Floor Types and Hydronic Heating
Radiant heat systems are compatible with any type of floor. Generally speaking exposed surfaces such as ceramic tile or finished concrete are the most effective flooring as they are the most conductive. Hardwoods are also effective. Additionally, carpets, vinyl, laminates etc. can be used with good results.
It is important to remember to inform the installer of the type of floor that will be going down and how it is constructed in advance of the job so he can make the necessary alterations as installation techniques will vary depending on the type of flooring used.
Hydronic Heating on Hardwood Floors
To dispel a popular myth; radiant heat can be used effectively underneath hardwood floors. However, when using a hydronic heating system underneath hardwood it is important that extra time and care is taken during the installation process. Wood reacts to water; the term for this is hydroscopic. What this means is that when wood comes into contact with water it will absorb moisture and as a result may expand. Alternatively, it is possible to also install a wood that is too wet in an environment which is too dry, this can result in the wood drying and shrinking or contracting.
As one radiant heating website describes, wooden floors can be very much like wooden doors in that;
‘Wood floors continuously move, just like the door jams in your home. In the summer they expand due to the increased humidity in the air and become harder to shut. And, in the winter when the humidity is typically lower, the doors contract, becoming easier to close.’
These variances are going to occur despite the best efforts of the installer; however there are ways to minimize these discrepancies, the main ones being;
The wood used should be kiln dried. The reason behind this is to ensure that the moisture content of the wood is the same both inside and out. This moisture content should be around 7%-10% and may require an acclimation period. If possible try to ensure that the hardwood floor and the subfloor have similar moisture content. This allows them to expand and contract in unison.
Also an installer should always try to use a strip of wood no wider than 3.5” as narrower planks tend to move less and to further keep the wood in check. It is better to use quarter-sawn wood rather than plane-sawn wood. This is because plain-sawn wood has a tendency to gain width whereas quarter-sawn wood tends to expand in thickness, making it harder to view cracks and gaps with the naked eye.
For those who think they must choose between a luxurious grade of carpeting and radiant heating, think again. While it is true that carpet thickness can affect radiant heat conductivity, if you choose the radiant assembly based on its overall conductivity then your carpet choice will complement it. Radiant heating systems manufactured from thick, highly conductive aluminium should give off the heat required, when using moderate supply water temperatures. In addition, most homeowners are willing to accept some reduction in heating efficiency so that they can enjoy the additional benefits of a plush carpet. However, this efficiency can be improved by selecting the proper carpet padding.
Most experts agree that the slab foam rubber pad is the best choice when it comes to carpet pads. The 3/8” 90 oz. slab foam rubber pad is sold for about $4 per yard where the less costly, lower quality 3/8” 6 lb. re-bond pad can be purchased for approx. $3 per yard. Regardless of cost, slab foam rubber is more popular because most customers who have opted for the luxury of hydronic heating are willing to pay a little more for the carpet pad.
Slab foam rubber pads may be more difficult to find than the more common re-bond pads but are well worth the extra effort. An enthusiast at the Radiant Panel Association (RPA) message board kindly provided these links to related websites; If you contact the two US manufacturers of slab foam rubber pads they will direct you to local distributors:
Sponge Cushion, Inc.
FXI - Foam Manufacturer
Carpet And Heated Floor
The Carpet and Rug institute commissioned a study on Carpet and Heated Floors. Although the study dealt solely with hydronic heating, the findings are also applicable to Electric Radiant Floor Heating.
Hydronic radiant floor manufacturers recommend that total R-value not exceed 4.0. This limitation includes the carpet pad that often reduces the heating efficacy of Hydronic systems.
An industry sponsored carpet thermal study by the Georgia Institute of Technology found that R value was related more to the actual thickness of the carpet than to the carpet fiber itself. An estimated R-value for carpet was calculated to be 2.6 times the total thickness (inches) of the carpet.
Most conventional carpets are suitable for use over heated floors, but it is recommended that you consult with the manufacturer first to see if the backing is suitable for long periods of low heat.
Click Here to Learn Floor Covering Considerations from The Carpet and Rug Institute.
Hydronic Heating in the Walls and Ceilings
Hydronic radiant heating can be used in the walls and ceilings, although the availability will be dependent on the particular manufacturers. Heating the walls and ceiling is viewed as a good idea if there is any doubt that floor heating alone can be used as the primary heat source. Radiant wall and/or ceiling systems are an excellent solution when a room will have carpet and pad or some other thermally resistive finished floor. Some rooms, such as kitchens and bathrooms, have much of the floor occupied by base cabinets, islands, fixtures, appliances, and other objects that reduce the useable portion of the floor compared to the room as a whole. These rooms usually have largely unobstructed ceilings which provide ample heat to the room.