Before any underfloor heating goes down, whether it's an electric mat, a loose cable or hot-water tubing, the subfloor has to be flat, solid, clean and dry. On a concrete slab it also needs insulation under the heat, so the warmth rises into the room instead of soaking into the ground. After that, the floor you want on top sets the rules: how deep the heat is buried, how warm the surface may get, and how long the system runs before we install.
Porcelain and ceramic tile are the easiest floors to heat. The cable sits in thinset or on a heating membrane right under the tile, but tile needs the flattest, stiffest subfloor of any floor.
Luxury vinyl plank (LVP) goes over heat that is built into the subfloor, under a layer of concrete or leveler, with the surface capped at 82 to 85 F. A loose electric mat under a floating plank is only an option when that plank's maker approves it.
Laminate needs the heat embedded in the subfloor as well, with the surface held to 82 to 84 F and the heat running for two to three weeks before installation.
Engineered hardwood is the wood floor to put over heat. Expect the heat to run for a week before we install, a surface cap of 80 to 85 F depending on whose guideline you follow, and a humidifier in winter.
Carpet works over a heated floor when the carpet is low and the cushion thin and dense, because a thick carpet on a thick pad holds the heat down in the floor.
Tile asks the most of the subfloor itself, while vinyl, laminate and wood ask the most of the heat under them.
| Floor | Heat it can go over | Surface limit | Subfloor must be |
|---|---|---|---|
| Porcelain or ceramic tile | Electric mat or cable; hot water | About 85 F, for comfort | Flat to 1/4 in over 10 ft; stiff |
| Natural stone tile | Electric mat or cable; hot water | About 85 F, for comfort | Twice as stiff as for ceramic |
| Luxury vinyl plank | Heat built into the subfloor | 82 to 85 F by maker | At least 3/8 in over the heat |
| Laminate | Heat embedded in the subfloor | 82 to 84 F by maker | At least 1/2 in over the heat |
| Engineered hardwood | Hot water or buried electric | 80 to 85 F | Heated a week before install |
| Carpet | Hot water or electric | Backing must take steady heat | Carpet and pad R-4 or less |
How to prepare a subfloor for underfloor heating
Preparing a subfloor for underfloor heating follows the same order whether the heat is an electric mat under bathroom tile or hot-water tubing under a whole first floor. Only the numbers change, and those come from the floor going on top.
- Repair, clean and flatten the subfloor.
- Test a concrete slab for moisture, and give new concrete its full drying time.
- Put insulation between the slab, or the joist space, and the heat.
- Lay the heat out to its maker's plan, clear of cabinets, tubs and other fixed fixtures, with the floor sensor between two runs.
- Test electric cable with an ohmmeter and record the readings.
- Bury the heat to the depth the finished floor calls for, then let that layer cure with the heat off.
- Install the floor under its maker's temperature rules, and bring the heat back up slowly.
How flat and clean the subfloor has to be
A flat subfloor shows no dips or humps under a long straightedge, which is a different thing from level. Tile has the tightest limits: for tiles with every side under 15 inches, the floor can vary no more than 1/4 inch over 10 feet, and once any side reaches 15 inches, that tightens to 1/8 inch. Vinyl plank, laminate and engineered wood makers typically ask for 3/16 inch over 10 feet.
We flatten concrete and wood the same way. High spots get ground down, low ones get filled with patch, and where a whole area is out, self-leveling underlayment goes on over a primer. That's a cement-based pour that spreads to its own level and cures smooth and hard. Over a heated floor, the same leveler often becomes the layer that buries the cable, so getting it flat pays off twice.
Clean matters because thinset and leveler have to bond to the subfloor. Old adhesive gets scraped off, and dust, grease and paint overspray come off before anything is spread.
Fix squeaks, soft spots and loose panels first
A wood subfloor that squeaks, gives underfoot or has swollen seams gets fixed before any heat is buried in it. Once the heat is under leveler or tile, the only way back to the subfloor is to break the floor. Loose panels get screwed to the joists, soft or water-stained panels get replaced, and swollen edges get sanded flat. For the warning signs, from squeaks to a marble that rolls on its own, see our guide to why your subfloor matters more than the floor you choose.
Insulation under the heat
Insulation under the heat decides which way the warmth goes. Concrete soaks up heat, so on a slab, insulation board goes between the concrete and the heating cable, and more of the heat reaches the floor instead of warming the slab. When tubing or cable hangs under a wood subfloor in the joist bays, reflective insulation goes under it to send the heat up.
