Floor Heating Electrical Requirements: When to Use 120V vs. 240V

When it comes to voltage, most of us don’t have to give it much thought until we travel overseas or shop for major appliances. But having a basic understanding of voltage is important when choosing floor-heating mats or cables so you can find the right product to help ensure years of trouble-free enjoyment. But how do you choose between 120V and 240V? You might turn to an online forum and get well-meaning but bad advice that could lead to added costs. Instead, read this guide to help you select the right voltage for your floor-heating project.

Is voltage the same as power?

No. A product’s voltage rating doesn’t indicate how much power it uses. Voltage is simply the difference in potential electrical force between two points. But what does that mean? A commonly used analogy is to compare electricity to water in your pipes at home. Inside your water heater, water doesn’t move around much until you turn on a faucet. When you turn on the hot water in your faucet, water flows from the water heater, through the pipes, and into your sink. The water pressure is the voltage (V), controlling the speed and force at which the water flows out. The amount of water flowing would be the amperage (I). And power (P) in watts is the voltage multiplied by the amperage, which tells you how much power is being used. This useful formula lets you calculate Watts : P = V x I .

Electrical requirements for radiant floor heating systems

240V vs 120V floor heating products

Is it true that 240V products generate more heat, heat up faster, cost less to run, and work more efficiently than 120V?

No, no, no and no. This is a big misconception that pops up in Internet forums. Let’s say you take two mat systems of the same square footage, one 120V and the other 240V. If they are designed with the same watts per square foot (the industry standard is 12 W/sf), both products will use the same amount of watts and use the same amount of power. This is because a 120V system draws twice the amps per square foot of a 240V system, and that a 240V system draws half the amps per square foot of a 120V system. Ohm’s law tells us that when voltage decreases, amps increase proportionally. For example, let’s say you want to heat a 100 square foot area. According to the manufacturer’s specs, we know both systems use about 1200 watts, and we know the voltage, so we find the amps by using the formula : V x I = P, or P / V = I. (This formula is part of Ohms law, which requires a Resistance value also):

240V 120V
1200 watts / 240 volts = 5.0 amps 1200 watts / 120 volts = 10 amps

So while the 240V sounds like it has twice the power, it generates the same amount of heat (watts) per square foot as the 120V system, heats up at the same rate, and would cost about the same amount per square foot to heat the floor. And for standard power supplies of 120V and 240V, matching products are equally efficient (120V to 120V vs. 240V vs. 240V).

Browse Products by Voltage:

Do cables or mats need to match the voltage of the power source?

Yes. We’ll get into the why below, but if there’s one important takeaway about voltage and floor heat, it’s that the voltage of your mat or cable product should match as closely as possible the voltage of your power source. Almost all homes in the USA and Canada have 120 and 240 VAC available in their electrical panel. If you want to use an existing circuit, choose from what is available. If you are running a new circuit and the heated floor is smaller than 120–150 square feet, we always recommend 120V . You can choose 240V, for a new circuit for small areas, but it will cost you more and take up an extra slot in your panel. In general, the square footage of the area you want to heat is one of the main factors in choosing between 120 and 240V products, which we’ll get to next.

So why choose a 240V over a 120V system, and vice versa?

At Warm Your Floor, we recommend 120V systems for heated areas less than 150 square feet (at 12 W/sf), and 240V systems for heated areas more than 150 square feet. The reason for this is a single thermostat can control 15 amps. Using the numbers in the previous question, 120V systems draw more than 15 amps over 150 square feet, so manufacturers offer 240V systems for larger areas. Using the example above, a 240V system could heat up to 300 square feet and still be controlled by a single thermostat.

Sometimes, a customer’s power supply is rated with a nonstandard voltage. A few of the outdoor products Warm Your Floor carries can be special ordered from the manufacturer (SunTouch and Nexans are two) to match specific requirements. Which brings us to the next question…

What happens when a product’s voltage rating doesn’t match the voltage of the power supply?

We’ve covered the fact that you’ll want to match your power source voltage to your mat, but what would happen if a 240V mat is connected to a 120V power source?

A 12 watt per square foot SunTouch mat would output only 25% of its heat. This would be not at all effective in heating your floor.

