What About New Floors Over Radiant Heating
If the previously written-upon question has been settled and your Radiant
Heating System is in place, or definitely will be, then we’ve got some tips
for you to factor into choosing and installing your new
floor covering. These are general, of course, so make sure you verify, dismiss or tweak
them based on what your actual manufacturer’s instructions say.
If the radiant system has just been installed
If it has been embedded in concrete, then before putting any flooring over a
newly installed radiant heating system, it is usually recommended to run the
system for up to six days. Some say three to six, some five to six, so
absent anything specific in your documentation we recommend the full six
days. This is done to eliminate any residual moisture from the concrete
poured over the system. It’s a lot of extra time, we know, but it is worth
it to avoid having this moisture instead rise up into your flooring,
especially if it’s wood based and very responsive to environmental
If the whole concrete slab is new, above and below the system such as in a new home or an addition, you might need to extend this drying time quite a bit. For concrete under two months of age this drying step may need to go a full month or even two months to ensure that all the excess moisture can be released from your subfloor.
Regardless of the subfloor type, you will always need to know where the tubes or coils are located, so once it’s installed, mark your subfloor to indicate where they are and which directions they run. If you ever need to install something by nailing or boring into the subfloor, this will help you avoid piercing one of those tubes. Repairing these just has to be a big pain.
Issues for All Floor Coverings
The primary issue with floor coverings and radiant heat is the heat, and what it can do to certain materials. In a central heating situation the floor is almost always very close to the same temperature as the room, heated or cooled by the same air that is cooling you – a slow change. With radiant heating, it’s more like a heating pad. Think about how different the temperature is when you touch a heating pad (such as one you might use for your back) vs. hovering your hand 1/4″ to 1″ above it. Big difference. Now compare that to being anywhere from 5″ to 30 feet away, where the differences become almost imperceptible.
Flooring over radiant heating is more like that 1/4″ to 1″ zone, very close, so it can be much warmer than the rest of your room might feel, and the changes in temperature can happen much more swiftly.
Most flooring has a range of temperatures within which it is warrantied. These always include ranges considered normal for human comfort, but some products will have very specific numbers to consider for both the temperature of the room, and the temperature setting for any radiant heating system.
Also, almost all floors need to be acclimated to their new rooms before they are installed. Factor your radiant heating system into that process. Usually it is recommended to have it on for the duration of this step.
Best Floor Covering Options over Radiant Heat (in order!)
Any Stone Tile, including Ceramic and Porcelain
These are all but made for under-the-floor heating. Stone like materials both conduct and hold heat very well. They’re natural, but don’t expand or contract with environmental changes like every other natural floor product will do. This means that cracking from the heating system is not a worry, only from the dropped anvil.
We’re not usually too friendly with carpeting on our ‘Best Floors For’ lists (for allergies, for kitchens, etc.), but here’s a place where it really rates. Carpet’s particular set of cons don’t really come into play with radiant systems. Like the stone products, is not prone to changing shape with changes in temperature. It’s already designed to be warm underfoot, but it comes in below the stone products because it does not radiate the heat from below as well. It will take longer to heat the entire room than it would with stone, because carpet acts as a bit of an insulator. The shorter the top layer of your carpeting, the better it is for this kind of heating system.
If it’s going over concrete, make sure to look at the tips above, and check your documentation. Laminate does react to environmental changes, both temperature and moisture, so dryness of the subfloor is essential. You should expect the documentation to contain setting limits for your heating system, such as “Radiant heat never set above 81 degrees.” You’ll be better off with a floating floor, which is by far the most common kind of laminate anyway, but if you do choose a glue down product, also check the documentation on the adhesive you will be using.
Regardless of whether your subfloor is concrete, before installation of any kind of hardwood you will wind up running your heating system for at least a week. It should be on for 3 days before you even put the wood into the room to acclimate, then it will be on while the wood acclimates to the standard temperature and moisture content of the room. Most hardwoods recommend five to seven days just for that step. Get these things used to each other and you can save yourself future issues.
With hardwood it is especially important to install the planks perpendicular to the direction of the heating tubes. This will help even out the distribution of the heat. If the planks are parallel, one might completely rest above a heating tube, while the next one is over no heating tubes, making each plank a different temperature.
It is also especially important to make sure your particular choice can go over radiant heating, because here we’re not just dealing with manufacture and design of a product, but with the differences between various species of wood. You could get the same series of flooring from the same manufacturer, with all the same specs as far as plank sizes, and yet one species may be fine while another might not even be an option because of the nature of the species of the woods. Always be very specific with real wood. Check installation instructions, and check the warranty. Those are your best sources on limitations for any floor.
Once installed, as seasons or temperatures change, don’t suddenly jolt your temperatures up and down, but change them gradually. It’s probably better for the system, but it will definitely be good for the wood to get used to the changes.
It is the only one of the two types of hardwood flooring that can be put into a basement, and this also makes it the better choice for going over heating under the floor. Unlike solid, engineered hardwood floors can be floated, which makes them able to go over concrete and avoids need for adhesives (or nails!).
Solid hardwood is not even able to go into a basement where many Radiant systems are used. Aside from that it can be used, but these tips should give you the best chances of success:
Because both heat and moisture are at issue, you will have better luck with real wood if you live in a dry climate, and with the driest possible concrete, if that’s your subfloor. It’s just one less issue to factor in.
Try to get hardwood that is kiln-dried. Kiln drying is a process that pushes a lot of moisture out of lumber. This adds dimensional stability.
Look for boards made from lumber that was quarter-sawn, one of the three main ways lumber is cut into planks. Without getting into milling and carpentry, we’ll just say that this method produces boards with greater size stability and resistance to warping.
You might think that a roomful of wood is a roomful of wood, but the cut does matter. Narrower boards actually shrink and expand less than wider ones, as a percentage of the overall size. What we call hardwood strips (basically anything less than 3″ wide) also have more gaps to accommodate any changes that do happen, so whatever change is inevitable can be less noticeable.
Vinyl is last. Some vinyl floors will work over radiant heating, but all of those will have some temperature restrictions, so pay close attention to those with these floors. Also, vinyl is a much better insulator than it is a conductor, so it will actually be working against your heater. Some vinyls simply cannot go over this heating system, and may release some bad chemicals if ‘baked’, to say nothing of changing color.
If your manufacturer says you can use it, then you can, safely, used according to their guidelines. If the manufacturer of your specific floor choice says no, then you should follow this advice over anything we’ve laid out here.
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David is has written and made videos about flooring products and installation since 2011 at Floors To Your Home (.com), where he is also the PPC Manager, a Researcher, a Website & Marketing Strategy Team member, Videographer, Social Strategist, Photographer and all around Resource Jito. In my spare time I shoot and edit video, put together a podcast, explore film history, and mix music (as in ‘play with Beatles multi-tracks’). Connect with W. David Lichty
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