Skipping it can also cost you the floor. When the National Wood Flooring Association looked into wood floors that failed over radiant heat, it found systems run too hot for too long and no humidity control. In some homes, missing subfloor insulation had kept the heat running longer than normal.
How deep the heat is buried
Every heated floor has its heat buried in something, and the finished floor decides how deep. Under tile, the cable sits in the thinset or in a heating membrane just beneath the tile. Under vinyl plank, laminate and carpet, electric cable gets about 3/8 inch of self-leveling underlayment over it. Many floating floors also set a minimum distance from the heat, commonly 3/8 to 1/2 inch.
Hot-water tubing is buried the same way on a bigger scale. It goes in the slab itself, in a poured layer of lightweight concrete or gypsum over a wood subfloor, or in grooved panels with aluminum plates that spread the heat.
Whatever covers the heat has to cure with the system off. Thinset and leveler over electric cable take from 2 to 28 days to cure, and turning the heat on early can leave the layer brittle and damage the cable inside it.
Testing the cable before it is covered
Electric heating cable is tested with an ohmmeter, not by switching it on. The resistance is read out of the box, again once the cable is laid, and again after it is covered. Each reading goes on the warranty card that comes with the system. A reading that changes means the cable may be damaged, and that's far cheaper to find before the tile or planks go down.
Photograph the whole layout before it disappears, with a wall or doorway in each shot. Years from now, you'll know where the cable runs, where the floor sensor sits and where a baseboard nail can safely go.
Heated floors on a concrete slab or in a basement
A heated floor on a concrete slab has two problems to solve before the heat goes in: warmth draining into the concrete, which the insulation handles, and moisture coming up out of it. Plenty of homes around Huber Heights and Dayton sit on slabs and basements, and our summers are humid. A slab that tests dry in January can read damp in August, so a passing test is a snapshot, and we treat it that way.
Testing a slab for moisture
Two tests show up in the floor makers' instructions. The in-slab relative humidity test (ASTM F2170) sets probes into small holes drilled in the concrete and reads the humidity inside it. The calcium chloride test (ASTM F1869) measures how much water vapor the surface gives off over a few days. A handheld moisture meter is only a quick screen.
Wood is the fussiest about a damp slab and vinyl plank the most forgiving, going by the limits in the makers' own instructions.
| Floor over the slab | In-slab humidity (F2170) | Vapor emission (F1869) |
|---|---|---|
| Bruce engineered hardwood | 75% or less | 3 lb or less |
| Inhaus laminate | 75% or less | 5 lb or less |
| Mohawk laminate | Under 80% | Under 5 lb |
| Mohawk vinyl plank | Under 90% | Under 8 lb |
Vapor emission is counted in pounds per 1,000 square feet over 24 hours. A slab that tests too wet gets the same fixes it would need under any floor, and our guide to moisture management in subfloor preparation walks through them.
New concrete and new pours over tubing
New concrete holds a lot of water, and a heated slab has to give it up before any floor goes down. Mohawk's rule is at least a week of drying for every 3/8 inch of thickness up to 1-1/2 inches, and twice as long beyond that. A 2-1/2 inch pour needs about eight weeks.
With hot-water heat, running the system is part of the drying. Floor makers want it running before installation for anywhere from a week for engineered wood to three weeks for some laminate. That run also proves the system works before a floor covers it.
Vapor barriers depend on the floor
A plastic vapor barrier belongs under some heated floors and not others. Floating laminate over a slab goes on a 6-mil polyethylene sheet or an underlayment with the film built in. Tile needs the opposite, because thinset has to bond to the surface under it, and a plastic sheet would leave it nothing to grip.
For a heated basement, we recommend the same floors we'd recommend for any basement. That means porcelain tile, engineered wood when the slab tests dry enough, and the waterproof luxury vinyl plank we install in basements across the Dayton area.
Radiant floor heating on a wood subfloor
Radiant floor heating can go on a wood subfloor in three positions. On top, it's buried in leveler, thinset or a thin poured layer. Within, it runs through grooved panels or between wood strips called sleepers. Underneath, it hangs in the joist bays from the basement or crawlspace, with reflective insulation under it. The floor going on top, and whether you can reach the joists, decide which one fits.
How stiff a wood floor must be for heated tile
A wood-framed floor under tile has to be stiff, with or without heat. The Tile Council of North America's baseline is a floor that bends no more than its span divided by 360, written L/360. On joists spanning 10 feet, that's about a third of an inch at the middle under load. Natural stone needs a floor twice as stiff, L/720, which over wood framing with backer board means two layers of plywood.
