Radiant floor heating is the most comfortable way to heat a space. Period. I love it and so do my customers and the builders and remodelers who increasingly demand it. Since radiant systems heat objects (not the air, like conventional systems), they're fuel-efficient, quiet, clean, and comfortable, all while eliminating baseboards and radiators.

However, some contractors balk at radiant heating due to the lack of easy-to-install systems, especially in retrofit applications. So how can you serve your customers (and your business) when they request radiant for a new kitchen, addition, or bath but will use existing HVAC for the rest of their house? For my clients, using the right system with good manufacturer support helps them achieve their goals while helping with their bottom line.

The Right System

I've installed just about every kind of radiant system there is. For retrofit applications and some new construction, I use the Watts Radiant SubRay hydronic subfloor system. It heats with water–which delivers the best heat–rather than electric mats (which I've found are most sensible for installations of less than 200 square feet). Once the heat-loss and design calculation is done (more on that later), you or your carpenters can install the bulk of the system, which is mostly birch plywood components and plastic tubing, as opposed to pouring and placing of concrete typically associated with hydronic tubes. This helps control the schedule and limit the number of subs you need.

The Right Design

Photo: Courtesy Watts Radiant The tubing lies loose between sleepers. The header blocks snap it securely in place.

A successful radiant installation begins with a heat loss and design calculation. While the manufacturer offers software that will calculate heat load, specify required supply temperatures, and build a parts list, and there are calculation guidelines in the product literature, the key to consistent success is working with your dealer or with the company directly; they know the ins and outs and will draw up good, dependable calculations.

The heat loss calculation determines the amount of heat the system must deliver to maintain a comfortable temperature, ideally delivering a consistent indoor temperature of 70 degrees Fahrenheit on the coldest design day. The calculation is adjustable to provide warmer temperatures, however. I spec 72 degrees for elderly or less active customers. I involve customers in system design, which helps me learn about any not-so-obvious temperature requirements. Rooms with high ceilings or lots of glass will have an impact on heat loss calculations and may require supplemental heat. Guidelines from the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) suggest floor surfaces not exceed 85 degrees Fahrenheit or 35 BTUs per square foot. If the room or space cannot be sufficiently heated within this constraint, the heat loss calculation calls for supplemental heat.

The Right Installation

Photo: Courtesy Watts Radiant The aluminum conductive roll placed over the sleepers helps transfer heat to the finished floor.

Sleepers and Header Strips. Start with a clean, dry, properly framed and fastened subfloor. Joist bays should be insulated to protect from downward heat loss. Next, lay out the SubRay sleepers and header strips. If the room is oddly shaped or way out of square, snap lines. Edge pieces may have to be ripped to fit. I dry-fit the first few sections to make sure I'm on layout before fastening with an autofeed screwgun.

Tape and Tube. Next, install reflective tape between the sleepers. Then, unroll the tubing into the space between the sleepers and snap the tubing into the header strips, which hold it securely. Next, install the aluminum conductive roll over the sleepers. It covers the tubing, so be careful nailing.

Finally, I like to pressure-test all tubing (and keep it under pressure) during final floor installation. If someone pops a nail or screw through it, the hiss tells you a repair is needed (repair couplings are available).

Floor Types. Install cementitious backer over the sleepers before installing tile, marble, granite, or brick pavers, all of which are great over radiant floors. For floating floors, carpet, or sheet goods, use SubRay channel covers to support the proper underlayment before laying the floor.

Strip hardwoods are best installed perpendicular to the SubRay sleepers, an important consideration at layout. And, since wood is affected by humidity and temperature changes more than other flooring products, check with your flooring supplier for which species and installations work best with radiant heat. If required, SubRay offers optional metal channels to allow parallel wood installations, but this requires gluing the wood.