Concrete-Free In-Floor Heating

Everyone I know likes warm feet when it’s cold outside, and that’s the attraction of radiant in-floor heating. You can’t beat it for even, efficient distribution of warmth in any building, but there’s a problem. Too few homeowners understand that radiant systems can be installed in wood-framed floors, too. You don’t need to pour a brand new, pipe-embedded concrete slab to enjoy warm floors and happy feet. While this standard option is an excellent and widely applied choice, it’s not the only one. In fact, radiant in-floor heating is possible in almost every type of renovation and new construction project. This is what you’ll learn about here.

The first thing to understand is that there are two types of in-floor systems. The most common uses pipes to carry warm water through the floor structure. This is called a hydronic system and it turns the entire floor of your home into one big heating radiator.

Another completely different option includes thermostatically controlled, high-resistance electric heating grids or mats embedded in floors. Think of it like an electric blanket installed under your feet. Both systems have strengths and weaknesses that you need to know about before you can make an informed decision.

The Electric In-Floor Option

When it comes to making your floors warm, electric mat systems are certainly the most mechanically simple option. The heating grid itself can be installed under ceramic tiles, laminates and engineered wood products. Put it down correctly and the installation adds only 1/8” to overall floor height. The best systems are even simple enough to be installed by do-it-yourselfers. Add a wall-mounted thermostat, then take off your socks in February and smile.

So why would anyone choose hydronic in-floor heating when electrics are so simple? Operational cost is one reason. Depending on market conditions, electricity can be the most expensive form of home energy going. It’s also completely dependent on grid-supplied electricity. Where even a small portable generator is big enough to power an oil or propane-fired boiler in case of emergency, not so with an all-electric system. That said, electric floor-warming systems really shine for single room applications and renovations. They’re outstanding as part of a solution for the widespread misery of all those cold, garage-top bedrooms found in modern subdivisions across Canada, too.

Hydronics in Wood-Framed Floors

Hydronic in-floor heating systems make the most sense in applications that involve large areas of your house. That’s because pipes in the floor are only part of the equation. You also need to consider an appliance to heat the liquid flowing through those pipes, and a control panel to regulate the flow thermostatically. And while none of this makes sense for just a bathroom or den, it’s quite practical for a large portion of your home. This is where hydronics shine.

There are three ways to install a network of in-floor hydronic heating pipes in a wood-framed floor. You can fasten them to the underside of the subfloor from below. Easy, yes, but heat transfer upwards to the floor surface isn’t terrific. You can also embed hydronic pipes within self-leveling concrete poured directly on top of a wood floor. Thermal performance is excellent, but the work is troublesome, messy, expensive and reduces ceiling height more than any other approach.

Of the three options for installing hydronic pipes, casting them into a slab-on-grade is best, but it’s only possible with new construction. There are two things to understand when plumbing a new slab like this with hydronic pipes: the need for under-slab insulation, and the importance of adequate site drainage. Both affect the performance of your system in big ways.

The rule of thumb in the hydronics industry is that under-slab insulation levels should be five times as great as the insulation value of the floor above the pipe network. Since a typical floor might have R-2 above the pipes (considering concrete and finished floor coverings), this translates to an R-10 layer required under the slab. Two inches of extruded polystyrene foam (the pink or blue stuff) gives you that. Another under-slab option is radiant bubble barrier foil. One Canadian product is called rFoil (888-313-3258; www.tvmi.com). It inhibits heat transfer by radiation, a factor that's often ignored in energy efficiency calculations. Regardless of what you use, insulation layers need to wrap around the sides of any concrete slab, breaking the thermal path that would otherwise let heat escape by conduction through the edges, into the foundation wall.

Radiant in-floor heating can be added to conventional homes during renovation, too, and the most effective option for pipe installation in this case involves setting the network in a 1 1/2-inch thick layer of fibre-reinforced concrete. This is a great option for use under a new ceramic tile floor.

Mounting radiant heating pipes underneath a wooden subfloor is an option, but it’s the least attractive one. There are two drawbacks you should know about. First, since the pipes aren’t an integral part of a high-mass floor, the transfer of heat to the house occurs more by convection than radiation. As a result, it becomes necessary to install underfloor insulation as part of the job. This traps heat and directs it upwards in a way that’s not necessary with a concrete-on-wood installation. Also, because the pipes and plates that fasten to the underside of a wooden subfloor aren’t firmly encased, they’re free to move as they heat up and cool down. This leads to noise that would otherwise be completely absent in a concrete-based installation.

An excellent compromise between these two options involves setting heating pipes within grooves created in the top of the floor. You can do this by laying down 10” or 12”-wide strips of 3/4” plywood, with a 3/4” gap between neighbouring strips to create a pipe groove. Set reflective foil insulation in the gap to direct heat upwards, then lay pipes in the grooves and install a finished floor on top. Some manufacturers offer molded plastic grid systems for use in place of the plywood strips.

Radiant in-floor heating is fast-becoming a must-have home feature. That’s because it boosts home wintertime comfort levels more than anything else. The good news is that even those of us who don’t live on a slab of concrete can now enjoy the warmth.

Hydronic in-floor heating is now a mature, reliable technology that’s being used in commercial and residential applications all over Canada. And the fact that you can count on it is just one more example of a fascinating trend in the homebuilding world. As synthetic materials get better, and resulting improvements are applied to wider areas of use, brand new possibilities emerge. Who would have thought a new kind of super-tough pipe would end up making a whole bunch of Canadian feet warmer each winter?

Understand Your Heating Costs

You won’t spend long researching radiant floor-warming systems before you discover tall statements like ‘costs just pennies to operate’ or ‘heat your bathroom for less than 10 cents a day’. As good as radiant heating systems are, they’re not magic. They don’t have the ability to transcend the laws of thermodynamics, so beware.

The fact is, all floor-warming systems simply deliver heat. They don’t make energy. Ultimately, the cost of heating your home is dependent on two things: the rate at which your home loses heat, and the cost of the energy delivered to your house and the efficiency of that delivery process. While it’s true that having a warm floor makes you feel more comfortable at somewhat lower room temperatures, don’t expect massive cost savings as a result of any in-floor heating investment.

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