Reduce your environmental footprint one strategy at a time.

Radiant Floors

Posted on | June 19, 2009 | 2 Comments


Radiant Heating diagram courtesy of This Old House

Radiant flooring (also called warm floors or underfloor heating) is a method of providing heat via a series of tubes that carry hot water and are installed just below the surface of the floor.   The Romans used this technology in their baths 2000 years ago by heating fires below their stone floors.

The main benefit of radiant flooring is how comfortable and consistent the heat is.

Heat rises…so the heat in the floor is delivered directly to where the occupants are.  Unlike with a forced air system, there is less energy wasted warming up the ambient air in order to keep the occupants comfortable and no filters to change or allergens blowing around.  And unlike with a steam heating system, there are no knocking noises or potential for burns from steam radiators. Reply from Genarro:  You say in your post that heat rises. It doesn’t. Hot air is lighter than cold air but that is a function of air displacement and gravity.  Actual heat moves any which way from hot to cold. The reason radiant heating is so great is that the heat radiates, which is one of the ways heat can move through space. (With apologies to my Science Teachers – I forgot about the first law of thermodynamics!)

At the top of this post is a diagram from This Old House showing how a typical radiant heating system works.   A boiler sends hot water (not steam) through a series of tubes fastened below the finished flooring.  The warmth from the hot water in the tubes radiates upwards and is transferred directly to the space above.  

As with all sustainable strategies, this one is not appropriate for every building.  We have had successful results installing radiant heating below solid wood flooring, engineered wood flooring and bamboo floors.  However, if you can install radiant flooring below or embedded in a tile or concrete floor  you will have a even better result because the mass of the masonry holds the heat and releases it slowly.

I toured a green brownstone under construction at 22 2nd Street in Carroll Gardens, Brooklyn, being built by Gennaro Brooks-Church of Eco Brooklyn.  It has many interesting green features but it was the radiant heating that caught my eye due to some innovative adjustments which I’ll describe below.


Picture #1: Warmboard subflooring

Picture #1 shows installation of the tubing in a Warmboard subfloor.  Warmboard is a combination structural subfloor and radiant heating system.  Genarro basically made his own Warmboard subfloor with plywood but wrapped the plywood cutouts in sheet aluminum to help radiate the heat upwards and filled in all the gaps between the tubing and the plywood with concrete to add thermal mass as well as reduce the amount of air in the floor (air is a terrible conductor of heat)


Picture #2: Homemade Warmboard with aluminum and concrete.

Other innovations at EcoBrooklyn: encasing the underside of the entire structural bay in concrete to add thermal mass to the design (Picture #3).  Genarro said that was very time intensive so he tried to focus the encasement of just the tubing in concrete for added insulation and thermal mass (Picture #4).


Picture #3: Encasing the structural bay in concrete


Picture #4: Encasing tubing in concrete

Picture #5 shows the manifold connection to and from the boiler in the Cellar.


Picture #5: Manifold to/from boiler

We’ll check in with Genarro later in the project to see how this system is holding up.


2 Responses to “Radiant Floors”

  1. Mary
    June 23rd, 2009 @ 11:01 pm

    Pretty good post. I just stumbled upon your blog and wanted to say
    that I have really enjoyed reading your posts. Any way
    I’ll be subscribing to your feed and I hope you write again soon!

  2. Debra Salomon
    June 29th, 2009 @ 4:47 pm

    Great post on radiant flooring.
    Kudos on the blog!
    Really good information and down to earth writing.I’ll follow with interest.

    Debra Salomon


Established in 1999, Ellen Honigstock Architect PC is a full-service architecture and energy auditing firm based in DUMBO, Brooklyn.

Our solutions are environmentally conscious and the criteria we use are based on national standards developed to bring long-term saving, efficiency and well-being to our clients. Over 35 years combined experience building in New York City gives us an edge in meeting tough schedules and navigating the city's complicated requirements.

About Ellen:

As the Residential Green Building Advocate for the Urban Green Council since 2007, Ellen has been promoting sustainability in the residential marketplace in NYC.

In the position of Chair of the Homes Subcommittee the NYC Greening the Codes Task Force, Ellen has been heavily involved in recommending new green policy in NYC as related to updating building codes, rules and regulations.

Ellen teaches Building Science, Building Envelope, Water Conservation, Indoor Air Quality, Quantifying Energy and Green Building Plans at the 1,000 Green Supers program for The SEIU Local 32 BJ Thomas Shortman Training Fund.

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Ellen Honigstock Architect PC
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