Joists set 24 inches apart can meet the span rule and still flex too much between the joists. That's why the tile industry's installation methods, not the deflection number alone, decide how thick the subfloor has to be. If your floor bounces underfoot or the joists sit 24 inches apart, plan on stiffening it before tile; it's one of the things we check with you at the free measure.
Poured layers over a wood floor
A hot-water system poured into lightweight concrete or gypsum over a wood subfloor adds real weight. Have an engineer confirm the framing can carry it before the pour, and let the pour dry fully before a floor goes on it.
Nails, staples and tack strip over heat
Anything driven into a heated floor has to miss the heat. Staples, flooring nails and the nails that hold carpet tack strip all stay clear of the tubing and cable, so mark the runs on the subfloor or in your photos before anything covers them. Where electric cable runs under nailed hardwood, the cable sits between sleepers under a leveler, and the boards are nailed only into the sleepers.
Choosing between electric and hydronic heated floors
Electric floor heat suits a single room, and hot-water, or hydronic, heat suits a whole floor or house. Electric mats and cables are thin and fit a bathroom, kitchen or basement room. Hydronic heat pumps water warmed by a boiler through tubing, and it's the most popular and cost-effective radiant system in cold-winter climates like ours.
Running cost is the catch if you want electric floors as your main heat. Because electricity costs more, electric radiant floors usually pay off as whole-house heat only when a thick slab stores the warmth and your utility offers cheaper off-peak rates.
Hydronic heat is designed for the house. A heating contractor starts with a heat-loss calculation for each room, which shows whether the floor can warm that room at a temperature your floor covering allows. Either way, the system should run on a thermostat with a sensor in the floor, set to the surface limit of the floor on top.
Can you put heated floors under LVP?
Yes, heated floors can go under luxury vinyl plank, as long as the heat is built into the subfloor and the surface stays under the maker's cap. Vinyl plank is thin and passes heat well. On an existing slab, that usually means electric cable covered by a cement-based leveler, where the plank's maker allows it.
Mohawk accepts hot-water or electric heat that's built into a cement subfloor. Its vinyl plank wants the surface at 82 F or less, and the room and floor held between 65 and 85 F while the planks acclimate, go down and settle for 48 hours. A transition strip goes where a heated room meets an unheated one.
MSI allows only hot-water heat under its rigid-core planks, at least 3/8 inch beneath them. The system runs for two weeks first, gets turned down to 65 F five days before we install, and comes back up afterward to no more than 85 F.
Neither maker signs off on a floating vinyl floor laid straight onto an electric mat. Not every plank is approved for heat, either. Our online luxury vinyl collection has a Radiant Heat Approved filter, so you can see which floors qualify before you fall for one.
Heated wood floors
Yes, wood can go over radiant heat, and engineered hardwood is the wood to choose. Its cross-layered core moves far less than a solid board as the heat dries it, which is why engineered is the usual recommendation over radiant heat.
Wood also has the lowest temperature cap, and the guidelines disagree on it. The National Wood Flooring Association holds a wood floor's surface to 80 F, while Bruce allows up to 85 F for its engineered floors. Follow the maker of the floor you buy. If a room's heat-loss numbers need the floor warmer than that, the room needs a second heat source rather than a hotter floor.
Bruce's instructions add a routine around installation day. The system runs and heats for at least seven days first. It then goes off long enough for the subfloor to cool to room temperature, three or four hours, and comes back on as soon as the floor is down. The boards get glued at their ends to limit shrinkage, and the heating circuit should serve only rooms with wood, so the floor is never heated to suit the tile next door.
Radiant heat also dries the air, and the same instructions ask for 30 to 50 percent relative humidity. In a Miami Valley January, that usually means running a humidifier. A thermostat that limits the floor temperature, which the wood flooring association recommends, keeps the surface from creeping past the cap on the coldest nights. We install engineered and solid hardwood across the Dayton area and will tell you at the measure which one suits your subfloor and your heat.
Laminate over radiant heat
Laminate goes over radiant heat when the heat is embedded in the subfloor and the plank is approved for heat. Inhaus wants at least 1/2 inch between the heat and its planks, and the heat running for three weeks before installation. The surface can never pass 84 F, and the heat should cover the whole room or stop at a transition molding.
Mohawk's laminate is stricter on temperature, and it goes down on a floor no warmer than 64 F. After 24 hours, the heat comes up no more than 5 F a day and never past 82 F, and every later change follows the same 5-degree step. The same instructions call a little seasonal gapping normal over radiant heat and ask for 45 to 65 percent humidity. They also limit foam underlayment to 1/8 inch, with a 6-mil plastic film under it or built into the pad.
