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Applying the radiant heating


Radiant Hydronic Heating Systems

The Problem:

Heating systems that distribute heat to the living spaces with hot water are powered by boilers. A fairly recent development in residential applications has been the "radiant floor" system where the "hot" water is circulated through pipes in the floor.

There have been many problems with these systems mostly due to improper installations, corrosion problems and failure of the plastic pipes.


Boilers usually heat water to approximately 180° Fahrenheit (82° Centigrade). The water inside the boiler is contained in the "heat exchanger". Older boilers with heavy cast iron heat exchangers for conventional applications tend to last 30 - 50 years in service. Most newer, lighter boilers use steel or cast iron, and some use copper. The new boilers have life expectancies of 20 - 25 years with few manufacturers offering warranties exceeding 10 years. Under adverse conditions often encountered in radiant slab systems, boilers have been known to fail in less than 10 years.

Boiler Installation

The boiler must be installed so the internal operating temperature stays above 140°F (60°C) to avoid internal condensation and corrosion. The boiler piping must installed to provide tempered water to the floor panels typically within the temperature range of 110°F - 120°F (40°C - 50°C) so the floors do not overheat and the plastic pipes do not break down.

In the picture above, one of the problems is that the boiler piping incorrectly mixes the cooler floor panel return water with the boiler's own hot recirculating water. This is a common mistake and prevents the mixing value from operating properly.


The piping used in almost all "radiant slab" hydronic systems in the Metro Vancouver area is plastic.

In the 1980s and 1990s, grey polybutylene piping rated for potable water applications was most commonly used. It had two major deficiencies:

The first improvement in the piping was the addition of an "air barrier" coating on the outside of the pipes to reduce (but not eliminate) air penetration.

This was followed by a change to the use of cross-linked polyethylene ("PEX") pipes with various air-barrier technologies. PEX is suppose to be a more stable plastic than the polybutylene but in general, these pipes still allow air penetration and are not recommended on systems operating at temperatures above 140°F (60°C).

The Risks:

The risks of owning a "radiant hydronic heating" system appear to be as follows:

Last updated October 24, 2010

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