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PEX tubing on sand underlayment before paver installation on a Minn. driveway.
Photo courtesy of Architect Mechanical, Inc.
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By Marcia Jedd
Taking a cue from the indoor home setting, where radiant heating systems have been used for decades, the great outdoors is warming up, too. Radiant heat warms the floor and any object in contact with the floor to distribute an even, no-draft heat. In the outdoor setting, antifreeze is circulated through flexible hydronic piping, heating surface temperatures to 38? to 40? F and averting the need to remove pesky ice and snow. Plus, the environment is spared from salt and chemicals.
Warming a Minnesota driveway
Especially in colder parts of the country, there's a need for heated walkways, driveways and patios. Consider the case of a home in Minneapolis-St. Paul, Minn. A 200-foot long driveway on a partially shaded incline was difficult to plow due to the placement of the driveway, making it an excellent candidate for a radiant-heating snowmelt system to allow the medical professional living in the home safe and easy access during winter.
M.A. Peterson Design Build Inc. (Edina, Minn.) offered the solution as part of a major home remodeling that also involved replacing old walkways and the driveway with granite aggregate-coated pavers. Underneath the pavers is a high-tech radiant heating system to automatically melt snow and ice.
Rick Tesch, landscape designer for M.A. Peterson, explains that cross-linked polyethylene (PEX) tubing was installed underneath the pavers to provide the structure for distributing the liquid glycol. Highly durable PEX tubing handles high temperatures and extreme temperature changes, as well as weight and compressive forces.
Pat Niccum, president of Architect Mechanical, Inc. ( www.architectmechanical.com], a heating, ventilating and air conditioning firm in New Brighton, Minn., designed and installed the outdoor heating system. He explains that the glycol's run through the tubing is controlled by a separate boiler system with manual or automatic controls. The result is the ability to melt snow and ice on pavers at the touch of a button. In this particular system, a moisture and temperature sensor sends information to the boiler's control system.
Electric cables are another option to heat walkways and driveways but, in the long run, are often costlier due to energy costs, Pat says.
Tips to the trade
Pat explains the best opportunity for installing an outdoor heating system is on new construction when the HVAC plan can be designed and integrated with the home's automation-control systems—even tied into lighting systems when appropriate. Remodeling and major outdoor landscaping projects are also perfect opportunities to install an outdoor heat system.
"With remodeling, there has to be a relationship between the general contractor, the heating contractor and the driveway installer as to what method is used for installation," Pat says. "Plan early!"
He emphasizes heating systems must be planned with the appropriate pumping system for the glycol. Additionally, while the tubing can be embedded in concrete, other materials such as asphalt require a barrier between the tubing and the material so the tubing isn’t damaged.
Such complexities mean that general contractors must seek thorough training or to hire a subcontractor with HVAC and plumbing expertise. Pat cautions anyone installing these systems to understand what they're dealing with when it comes to installation methods, boiler capacity and system controls.
"Definitely seek out manuals from the manufacturers such as the PEX tubing maker for specific installation instructions," Pat says.
The strain of heating surfaces in the great outdoors means high energy loads are put on boiler systems. Pat says a considerably higher BTU load is required for the outdoor environment compared with interior settings. These allocations vary by region of the country depending on weather conditions. In the upper Midwest, for example, Architect Mechanical uses a guideline of 150 BTUs per square foot input. In the case of the 200-foot driveway in the M.A. Peterson project, the 800,000 BTU load input required two boilers to support the project.
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