Electric In-Floor Heating

A simple way to warm your feet.

Written and Photos By Steve Maxwell

If you’ve given up on radiant in-floor heating because of the difficulty and expense of installing a full-blown system of pipes, pumps and hydronic control equipment, back up a bit. There’s a DIY-friendly way to warm your place from the floors up, and it makes a lot of sense in a surprising number of situations.

Radiant in-floor heating was first made popular with hydronic systems that circulate warm liquid through pipes set in the floor. Today this technology is mature, efficient and ideal for full-size homes, especially those under construction. When the amount of heat required justifies the cost of a boiler and related equipment, hydronic systems are among the most economical and comfortable ways to heat a home or year-round cottage.

But not all building situations fit this description. If your place is small or seasonal, the fixed cost of installing the equipment to heat the liquid, pump it through floor piping and control temperatures in different parts of a building start to look pretty daunting. Who wants to spend $8,000 to $10,000 on hydronic equipment when a small, well-insulated structure might only consume $300 or $400 a year in energy? Or what about existing structures where only certain rooms require additional heat? Then there are those older floors that aren’t easily retrofitted to accept heating pipes or to transmit warmth effectively upwards to the rooms above. Scenarios like these introduce the kind of technical complications that cause some people to give up unnecessarily on the advantages of in-floor heating, even though an excellent alternative to hydronics exists. Canadians are at the leading edge of this nimble technology.

Electric in-floor heating mats are made of a non-woven fabric surrounding high-resistance heating wires embedded right into the material. The result looks sort of like an electric blanket. And while installing the system isn’t as easy as making your bed, it’s not difficult once you understand the details involved. There are five main steps to a typical installation: determine the heating mats required for your situation, unroll sections of electric heating mat, test the electrical performance of the installation before and during work, put finished flooring on top, and then complete the electrical supply and thermostat connections.

The system installed in the photos is made by B.C.-based Nuheat. Each heating mat is either one of a specific number of standard sizes or custom sized at the factory for specific situations. Neither is designed to be cut on site because the embedded wires can’t be trimmed. This is why every mat installation begins with a measured floor plan of the areas involved. Your plan needs to show those places that require heating mats, plus zones occupied by kitchen islands, cabinets, toilets, showers and stairs that don’t need heating. You must also choose either a 120- or 220-volt electrical supply for your system. Different mats are also required for use under wood-based flooring versus ceramic or stone tiles. As you work, decide where the electrical feed and thermostat will go. This determines where the lead-in wires are located on each mat and how they’re routed. Try your best to locate lead-ins in areas with the lowest amount of foot traffic.

Mats are shipped in boxes, but they’re not ready for use right away. First they need to be tested and verified. Immediately after each mat is manufactured, electrical measurements are taken, with results recorded by technicians on a unique tag that remains visible in the power supply box that feeds the system. Since the heating mats themselves remain inaccessible after installation, you must use a multimeter to prove each one survived the transportation and handling process without damage. It’s prudent to repeat this electrical testing before, during and after installation. It takes just a few minutes, and it’s critical.

You’ll need a digital multimeter to determine the electrical integrity of each mat in two different ways. Start by assessing the effectiveness of the internal wire insulation on each mat by measuring electrical resistance between the ground wire and each of the two power supply wires independently. If the insulation is good, you’ll get an open circuit reading. You want to see resistance that’s too high to measure.

The second electrical test determines if the internal resistance of the heating cables themselves is correct. Use your multimeter again to measure resistance between white and black power wires. If all is good, the ohms reading you get will match the reading on the specs tag closely – up to five per cent less than factory figures are okay, or up to 10 per cent more.

Discrepancies are rare, but you need to discover them before the mat goes down and gets covered by flooring. Repeat this pair of electrical tests (one for insulation integrity and the other for proper internal resistance) after each major installation step. If damage has occurred, knowing about it right away makes it easier to see the location and cause.

With the integrity of the mats proven initially, unroll each one where it’s supposed to go, and then tape the edges of the adjoining mat together to hold them in place. Just be careful as you work. The mat is too fragile to walk on safely without some kind of protection. Sheets of clean plywood work well as a temporary walkway. Also, understand that heating mats are designed to be installed on top of the kind of underlay used below laminates or other flooring. If you’re working with ceramics or stone tiles, heating mats go over top of the substrate, anchored there by a coat of acrylic/latex thinset. After this has dried, set your tiles in more thinset troweled directly on top of the heating mat.

Install your finished flooring on top of the heating mats, arrange the wiring and thermostat connections made to a GFCI-protected electrical supply, then dial up the heat. Electric in-floor heating technology rounds out the options for a nation of people dealing with life in a cold country. It’s the simplest way to heat small spaces from the bottom up, and your feet will be the first to let you know how good this is.