Everything You Need to Know about Heating Concrete Floors

Hello, thank you for joining us. My name is Lynn, and I am a customer service representative here at WarmlyYours. Today, I am joined by Scott. Hi everybody! Today, we're going to be discussing everything you need to know about heating concrete floors. If you have any questions during today's presentation, please feel free to ask. You can do so either at the bottom of the screen in the "Ask a Question" tab or in the sidebar chat. Either way, we'll see it and address it, if not right away, then by the end of the presentation.

So, Scott, can you tell us a little bit about what we will be covering today? We're going to take a look at slab floor heating, discuss a project example, and then go over how it's installed. We have broken it up into three main topics for today. Let's start by talking about the benefits of radiant flooring systems.

Absolutely! Our radiant heating systems are all electrically based, utilizing electrical cables to warm the surfaces they are embedded in. This system effectively warms the floor from the ground up, ensuring even heat distribution throughout the entire room. When embedding these systems into concrete slabs, the space can become significantly warmer than would be achievable with a traditional HVAC system.

Concrete slabs, especially in the Midwest, are commonly found in basements, which are notoriously cold. In many cases, the air ducts are overhead, causing hot air to blow down and rise back up to the ceiling, leaving your feet cold while your head feels warm. The advantage of radiant heating is that it fills the entire room from the floor up, providing a completely different and more comfortable experience, especially in basements during winter.

Can you explain how to warm a room that has an existing slab? When working with a concrete slab, the first question we ask is whether you are pouring a brand new slab or heating an existing one. If you are heating an existing slab, you will want to apply a very thin layer on top and isolate the top surface from the concrete slab. There are two ways to heat floors: you can either heat the entire slab or just the thinner layer on top. It's essential to isolate the heat from the slab itself to ensure that you are only heating the thinset or self-leveling layer and the flooring above it.

To achieve this, we recommend using Sika's Orb, which is made from synthetic or natural cork. This material has an R-value that helps push the heat upward, preventing it from sinking into the slab. Traditionally, people relied on hot water systems, which take longer to heat the entire concrete slab. Heating just the layer on top allows for faster heating times and warmer temperatures. It's crucial to determine whether you want to heat the entire slab or just the top layer, as this will influence the equipment we recommend for your project.

When installing a new slab, especially if you're building a new home or an addition, this is an excellent option. If the finished concrete floor will be the final surface, such as polished or stamped concrete, embedding the cables in the slab is typically necessary. The cables used are about five watts per linear foot, providing up to 20 watts per square foot, ensuring sufficient power to heat the slab and the surrounding room effectively.

Now, let's discuss expansion joints and how they factor into the installation. We never run cables through expansion joints; instead, we stop before reaching them. It's essential to know where these joints are located when you send us a drawing of your space. If you have an expansion joint running through the middle of your floor, you will heat one monolithic slab on one side and another on the opposite side. Expansion joints allow for differential expansion and contraction, so we heat them individually.

We have a question here already, which I think is a record for the fastest question on one of our webinars. Annie asks about a remodeling job where there's a new concrete slab and an old existing slab. In this case, you want to use one consistent type of heating. If you have an existing slab, you cannot embed cables in it, so you will heat that slab from the top. If the area is large and includes both old and new slabs, you should heat them in the same manner to ensure they maintain a consistent temperature.

Moving on, when discussing warming up a new slab with flooring, if it's a new slab, you'll want to use cables spaced at about five inches apart, as per the older electric code. The National Electric Code previously limited wattage to 15 watts per square foot with flooring on top and 20 watts per square foot without flooring. However, the 2017 version of the code eliminated these maximum wattage requirements. It's crucial to check with your local building inspector or authority having jurisdiction to confirm any local limits on watt density per square foot.

The actual slab heating system can come in two types: cables and mats, or rolls, which have the cable attached to a mesh. These systems can provide about 20 watts per square foot for heating, compared to the standard floor heating systems that offer 15 watts per square foot. The choice between cable and mats depends on the specifics of your installation. Cables offer flexibility for oddly shaped rooms and may be more economical, while mats provide quicker installation.

When using rolls with mesh, it's important to inform your concrete professional to use sub-three-quarter-inch aggregate. This ensures that the concrete flows properly through the mesh, preventing a thin layer of concrete with larger rocks on top.

We love cross-sections here at WarmlyYours, as they illustrate how to lay out the cable within the slab. You would start with compressed crushed rock, followed by polystyrene insulation, then pour two to three inches of concrete as the bottom layer, placing rebar on top with the cables zip-tied to it. Finally, you would pour another two to three inches of concrete as the top layer. This two-stage installation method tends to be slower, so be prepared with plenty of tie wraps if you're using cables, as they require more fastening than the mat system.

