traditional metal materials, such as copper and steel. Several of these materials (e.g., CPVC, PEX) have been used in hydronic applications for more than 50 years.

Plastic piping materials have been approved for hydronics in model mechanical codes across USA and Canada, including the Uniform Mechanical Code (UMC), International Mechanical Code (IMC), the International Residential Code – Mechanical (IRC-M), CSA B214 (Installation Code for Hydronic Heating Systems), and others.

Note: Plastic piping materials are not approved or intended for steam applications.

Materials

Many of the plastic piping materials represented by PPI's Building & Construction Division are intended and certified for hydronic distribution piping. This includes certain CPVC, HDPE, PEX, PEX-AL-PEX, PE-RT and PP pipe and tubing materials, as well as the fittings which are designed for use with each of these piping materials. Within radiant surface heating/cooling systems, PEX, PE-RT and PEX-AL-PEX materials are most commonly used. Due to the long lengths, and large surface area of tubing used in radiant systems, some PEX and PE-RT tubing materials are available with co-extruded oxygen diffusion barrier layers which practically eliminate the transmission of oxygen from the atmosphere through the tubing wall. This is intended to prevent oxygen from dissolving into the hydronic fluid and potentially causing corrosion in any ferrous (i.e., iron or steel) components within the piping system. The aluminum core layer within PEX-AL-PEX tubing also serves as an oxygen barrier. Several codes require the use of oxygen barrier tubing in radiant heating and cooling systems.

Please read more about each of these piping materials, including the specific product standards to which they are produced, on the webpages for each of the materials.

Note: Be sure to follow the pressure/temperature ratings for each piping material in every application. HDPE piping is not recommended for hot water applications. 

Applications

Hydronic heating and cooling systems use a variety of heat emitters to transfer thermal energy to or from a space. Common examples include fan coils, convectors, radiators and chilled beams. This also includes radiant surfaces, sometimes called radiant panels, which use embedded tubing within floors, walls, or ceilings.

Hydronic piping systems are used in practically every type of residential, commercial, institutional, and industrial buildings.

Advantages of Plastic Piping Materials

Plastic pipes do not erode or corrode, preventing expensive damage that can occur when metallic pipes leak. Plastic pipes also do not experience scale build-up, which can impede flows, increase pumping costs, and reduce system efficiency.

Flexible plastic pipes such as HDPE, PEX, PEX-AL-PEX, and PE-RT are avalable in long coils in excess of 1,000 ft (305 m) and allow for bends and sweeps to be formed by hand, reducing installation time and pressure loss in the piping. When needed, a variety of reliable and easy to use fittings systems are available for these materials.

CPVC pipe is typically joined to fittings using solvent cement which chemically fuses the components into a monolithic piping system. PP pipes and fittings are typically joined using heat fusion which physically welds the components into a monolithic piping system. Mechanical compression fittings are available for each of these piping materials. These proven joining techniques eliminate the use of flame for constructing the piping system.

Since these plastic materials are inherent insulators, thermal heat transfer through the pipe wall is reduced, an important factor when transferring heated or chilled water over long distances throughout buildings.

Sustainability

In addition to the inherent advantages listed above, plastic piping systems are sustainable choices for numerous reasons:

• No mining operations are utilized to extract ore, as with metals
• Much lower net energy cost to produce plastic as compared with metal pipes
• Smooth wall, excellent flow characteristics reduce pumping costs
• Flexibility can dampen pressure surges and water hammer, reducing pressure spikes and extending equipment life
• Plastic materials do not support biofilm growth, reducing the need for water treatment chemicals such as corrosion inhibitors
• Their light weight reduces transportation energy usage and costs
• Many plastic piping materials are recyclable after their service life is complete

To summarize, plastic piping systems used in hydronic heating and cooling systems protect health, safety, and welfare!