In the reverse case, connecting a 120V product to a 240V power source will overload the system y increasing the heat output to 4 times the normal, causing damage to the mat and thermostat, premature failure, and costly reinstallation.

But in special cases, you’ll need to mismatch voltages between the power source and the floor-heating products. The standard voltages Warm Your Floor carries are 240V and 120V, but some customers have indoor power supplies rated at 208V. In this case, a higher voltage product rated at 240V can be connected to a lower voltage power supply at 208V, but the heat (watts per square foot) generated will be reduced by 25 percent, running at 75% power. To find this number, we divide the lower voltage by the higher voltage and square the result:

(208V / 240V)² = .75 = 75%

To make up for this 25% reduction, some manufacturers recommend spacing cables slightly closer together, so more cable would be needed to heat a smaller area. But this method is limited by the 15 amp max load for the thermostat. And it doesn’t work with all products, as some manufacturers require a set distance between cables. We can recommend floor-heating products that provide more watts per square foot to offset this reduction. But be sure to consult a qualified electrician to help you plan a layout that meets your needs safely and effectively.

Getting your project started with Warm Your Floor

Have more questions? Contact us today and we’ll help you find the right products for your floor-heating project.

65 thoughts on “Floor Heating Electrical Requirements: When to Use 120V vs. 240V”

  • Bruce Lawson says:

    I’m enclosing a deck to a 3 season porch. I want to use a 240volt system but not sure on wire type. I pretty sure it need to be 12AWG with a 20amp breaker but not sure if I need 12/2 with just a black,white, and ground or 12/3 with a black,white,red and ground.. I’ll be roughing in wire soon and would like to be certain before I spend the money.

    • Hi Bruce,
      You just need 2 conductors + ground, for either 120v or 240v systems
      If the area is over 150 SF, 240v is the way to go.
      Wire size is dependent on amp load, as I’m sure you know.

      At 240v, 0.05 amps per SF, up to a maximum of 15 amps on a 240v dedicated circuit, so 300 SF @ 12 watts/SF

      If you’d like us to put a quote together for you – visit our quote page and we’ll respond in 24 hours or less, or give us a call

      https://www.warmyourfloor.com/quote-request

      Warm Regards,
      http://www.WarmYourFloor.com
      The Radiant Floor Heating Experts™
      Orders & Support 866-558-3369

  • Joe Motyka says:

    I want to heat a floor area behind my basement bar. It is only a 3 foot by 8 foot area. (24 sq ft)

    This existing 15 amp circuit with 14 gauge wire. It has 2 outlets ( Not used all the time and a compact refrigerator. )

    I calculate the amp draw on the floor heat to be only 2.75.

    Do you think that I could safely hook up the floor heat to this circuit ?

    Please let me know,

    Thank you,
    Joe

    • matthew@warmyourfloor.com says:

      Hi Joe,

      The floor heat would draw a little lower than that, 2.4 amps.

      Assuming this is connected to a 20 amp breaker, you should be able to add the floor heat to the existing circuit.

      Always check with an electrician though if you’re not certain.

  • The space I am heating is 300 sqft. I know I need a 240v system but the largest system you sell is 240 sqft. Can I add an additional 60 sqft to this system? Will the thermostat handle? If possible, how is the connection made?

  • Hi, I’m in Ontario and currently roughing in electrical for use at a later date. If I run 12/2 from my panel area to the future thermostat locations, will that be sufficient when I have an electrician come and do the radiant floor install? It is for 3 small areas. 1) is aprox 70 square feet, 2) is approximately 25 square feet and 3) is 16 square feet. I was planing on having the larger area on its own 15A GFI circuit and the smaller two run off of another 15A GFI circuit.

    • matthew@warmyourfloor.com says:

      Hi Pete,

      That 12/2 wire will be enough for the electrical load.

      You can control anywhere from 133 – 150 sq ft on a single 20 amp breaker at 120V.

