Radiant Floor Heating Guide

There is nothing like the feel of radiant floors. The most comfortable form of heating. It puts the warmth where you want it, under your feet; you can even lower the thermostat and still feel comfortable. But it isn't perfect.

What is Radiant Heating?

Tubing laid out under the floor, connected to a source of hot water, either from a ground source heat pump system, a small gas furnace, or a solar thermal hot water system.

Traditionally the tubing was laid in cement or gypsum concrete (Gypcrete), but now systems are offered where the tubing runs in plastic or foam holders that manufacturers claim can be installed in wood framing without concrete.

Engineers lay the tubing out in complicated patterns to ensure that the heat is evenly distributed; they often pack the tubes more closely together under windows and near exterior walls. The layouts are beautiful things to look at!

Electric radiant systems are also available, but because of the cost of electricity they are usually limited to bathroom floors.

Why we like it

When cast in concrete, the floor acts as a thermal mass that holds the heat for a long time; combined with careful design of south facing windows, it becomes a passive solar system as well.

Because the heat is underfoot it feels warmer, so people set the thermostat lower and save energy. It doesn't heat the air like conventional systems, but heats the people in it.

What we worry about

Systems without cement. Because casting tubing in concrete is very expensive, vendors are selling all kinds of different systems to hold the pipes in place with wood floors. But wood does not conduct heat well, and has little thermal mass to store it; it is like wrapping the pipes in insulation. Then the vendors insist that you can put wood flooring or carpet on top; this just adds more insulation. Not only that, the wood floor will warp. The manufacturers will guarantee that an engineered floor won't; on one job I worked on, the guaranteed floor had to be ripped out after one season.

Almost all of the benefits or radiant floor heating are lost when you put it under wood; there is no thermal mass to store the heat, it is wrapped in an insulating material that doesn't like being constantly heated. Generally, we cannot recommend it.

Thermal Lag
It takes a very long time to change temperatures; because of the thermal mass of the concrete (or the time it takes for wood to transmit heat) turning up the thermostat in the evening when the sun goes down makes little difference in less than a few hours. I was told by an architect who specializes in very green homes that use a combination of radiant heated floors and passive solar that he adds a wood stove to the mix, recognizing that the floors just don't respond quickly.

Maintenance

When your heating system is buried in the floor it is pretty hard to fix. In the 80s and 90s Goodyear sold 25 million feet of Entran II piping for radiant floors; it failed catastrophically, leading to a class action lawsuit that cost Goodyear $ 300 million. But what do you do then? It is impossible to replace. Now the flooring installers use PEX tubing made from high density polyethylene, which is warranted for twenty-five years. Unless your installer left it lying around in the sun for as little as a month; it degrades rapidly.

Air quality
Salesmen will claim that air quality is better with a radiant floor because dust and allergens are not circulated by moving air. This is probably true, but ducted systems can be easily and inexpensively connected to heat recovery ventilators that bring fresh air into the home. Any new tightly sealed home with radiant heat should still have a duct system connected to an HRV.

Eco-factor of Radiant Heating

Most heating systems heat the air in the room, which moves the heat by convection, or air currents. This moves a lot of dust and particles around and a lot of heat gets stuck up near the ceiling. Radiant heat warms by radiation and conduction, and is much warmer at the floor than the ceiling. This takes l

ess energy; you feel warmer and more comfortable and keep the thermostat lower.

Cost of Radiant Heating

A radiant hot water system could cost between 8 and 12 bucks a square foot not including the furnace. Most I have seen have instant hot water heater type furnaces that cost about $ 5,000. The system should be designed by a licenced and experienced engineer and should be zoned appropriately, adding more costs. You should only use experienced and established trades who inspect the system annually. As they say at a Canadian government website, "This is not a do-it-yourself project."

Learn More:

Green Materials: Flooring Guide Step Up to Radiant Floor Heating Consider Radiant Heat : Planet Green Floor Panel Integrated Radiant Heating System By GCS Radiant In Amherst NY