It's essential to ensure that the cable is positioned correctly within the concrete. It should not sit at the bottom of the slab but rather be placed in the middle of the pour. When installing the product, avoid stepping on factory splices, as these are critical points where the heating wire connects. To keep track of these splices during the concrete pour, use construction flags to mark their locations, allowing you to avoid stepping on them.

Let's take a look at an example project installed in Crystal Lake, which features a polished concrete floor in a walkout basement. They utilized our SmartPlan service, which provides a complimentary installation plan based on your layout. By sending us your dimensions or a hand-drawn sketch, we can return a SmartPlan that outlines how to install the mat and where to cut and turn it.

The SmartPlan indicates the start and end points of the mesh layout, making it easier to follow during installation. I personally installed a similar project on a hot July weekend, and it was quite the experience! It's crucial to remember that you should never heat under permanent fixtures like bars or wine racks; instead, design around them.

Once we have your dimensions, we can quickly provide a plan, often within a day or two. This efficiency helps avoid the confusion that can arise when trying to figure it out on your own. The installation plan will detail the layout, including the power modules that control the system.

The total area of the basement in our example was 885 square feet, with 737 square feet heated. The wattage was 13,410 watts, requiring a total amperage of 56 amps, which is why multiple power modules were necessary. It's important to use dedicated non-GFI breakers for these systems to avoid nuisance tripping, which can occur if both the thermostat and circuit breaker have GFI protection.

The heated area will often differ from the total area due to the exclusion of permanent fixtures and the need to leave some space near the walls unheated. This design choice reduces upfront costs and operational expenses since you're not heating unnecessary square footage.

Now, regarding costs, many people assume electric floor heating is expensive, but it's quite the opposite. For the heated area of 737 square feet, it would only cost about 61 cents per hour to run. If you use the basement for eight hours a day, it would amount to roughly $4.87 per day. If you only use it occasionally, the annual cost can be minimal.

When testing the system, you need a digital ohmmeter, a circuit check, and a mega ohmmeter. The mega ohmmeter tests for insulation integrity, ensuring there are no shorts or leakage. It's crucial to test the product upon receipt and before installation to catch any issues early.

As you begin your installation, ensure your concrete installer spreads and tamps 8 to 12 inches of crushed rock, followed by 2 inches of polystyrene insulation. The rebar used in the installation must be positioned correctly to keep the heating cables in the middle of the pour.

Expansion joints should be marked clearly, and no cables should be run through them. If you have a mix of old and new slabs, ensure both are heated consistently from the top.

During installation, make sure to install the thermostat sensor wire properly, centering it between two runs of cable and placing it in a capped conduit to protect it from concrete. Once everything is laid out, you can begin pouring the final layer of concrete, ensuring it measures between four to six inches, with only two to three inches above the heating cables.

The thermostats used for these systems are similar to those for other floor heating applications and come with a floor heating sensor. For larger areas, power modules will be necessary to manage the load. Each thermostat can handle 15 amps, so it's essential to ensure you're sending the correct voltage to the thermostat.

The finished project showcases a beautiful polished concrete floor, demonstrating the effectiveness of the embedded heating system. The total cost for this project was $5,720, which included various heating mats and a Wi-Fi thermostat for easy control.

Electric heating systems typically outlast the flooring they are installed under, providing long-term reliability. If you have any further questions, please feel free to ask.

We have a couple of questions that came in ahead of time. Tara asks if it matters if the concrete slab has tension rods in it. Generally, rebar is required in concrete installations, and it serves as a critical anchoring point for the heating product.

Annie asks whether an existing concrete floor needs to be removed to pour a new slab. As we discussed earlier, if you have an existing slab, you will heat it from the top.

Annie also inquires about the pros and cons of water versus electric heating and whether earthquake cracks impact the heating mechanism. Electric systems are generally more reliable, as they maintain consistent temperatures without the risk of cooling down along the run, which can occur with hot water systems.

If you have any additional questions, please don't hesitate to ask. Our next webinar will be on October 14th at 1:00 p.m. Central, focusing on tips from the pros for planning and installing your floor heating system.

We also offer daily training sessions on Crowdcast, covering various topics and answering any questions you may have. Additionally, we have a September promotion offering 20% off Environn EZ-Mats, designed for use under carpet and laminate flooring.

After this webinar, you'll receive an email requesting feedback about your experience. We appreciate your comments and suggestions for future topics. If you have any questions, feel free to reach out to us via email or call.

Thank you for joining us today! I hope you found the information helpful, and as always, stay warm and be radiant.