  • Moved to older home with several Infloor heating zones. How to identify which floor has heating if the controller has been removed on past renovations? The breaker box has three Infloor heating breakers marked. 1) a single 20Amps breaker that powers the kitchen floor (tile) and thermostat. 2) a double 20Amps breaker that powers the lower bedroom cement floor and thermostat. There is a 3rd double 20Amps breaker which I have not identified what it controls. The other floors are hardwood. Are there non destructive ways to identify an underlying in floor heating and then trace for the area the thermostat would be positioned?

  • Hello, I am planning to tile a floor that is 15ftx25ft. if I get 2 mats that are 24inches x 60 ft will I then need two thermostats?

    • matthew@warmyourfloor.com says:

      Hi Rocco,

      You would be able to control both those mats on one thermostat so long as they are 240V products.

      Always make sure you check the amp draw of each mat and don’t overload the thermostat with more than 15 amps.

  • hello,
    I’m planning on making a shed into a house but i wanted to see what would best for me. the shed is 16ft x 32ft and two levels

  • Hello. I am redoing my basement. I have about 700 sq ft in the living room that we want to heat. I was figuring on hearing about 400-450 sq ft of it. So I know I need 220v, but covering that much space, will I need 2 thermostats?
    Also, will I put the mesh on the concrete and then mortar and the ceramic tiles or do I need to put something else over the mesh before I set my tiles?

    • matthew@warmyourfloor.com says:

      Hi Cody,

      You would need a second thermostat or a relay for an area that size.

      And yes, that’s the correct method the mesh mats get installed.

      Mesh mat goes onto the concrete, thinset on top, then tile.

      Let us know if you have any other questions.

      Thank you, Cody.

  • I’ve got a 240 volt forced air heater and thermostat on a dedicated circuit in my bathroom right now. I’m hoping to switch to a 240V radiant mat system. Can I use the thermostat and heater wiring that is already in place to connect a new thermostat and floor mat? Thank you.

  • Daniel Fernandes says:

    Hello
    I’m looking to replace an existing mud room tile floor – currently heated with a single 240 v 20 A baseboard. Floor is 19′ x 8′. What options do I have for under new tile floor heat mat? Can I do a direct power connection to the new mat? Can I get a single mat to accommodate the floor size? Any detail will help my decision making.

    Thanks,
    Dan

  • Rick Wadsworth says:

    I had 2, 240V base board heaters and then decided to change one of them to infloor heating. I told my installer that it was 240 V. They missed that information. they did the infloor heating and thermostat with 110 V wiring . The other base board heater on the line is very rarely used , in fact I do remember ever using it. The installer changed the panel wiring to make the 240 V Wiring put out 110 V. The infloor area is only 20 sq. ft. shoud I worry to much about changing out the base board heater to 110V?

    • matthew@warmyourfloor.com says:

      Hi Rick,

      Thank you for contacting us today!

      Most thermostats these days are dual voltage, but check to make sure.

      But the voltage of the incoming power MUST match the voltage of the product in the floor.

      So if the heating cable is 120V, then the incoming power must also be 120V.

      So long as the heating cable and the power are the same voltage, the system will work fine.

  • I’m looking at purchasing a system from you for just under 100 sq ft space of in floor heat. I’d like to remove the existing baseboard 2000watts 240 volt and install in floor heating instead. There are a couple other baseboards on that 20 amp 240 circuit (with their own separate thermostats). Can the in floor heat share a 20 amp circuit with 2 other baseboards on it or does it have to be a dedicated circuit? They are 1000 watt baseboards so I think from a total load perspective I should be fine.

    • matthew@warmyourfloor.com says:

      Hi Dave,

      Thank you for contacting us today!

      What it comes down to is if the 20 amp circuit can handle the load.

      All floor heating manufacturers will tell you to put the floor heat on a dedicated circuit and it not be shared with any other devices.

      A 100 SF cable at 120V will draw 10 amps, but at 240V would only draw 5 amps.

      If the circuit can handle the 5-10 amp load from the floor heat, along with the load from the baseboard heaters, then it will work.

    • matthew@warmyourfloor.com says:

      Hi Lind,

      Are you trying to determine which size wire you need to run for the power to the system?

      A 12 AWG wire would suffice, if the load will be 12 amps or less, you can get away with using a 14 AWG wires in that case.

