RADIANT SLAB FLOORING CHOICES - CONTENTS: Radiant heat below wood flooring: what is the suitability of wood flooring compared with ceramic tile for use over radiant-heated concrete slabs. Choices of finish floor materials for concrete floor slabs. Damage to wood floors placed over radiant slab heat systems. Insulating effects of wood vs. ceramic tile over a radiant heat floor slab
Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices
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Choices of flooring types to use over radiant heat:
This article discusses the suitability of various tubing materials for radiant heated concrete floor slabs, and choices of heat conducting fluids for radiant floors. Our page top photo shows part of our investigation of wood flooring gaps over a radiant-heat tubing system installed during new construction of a New York home.
When the owners complained about odors traced to the radiant heat tubing the installer tried to "cook" out the volatiles in the tubing by pushing the radiant heat system temperatures higher than normal. Ensuing flooring dryout and gapping became an issue for the new owner. In the photo, each of our pencils marks a gap in the oak strip flooring.
Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
Our photo at left shows a concrete floor radiant heat system installed in Minneapolis MN in 2009.
The question-and-answer article about wood flooring over a radiant heated slab, quotes-from, updates, and comments an original article, from Solar Age Magazine and written by Steven Bliss.
What are the Effects, Problems, and Benefits of Choosing Finish Wood Flooring Compared with Ceramic Tile Over a Radiant Heated Floor Slab?
I am considering both ceramic tile and wood as finish floorings over a radiant slab similar to those featured in Solar Age (5/82).
The tile flooring would cost three times as much as the wood flooring. Would the heat from the radiant slab dry out, warp, [or cause ugly gaps between the boards of] the wood floor?
Also, how would the insulating effect of the wood affect the radiant slab's performance?
-- Thomas B. McCormick, III, Berkeley, CA.
Dan Lewis of KLR Engineering, Keene NH ran a computer simulation on a 1500 square foot house with 200 square feet of solar collectors supplying a radiant slab floor.
Adding an R-2 carpet and padding to the floor raised the home's auxiliary heating load by 9 percent or about one million BTUs.
A thin wood floor installed with mastic directly to the concrete slab should have even less of a performance penalty.
The 90 degF to 100 degF temperatures of a radiant heated concrete slab won't harm the wood flooring, but you should check on the temperature range of the adhesive.
[Added comments by DJF]
Be careful about wood floor installation moisture and radiant heat slab operating temperatures
At RADIANT HEAT we describe wood floor damage complaints that we have investigated when wood floors were installed over a radiant floor heating system - in each case it appears that the problem was due either to improper floor installation, such as installing a wood floor at a too-high moisture level, or due to operating the heated floor slab at a higher temperature than recommended by the heating system manufacturer. (See our wood floor photo at page top for an example.)
Be careful about about installing a raised wood floor over a radiant heated slab
To avoid possible wood floor damage over a heated slab, some installers prefer to install a floating wood floor that is not secured directly to the slab, often over a "leveling board" that itself has some insulating value, probably increasing the home's heating load as in the model above.
Worse, installing a wood floor nailed to 1x or thicker sleepers (often 2x4's are used) floating over a radiant slab is likely to significantly increase the floor's insulation properties and reduce the effectiveness of the radiant heated floor slab, regardless of whether the heat is from a solar source or from another heating source such as a boiler.
Our OPINION is that ceramic tile will perform trouble-free over a radiant slab floor and in some installations such as our Green Cabin project discussed at RADIANT HEAT FLOOR MISTAKES, solar gain was also possible - of course that wasn't for a basement slab.
Our OPINION is that a wood floor over a radiant heat floor system can also be trouble free provided that the system and the flooring are properly installed. But there are more opportunities for foul-ups.
Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
The link to the original Q&A article in PDF form immediately below was preceded by an expanded/updated online version of this article.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
how will radiant heat over high thermal mass affect the heating system?
(July 5, 2011) Rick K said:
How would installing radiant heating above the insulated conc. slab in a sand bed with brick 'flooring' over the sand bed? This approach would seem to have a lot of thermal mass, but how will that affect the efficiency of the heating system if at all?
Rick I'm not sure I've got a clear picture of the radiant floor design you are discussing. But pertinent may be not just thermal mass but the thermal conductivity between the thermal mass and the heat source and heat destination. Also I'm a little confused about whether we are looking for thermal mass (the concrete slab plus sand plus brick flooring above) vs. radiant heat tubing below a floor.
If we are installing a passive heat system such as passive solar heating in which a brick floor absorbs heat coming through windows, we want good conductivity between the brick surface exposed to sunlight and the concrete slab; I'm not sure sand is adequately conductive (but that's not my expertise);
If we are discussing an active radiant floor heating system we want most of the heat from the heat source tubing to flow up through the brick and into the occupied space; if our radiant tubing is sending heat also down into the insulated slab that system may still work PROVIDED the slab is perfectly well insulated its bottom and sides; what ruined the radiant heat flooring we discuss at
RADIANT HEAT Floor Mistakes to Avoid ( on this page at Continue reading we provide an INDEX to RELATED ARTICLES that includes a live link - ) was that the contractor put the tubing way too deep (2" below floor top surface would have worked, he put it 12-18" deep in concrete) and the fool also refused to fully insulate the slab below. We were sending more heat into the earth than into the room.
