A radiant floor heating system can be used with a couple different sources of heat sources.  The most popular is a hydronic source running off of a boiler but the most sustainable is a geothermal heat pump.  However, the application of a radiant floor heating system is debated as a sustainable heating option.  It has been experimented in with commercial and residential buildings, also in cold, moderate and warm climates.  The most popular debate is based on its use as retrofit system or in new construction.

Radiant floor heating systems are installed under subflooring and floor finishes such as hardwood or tile.  It is completely hidden, consisting of tubes embedded in a concrete or gypsum slab.  The tubes are filled with water or gas as necessary that is supplied by the heating source.  The space above the floor is heated by radiation and also convection through the floor.  An equivalent level of comfort can be achieved compared to air induced heat by setting the thermostat 4-8 degrees cooler. 

At first glance this may seem like a sustainable energy efficient system for moderate to cold climates.  However, it is not appropriate for many green homes because it contradicts and interferes with other systems and technologies.  A highly insulated home designed for energy efficiency would become too hot with a radiant floor system.  A person’s feet could heat up the slab through convection to warm up the room.  Also, any passive solar design could warm up the space additionally as well.  So in the case of a home demanding low heating loads, a radiant floor heating system can be considered over-engineered.  

Economically, the use of radiant floor systems may be more of an expense than needed.  The sources required to heat the system are expensive to install.  This is an unnecessary expense considering heating bills that only cost a few hundred dollars a year. 

So what about using a radiant floor system for an energy retrofit?  There are several aspects to consider when deciding to retrofit a home for sustainability and energy efficiency.    Will you upgrade the building envelope, energy systems, or a little bit of both.  This varies from home to home depending on location and existing circumstances.  One should have an energy audit completed on their home to determine specifics. 

The use of a radiant floor heating system can be a wise decision for many homes that see a fair balance of all four seasons and are not designed with highly efficient building envelopes.  Goals in a sustainable home retrofit should eliminate air leaks in the home such as walls, roofs, windows and doors.  If considering investing in radiant floor heating, it makes the most sense economically to fix the larger air leaks without investing too much money on completely new insulation or EIFS systems.  Finding a fair balance of minimal building envelope upgrades and a radiant floor heating system will provide optimal sustainable return on investment.