  • I have an existing wire (10/4 AWG – 240V) which was used for a jacuzzi 20A double braker GFCI protected . Can I use the 240V system for this wiring (120 sq.ft)

    • matthew@warmyourfloor.com says:

      Hi Kris,

      Yes, you could use the existing wire and circuit for the floor heating system.

      You need to make sure you purchase 240V product though so it matches the voltage of power coming in.

      You may want to change the breaker to a non-GFI protected breaker though.

      The thermostat has GFCI built in, and if it is connected to a breaker that also has GFCI protection, then the circuit tends to have nuisance trips.

      Let us know if you have any other questions.

      Thank you, Kris!

  • Charlie Cruickshank says:

    I have a 400 sq. Ft. Room that I’ve installed (2) 240v wired systems. Due to amperage draw I have a relay between the two systems and the thermostat. I have 240v coming from the breaker panel to the thermostat, and then 240v to the input of the relay; however I’m getting nothing from the relay output to the floor wires. Any ideas of what I may have done wrong? The floor wire all tests out fine. Thank you for your help-

    • matthew@warmyourfloor.com says:

      Charlie,

      This sounds like either something is not connected to the relay properly or the relay may be defective.

      Check all the connections and make sure the wires are in the correct terminals on the relay.

      If everything is connected correctly, check with the manufacturer if the relay is defective.

    • matthew@warmyourfloor.com says:

      Hi Randal,

      Our thermostat are designed to operate a floor heating system and would not work to control your baseboard heater or vice versa.

      If you have a floor heating system, you’ll need to purchase a floor heating thermostat.

      The baseboard heater you have will require a different type of thermostat which we do not sell.

    • matthew@warmyourfloor.com says:

      Hi Paul,

      For either voltage, the max is 15 amps.

      The SF depends on the product, but for Nuheat or SunTouch mats it’s 150 SF @ 120v and 300 SF at 240, Schluter can cover slightly less.

      We’d be glad to take a look at a sketch or floor plan of your area(s) and provide options to help you determine the best solution and provide a quote!

  • After 3 years our in floor heating stopped working and the GFI light keeps flashing. I found out the fellow put in 120 volt heat cable into a 240 panel. Would that be the cause?

    • matthew@warmyourfloor.com says:

      Hi Debbie,

      Yes, that’s the problem.

      Make sure to turn off the breaker because you are overheating your system with too much voltage; the voltage of cable and circuit breaker must match.

      The miss-match in voltage has most likely caused the thermostat to fail.

      The heating element in your floor is probably okay, but it should be tested too.

      Changing the circuit breaker from 240v to 120v may be easy but I’d get an electrician in there.

      And best to buy a replacement thermostat before, maybe the electrician can take care of everything in one stop.

      We have all the Thermostats in stock and can ship today: https://kc.warmyourfloor.com/thermostats/floor-heating.html

  • I am installing heated floor system on concrete slab with DITRA Heat uncoupling in four rooms on first level. Each room has electrical cabling in place… 2 pole, 240V, 20AMP circuits for each room using what appears to be 12 AWG cable. Each space will have approx 120 – 160 sq ft of heated space. Preference is to go the 240V but my concern is the existing 12AWG existing cabling okay to use?

    • matthew@warmyourfloor.com says:

      Hi Alan,

      Local codes sometimes over-ride general guidelines so you may want to double-check.

      We stock all the Ditra Heat membranes (Both the standard and the insulated DUO) AND all the cables and thermostats as well.

      A dhehk240167 (heats 167 SF) cable draws 8.8 amps at 240v; since your max size room is 160 SF, this shows you a max value.

      While Schluter Ditra Heat does not publish electrical requirements, we know your 12 AWG wiring for this load will work fine.

      Give us a call or email, and we’ll be glad to put together some pricing for you!

    • matthew@warmyourfloor.com says:

      Hi David,

      A 100 sq ft cable at 240V would draw only 5amps by itself.

      Now it is recommended the floor heat be on a dedicated circuit.

      But if you have a circuit that can handle the 5 amp draw from the floor heat, along with the dryer, then you can have this on one shared circuit.

      You just want to make sure you’re not overloading the circuit when everything is powered on or the GFI in the thermostat will cut power to the system.