Every layer over the heat slows the warmth, so use the thinnest pad your laminate's maker allows. The foam, felt and cork options in our guide to choosing laminate underlayment all insulate to some degree.
Not every laminate is approved for heat. Our laminate collection has the same Radiant Heat Approved filter as our vinyl.
Tile and stone on a heated subfloor
Porcelain tile is the floor that heat works best under. It passes heat quickly and barely moves with temperature, which is why MSI, whose porcelain and ceramic tile we carry, calls it the top performer over radiant heat. Natural stone holds its warmth after the system cycles off.
Under tile, electric cable goes in one of two ways. It can be embedded in a skim coat of modified thinset, with the tile set on a second layer. Or it clips into a heating membrane bonded to the subfloor with the mortar that membrane's maker specifies. The membrane suits wood subfloors, because it also absorbs small movements between the subfloor and the tile.
Over wood framing, the floor still has to meet tile's stiffness rule: L/360 for ceramic and porcelain, and twice as stiff for stone.
Tile needs room to move at its edges, on a heated floor as on any other. That means an open joint about 1/4 inch wide at every wall, cabinet and pipe, kept clear of mortar and grout.
Can you put carpet over radiant heat?
Yes, carpet can go over radiant heat, and its thickness decides how well the heat gets through. The Carpet and Rug Institute says most radiant heating makers want the carpet and cushion together at an R-value of 4.0 or less. R-value is an insulation rating, and a rough guide for carpet is 2.6 times its thickness in inches. A low pile over a thin, dense cushion keeps you well under the limit.
Some electric cable systems set a lower cap, about R-1 for the whole floor covering, which is roughly what 3/8-inch carpet reaches on its own. Under electric heat, the heating system's limit decides the pad. Heat hung under the subfloor already has to run warmer to get through the wood, and carpet slows it again, so that pairing needs a heating design that allows for both.
On installation day, tack-strip nails have to miss the tubing or cable, and glue-down carpet goes in with the heat turned down so the adhesive doesn't dry too fast. Most carpet does fine over a heated floor, as long as its backing can take long periods of low, steady heat.
Who does each part of a heated floor installation
A heated floor installation is usually three trades' work, and the order matters more than who you call first. The flooring side is ours: the subfloor repairs and flattening, the moisture check and the finished floor on top.
The heating system goes in to its own maker's instructions. Electric mats and cables get their final connection from a licensed electrician, on a ground-fault-protected (GFCI) circuit, with a thermostat that reads the floor. A hot-water system is designed and installed by a heating contractor.
Settle the floor first, then plan the heat around it. The floor decides how deep the heat is covered, how warm it can run and how long it runs first. A floor's installation instructions are also the conditions its warranty follows, so confirm the floor is approved for your heat before anything is ordered.
We sort that out at the free in-home measure, looking at your subfloor, the heat you have or plan, and the floor you want. We handle installation for every kind of floor we sell, from tile and vinyl plank to laminate, hardwood and carpet.
Heated floor questions we hear
Can you put a rug on a heated floor?
Yes, a thin rug is fine on most heated floors, though Mohawk asks for no area rugs on its laminate during the heating season. A thick rug or mat traps heat, so the floor under it runs hotter than the rest of the room. Rubber- and vinyl-backed mats can break down in the heat and stain the floor. Keep rugs and box-bottomed furniture off the spot where the floor sensor is buried, or the thermostat will misread the room.
How much height does a heated floor add?
It depends on the heat under the floor: electric cable adds about 3/8 inch of height under vinyl, laminate or carpet for the leveler, plus any insulation board beneath it. Under tile, the cable sits within the thinset or membrane layer. A hydronic pour over a wood subfloor adds the full thickness of the pour. Plan door clearances, transitions and the dishwasher opening before the heat goes in.
Can you add heated floors without tearing up the floor?
Yes, if the room sits over an unfinished basement or crawlspace. Hot-water tubing or heating cable can go up into the joist bays from underneath, with reflective insulation under it, and the finished floor stays put. Because the heat has to pass through the subfloor and the floor, this method runs the system hotter than a buried one. The floor on top still has to be approved for radiant heat.
Can you turn a heated floor down at night?
No, not by much. A thick slab takes hours to respond, so hot-water slab systems are meant to hold a steady temperature. The floor makers also limit how fast the surface temperature can change, some to a few degrees a day for the life of the floor.
Planning a heated floor with us
The best time to call us is before the heat goes in, while the cover depth, the temperature cap and the floor itself are still choices. Request a free estimate, and we'll come out, look at your subfloor and help you choose a floor that's approved for the heat you want.
