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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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Readers should also see RADIANT HEAT where we describe radiant heat damage to wood floors, and see and RADIANT HEAT Floor Mistakes to Avoid, as well as SLAB INSULATION, PASSIVE SOLAR.
Our photo at left shows a concrete floor radiant heat system installed in Minneapolis MN in 2009.
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 to Avoid, 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.
See these articles on radiant heated floors
FLOOR, WOOD RADIANT HEAT - guide to installing wood floors over radiant heat systems - this article is provided just below
Also see Thin Film Radiant Heating Systems for Ceilings & Floors for examples of how electric radiant heat may be installed beneath several types of finish flooring.
The link to the original Q&A article in PDF form immediately below was preceded by an expanded/updated online version of this article.
Frequently Asked Questions (FAQs) about radiant heat in concrete slab floors
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