  • I’ve run into an existing system that is prewired but not made up in the electrical panel. Is there a way to determine the voltage rating of the installed mats from the load-side wires in the junction box? THANKS!

    • matthew@warmyourfloor.com says:

      Daniel,

      The heating element has a power lead that goes from the floor, up the wall to the thermostat location.

      That power lead always has a tag on it that indicates what voltage the product is.

      If you can’t access that power lead in the wall, you should contact an electrician to see if they can tell you the voltage of the product.

  • Hi I have issue I have floors 19sq m (220w for 1sq m) I used 16A thermostat ( witch I use 230V power) and I burned I know now I have used 20A thermostat my question is can I still used 230V power or I have to bring bigger power then 230V? Thanks

    • matthew@warmyourfloor.com says:

      Augustinas,

      The voltage of your power must match the voltage of the heating element in the floor.

      So if you have a 240V heating element, you need to supply it with 240V power.

  • Wes Huibregtse says:

    I have a 96 sq foot insulated porch that I want to heat using 3-30 inch X 10 foot Suntouch mats over the subfloor and under quickset and tile. I believe that a 15 amp 120 volt circuit dedicated circuit can handle this load. Correct?

    • matthew@warmyourfloor.com says:

      Hi Wes,

      The thermostat can not have more than 15 amps loaded onto it so you can never exceed that load.

      But yes, a 15 amp circuit would be able to handle that load as you would only be drawing 7.5 amps total between the three mats.

      But also keep in mind that if your porch is outdoors or exposed to the elements, you would need to use SunTouch’s outdoor product called ProMelt.

      That would change the electrical requirements for this project if your porch is outdoors.

  • matthew@warmyourfloor.com says:

    Hi John,

    My understanding is 240V does not require a neutral be present, you only need it for 120V.

    I always recommend consulting with an electrician though if you are unsure.

  • Can I use a wire for a 240V floor in place of the 120V wire?
    I purchased a new wire that should have been 120V but it is 240V.
    I waited almost 2 weeks and I cannot wait another 2 weeks

    • matthew@warmyourfloor.com says:

      Hi Greg,

      The power supply voltage must match the voltage of the heating element.

      So if you have a 240V circuit running to the thermostat, then you must use a 240V product, and vice versa.

      Supplying 240V power to a 120V cable will overload it. Supplying 120V power to a 240V cable will not be enough power to get hot.

  • Hi
    I am about to add a floor heating system to my bathroom. There is a baseboard heater already installed and I want to keep it. The area is under 150 sqft. My questions are first, what voltage should I get 120v or 240v if the existing baseboard is on 240V? Second, can I use 1 thermostat for both baseboard heater and floor heating system or each has to have its own thermostat?

    • Hi Reza,

      You’ll need a separate thermostat for the baseboard heater and floor heating system.

      And it is recommended that the floor heating system have its own dedicated circuit separate from the baseboard heater.

      Because of this, we would recommend that you use 120V power for the floor heating system since you’re under 150 square feet.

  • I want to use my existing 120v tying in at a light switch….how do I figure out how many amps are already on the circuit?…thanks so much for your help…
    Also I was told that I dont need the mat under the entire floor that the marble that I’m installing will pick up the heat and radiate it to rest of tiles…floor is 52″x170″….was thinking 18-30″×120″…this should be suffieient???….esp since there will be rugs in front of the sinks anyway…its a long narrow room with tub on one side and double sink vanity on other…thanks again for your help…how long to receive if I order your mats??

    • matthew@warmyourfloor.com says:

      Hi Terri,

      You would need to ask an electrician to evaluate how many amps are already loaded onto the existing circuit.

      As for that heated area, we always tell our customers you will only get heat where the heating element is located.

      The heat will only radiate about an inch away from the heating element itself.

      If you order a stock product we can get it to you in 5 days or less.

    • Hi Ren,

      The math for this will be around 1amp per 10 square feet for a 120V system. For a 240V system, it will be around .5amp per 10 square feet. This means that 1,500 square feet will be roughly 150amps for 120V and 75amps for 240V.

