What is it that makes radiant heat so intimidating and potentially trouble-prone? It can be summed up in one word: moisture. Even without radiant heat, moisture is probably the leading cause of wood flooring callbacks. Add radiant heat, and the potential for moisture problems is greatly increased, because radiant heat dramatically exacerbates moisture fluctuations in a wood floor. To understand that, it helps to know a little bit about how radiant heat systems work.
The concept is familiar: The heat we feel from the sun or from a crackling fireplace is radiant heat. Radiant energy travels through a space without heating the space itself unlike a typical forced-air heating system, which actually warms the air.
When radiant heat comes across a cooler surface like a human being , it attempts to equalize the temperature difference, giving off its heat. Most radiant heat systems used in the United States today are hydronic, meaning the subfloor has plastic tubes through which hot water flows. The water may be heated by anything from natural gas to electricity to solar energy. The tubes may be embedded in a slab, inside a cementitious material between sleepers, stapled to the underside of a wood subfloor, run inside the grooves of a prefab subfloor panel, or installed using any number of other techniques see the "Many Options" sidebar on page The technique used is the main factor in how hot the water has to be to create the required heat for example, a concrete slab conducts heat well and therefore needs a lower water temperature than a system with tubes suspended in the empty space between joists.
There are also electrical systems available that involve large electrically heated mats, although these are much less common. A radiant heat system heats all the materials around it, in the process drying everything, as well. It drives moisture from the joists, the slab, the subfloor—and the flooring.
Contractors who have vast experience with radiant heat caution that it is not the type of job for a novice wood flooring installer. There are too many variables: the knowledge of the general contractor, radiant heat installer, plumber and electrician; the region's and home's anticipated moisture swings; the type of radiant heat system; other HVAC equipment that may be installed; and the type of wood flooring, to name a few.
One contractor even compares radiant heat jobs to defusing a bomb—safe if you know exactly what you are doing, explosive if you don't. Wood flooring contractors who typically get away with not playing by the moisture rules will find their luck has run out when they attempt to do a radiant-heated floor.
Before taking on a radiant heat job, you should feel comfortable with everyone involved. The GC should be open to learning everything you can teach him about wood flooring and moisture, and, as best you can tell, you should feel that the radiant heat installer, HVAC contractor, plumber and electrician are all competent and know what they're doing, not experimenting with their first radiant heat job.
You'll also need to know exactly what kind of HVAC systems will be installed. By code, radiant-heated homes must have some kind of ventilation system, and they are often supplemented with a typical forced-air system that includes air conditioning. There should also be systems in place to help stabilize humidity year-round. All of this, along with knowledge of your area, will help you predict what kind of moisture swings the floor will experience.
If you think the swings will be substantial and that humidity control won't be a priority, it's probably a good idea to walk away. If you feel the job site will be manageable, it's still critical to educate everyone involved, especially the homeowners, about wood flooring expansion and contraction, and why they need to control the humidity levels in their home.
There are no guarantees, but there are product choices you can make to increase your chances of an acceptable wood floor over radiant heat. Some good options:. Tangential shrinkage values see the NWFA's Technical Manual A Wood Species Used in Wood Flooring give an indication of stability as found in the lab, but many wood flooring contractors have found the species perform differently on real job sites.
Walnut, cherry and oak are examples of relatively stable species; beech, Australian cypress and many bamboo products are examples of those that are not. Engineered floors including floating floors are more stable, but keep in mind that they are not bulletproof. No matter which type of product you choose, make sure it's from a reputable manufacturer.
A radiant-heated floor is no place to gamble with an unknown product. Exotics can be particularly susceptible to problems resulting from bad drying practices, making a reliable manufacturer even more crucial.
A strange phenomenon that can happen with radiant heated floors is color change directly over the tubes. This typically happens with oily woods, including many exotics, such as rosewood or teak. Over the years, the difference in heat exposure directly over the tubes compared with the rest of the floor causes a color change in the warmer areas, which usually turn darker, revealing the exact pattern of the tubes. This is a change that cannot be sanded out of the floor.
Your subfloor will depend on the radiant heat system. If tubes are stapled or suspended under a typical wood flooring joist, a standard plywood subfloor will be in place. A newer system is radiant heat subfloor panels that have grooves for the tubing. Flooring can be nailed directly to the panels, although the flooring direction has to run perpendicular to the tubing to prevent the possibility of a row of fasteners falling directly over the tubing. It also may be helpful to include crack isolation membrane material under the the new thindet tile floor.
Our relative has a house with radiant floor. Do not the type of radiant floor. He thinks he can add another floor over it. Is this possible or advisable? What kind of grout should be used with 18' porcelain tiles over hydronic radient heat floor?
The former grout has dried out. Should silicone be added? Stu If you build a wood framed, insulated floor atop an existing radiant heated slab, you will not get heat up through the new floor unless you also abandon the existing radiant heat system and install a new radiant heat tubing system under your raised floor.
We currently have radiant heat in our home and wish to raise the floor in the sunken step down 18" living room.
The room is 17 x 22' with 12' ceiling. The living room floor is concrete and we have had no problems with the heating the room in the cooler southwestern months. I could use some advice on the joist and type wood to use, if "any" insulation is necessary, subfloor or decking and options for floor covering, wood, ceramic tile or carpet. My concern is making sure the radiant heating system is still able to heat the raised living floor even if the system is not as efficient.
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Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery.
That way they can slowly turn on the radiant heat system as the temperature gradually falls. Also, talk to your customers about installing a humidifier either to add or remove humidity. During the installation process one of the most important steps to take is to turn on the radiant heat system weeks prior to the delivery of the wood. This step will help drive out any moisture present in the subfloor. It will also show if there is any problem with the radiant heat system itself like a water leak.
This step should not be avoided regardless of the time of year. Another key step during installation is to measure the surface temperature of the sub floor and the hardwood floor.
The surface temperature of the sub floor should never exceed 85F. If the surface temperature exceeds 85F, the wood may dry out more than it should and this can cause cracks. Making sure your subfloor moisture readings are on point is of the utmost importance. Take frequent readings of the subfloor before the installation and delivery of the hardwood floor.
You should take readings in all parts of the subfloor. Some radiant heat systems use a combination of gyp-crete and wood sleepers. Know the moisture content of each of these components and be certain they are within spec before the hardwood floor installation begins. The range of acceptable wood floor moisture content will vary according to your specific location.
A floor in New York has an acceptable moisture content that is different from a hardwood floor in Florida. Guide the homeowner in selecting a hardwood floor that is appropriate for their scenario.
One of the best options over radiant heat is to use an engineered hardwood floor.
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