Question: least "toxic" radiant heat flooring
8/28/2014 After spending several hours reading online (and my head feeling like it's going to explode from trying to find and comprehend information I don't really understand) I'm hoping I might get an answer here, as this seems like a good informational site. I have a single car garage that I want to use as a workshop room.
My house is in Colorado, so it's very cold in the winter. I'd like to know the best (and LEAST TOXIC) insulation to put on top of the concrete slab, and then put one of those electric radiant floor heat mats down, only about 10 ft X 12 ft section. Then some sort of non-toxic floor on top of that. Everything everything I've read tonight, I'm wondering about Rockwool boards? Any suggestions? Thanks!
I've thought about this interesting question but don't arrive at a trivial, simple answer. "Toxic" to whom, when? is part of the trouble. Some materials may be toxic to the environment or to workers when manufactured but rather inert when purchased and installed.
Other products may outgas only when new.
For ceramic tile, wood floors, engineered wood floors, often the finish floor is going to provide a fairly good seal over what's below it.
And if you under-insulate below the electric radiant floor heat source you risk heating the earth rather than the occupied space.
I like foil faced solid foam insulating boards.
I would check with the manufacturer of the electric radiant heat flooring product for their recommendations.
A thin-set ceramic tile is among the most inert finish floorings you might choose.
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Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years.
ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: email@example.com
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com
Portland Cement Association: www.concretethinker.com/Papers.aspx?DocId=8 indicates that
- tubing for radiant heat in a concrete slab is installed UP TO two inches below the surface of the slab
- the slab is insulated from the ground at all sides to direct heat upwards to the living space [this is our preferred design for a cold northern climate]
The Radiant Panel Association: www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=1 offers design guidelines at http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=115 including these insulation R-value and coverage details:
Application#, Minimum R-Value, and Insulation Coverage
The following insulation alternatives are given for Slab on Grade construction:
Alternate #1 [(Ti-To)x0.125)=R-value, with coverage from perimeter to below frost line ["Ti-To" means we calculate the necessary R-value as (Ratio of indoor to outdoor temperature) x 0.125]
Alternate #2 R-value=5, with coverage 4' horizontal or vertical at perimeter
Alternate #3 R-value=5, with coverage under entire slab and slab edge [this is our preferred design for a cold northern climate]
The Radiant Panel Association offers education and publications in radiant heat design. See radiantpanelassociation.org
Takagi radiant heat systems: Takagi offers pre-assembled radiant heating system installation packages including for do-it-yourself'ers, and including systems that combine radiant heat flooring with domestic hot water production using a gas-fired tankless water heater. See takagi.com for more information. "The T-KJr model (gas inputs up to 140,000 BTU per hour) is the smallest unit in the Takagi line-up. The T-KJr is perfect for light residential (i.e. small apartment units) and radiant heating applications." Also see Tankless Water Heaters.
Passive Solar Design Handbook Volume I, the Passive Solar Handbook Introduction to Passive Solar Concepts, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v1.pdf
Passive Solar Design Handbook Volume II, the Passive Solar Handbook Comprehensive Planning Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v2.pdf [This is a large PDF file that can take a while to load]
Passive Solar Handbook Volume III, the Passive Solar Handbook Programming Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v3.pdf
"Passive Solar Home Design", U.S. Department of Energy, describes using a home's windows, walls, and floors to collect and store solar energy for winter heating and also rejecting solar heat in warm weather.
"Solar Water Heaters", U.S. Department of Energy article on solar domestic water heaters to generate domestic hot water in buildings, explains how solar water heaters work. Solar heat for swimming pools is also discussed.
"Heat-Transfer Fluids for Solar Water Heating Systems", U.S. DOE, describes the types of fluids selected to transfer heat between the solar collector and the hot water in storage tanks in a building. These include air, water, water with glycol antifreeze mixtures (needed when using solar hot water systems in freezing climates), hydrocarbon oils, and refrigerants or silicones for heat transfer.
"Solar Water Heating System Freeze Protection", U.S. DOE,using antifreeze mixture in solar water heaters (or other freeze-resistant heat transfer fluids), as well as piping to permit draining the solar collector and piping system.
"Solar Air Heating" U.S. DOE also referred to as "Ventilation Preheating" in which solar systems use air for absorbing and transferring solar energy or heat to a building
"Solar Liquid Heating" U.S. DOE, systems using liquid (typically water) in flat plate solar collectors to collect solar energy in the form of heat for transfer into a building for space heating or hot water heating. The term "solar liquid" is used for accuracy, rather than "solar water" because the water may contain an antifreeze or other chemicals.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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