  • Alice B Rudolph says:

    My main breaker switch has 200 stamped on it, and the dedicated breaker is labeled as 20, my floor space is 70 square feet. Should I buy a 120 or 240 wire for my radiant heat?

    • Hi Alice,

      Since the dedicated breaker is 20 amps, you can use a 120V wire for the 70 square feet. This will use around 7 amps, and the thermostat will allow up to 15 amps. Feel free to give us a call if you have any further questions! You can reach us at 866-558-3369.

      Warm Regards,
      Warm Your Floor Team

    • Hi Michael,

      That is a very good question. Installing a foil radiant barrier under the floor heating mats won’t make too much of a difference. The products that we carry do a great job at heating the floor, regardless of what is underneath. This would be more of a personal preference, but it is not necessary.

      If you do decide to place the foil underneath, make sure that you get in contact with the foil manufacturer to verify that it would be compatible with a floor heating system. Feel free to give us a call if you have any further questions regarding this at 866-558-3369. Thanks, Michael!

      Warm Regards,
      Warm Your Floor Team

  • Tim Dickinson says:

    I want to use a 20amp circuit that is dedicated for my bathroom which will only have lights, fan, and an outlet. Can I put the heater on this same circuit?

    • Hi Tim,

      This will depend on the size of the bathroom. We always recommend using a dedicated 20amp circuit for our floor heating systems to cover the max 15amps that the thermostat can handle. However, if the square footage is smaller, the system might only draw a small amount of amps. This could potentially allow more items to be placed on that circuit, such as the lights and a fan. We suggest that you try to figure out how many amps are currently running on your existing circuit and check our product page details for the amount of amps for the type and size of floor heating system you want. If the total amount is under the 20amp max, you should be able to run the system.

      We encourage that you contact us regarding this so we can try and help you figure out if this will be possible. Please, give us a call at 866-558-3369 or email us at customercare@warmyourfloor.com and we will help you further. Thanks, Tim!

      Warm Regards,
      Warm Your Floor Team

    • Hi Pat,

      Yes, our systems require GFCI protection. However, all of the thermostats that we carry contain built-in GFCI for safety purposes, so you will not have to worry about any further steps. Please, feel free to contact us at 866-558-3369 if you have any further questions!

      Warm Regards,
      Warm Your Floor Team

  • Hi,
    I am redoing an existing bathroom in my basement. Concrete floor, 6′ x 7′ room excluding shower stall outside of that area. I am gutting the room. There is presently an older 240V baseboard heater. Since it is already there, I’d like to use the 240V for the floor heat but it is a very small room – would I be better to convert it to 120V? From what I read above you’d recommend 120V for new install due to small room size but this wiring is already in place. Also, can I reuse the same wall mount thermostat for the old baseboard heater for the new floor heat – my guess is no as there is likely a thermocouple I need to route for thermostat signal, yes? Thanks for your consideration.

    • Hi Ron,

      Yes, you can use the existing 240V wiring for your floor heating system. While we do recommend using 120V if the heated area is 150 square feet or less, there is no real advantage or disadvantage to using 240V since both voltages produce the same heat output. We recommend using 240V for areas between 151 – 300 square feet because 240V systems draw half the amps that a 120V system does, therefore you can heat a larger area without exceeding the maximum 15 amp capacity the thermostat can handle.

      If you already have an existing dedicated circuit at 240V, there is no reason to convert it to a 120V if you don’t mind using the extra break space in your panel. If you think you may need that additional breaker spot, that would be the main reason to convert to a 120V circuit. Otherwise go ahead and keep the 240V circuit you have, and just make sure to purchase a 240V heating element.

      Feel free to contact us at 866-558-3369 if you have any further questions. Thank you!

      Warm Regards,
      Warm Your Floor Team

    • Hi Bill,

      We offer SunTouch UnderFloor Retrofit Mats and QuietWarmth Retrofit Mats. Both of these should work for the width, but we only have 4′ and 6′ for the SunTouch mats. However, we do carry a 16″ x 5′ QuietWarmth mat that you can check out. Here is the link for this mat: QuietWarmth Retrofit 16″ x 5′ 120V

      Feel free to call us at 866-558-3369 and we will be able to help you determine the best option for your space and flooring. Thank you!

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