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phc december 2011


| FROM THE FIELD | CONTINUED FROM PAGE 64 tubing in place, especially when it is cold out and the tubing is stiff. We try to get a loop (two passes) in the tread and a pass of tubing in the vertical riser. It is hard to get tubing close to the leading edge of the step where ice will accumulate. My friend and fellow columnist, John Abularrage came up with a brilliant innovation where he ran Multi-Cor PEX vertically down the steps and formed the bends such that the entire step was covered (See photo 1). Boilers. If at all possible, find an indoor location to

mount the boiler(s) and pumps. I realize that mechanical space is at a premium. Three of my snowmelt projects have outdoor boilers. I was out on one last year during blizzard conditions. It was dark, cold and snowing sideways. I was lying in a snowbank with a mini Mag-Lite clenched in my teeth trying to read a wiring diagram. This is no way to work on a boiler. We have one current

experiment, I turned the system pump off until the boiler cycled off on limit, 155 F in this case. I then turned on the system pump to see what would happen. Within seconds, the boiler temperature dropped enough to kick on the burner. In less than a minute, the boiler temperature was the same as the initial start-up temperature, with no temperature change in the slab. I can sum up my experience thusly: I want as much

heat as possible to flow into the slab as quickly as possible. I have no interest in maximizing efficiency or “saving” energy (there is nothing to “save”). My only goal is to make the snow or ice disappear as fast as possible. With dedicated condensing equipment, it makes no sense to try to temper the supply water temperature. Controls. Almost all of our systems have a snow/ice

sensor tied to an operating control. This will automatically activate the system when snow or ice is present. It will also have a slab sensor to turn off the system when the slab is up to temperature, typically 38- 40 F. We also incorporate a “manual on” switch to manually activate the system in the event of a sensor failure or to preheat the slab in advance of an oncoming storm. We use a 12-hour spring wound timer switch to avoid the astronomic fuel bills caused by a system that was accidentally left on (Yes, this has happened to me). I also incorporate a “manual off” or disable switch to kill the entire system if the owner does not want it to operate. A simple three-way toggle switch with “off-auto-on” points would serve the same purpose. The snow/ice sensors have proven to be the Achilles

project in progress with an outdoor boiler, but this will be our last. I’m getting too old for this! In all but the smallest jobs, we have a dedicated

snowmelt boiler or boilers. Except for the outdoor boilers, we only use condensing boilers for snowmelt. This eliminates the thermal shock and condensing issues that have to be addressed with non-condensing equipment. Condensing boilers thrive on the low return water temperatures and will operate at peak efficiency in snowmelt applications. This leads to the issue of “thermally shocking” a

snowmelt slab. I imagine that in certain commercial applications, with industrial horsepower boilers and pumps, it is possible. In a residential application with a properly sized boiler, it is all but impossible. It just is not possible to raise the slab temperature fast enough to thermally shock it. The system quickly establishes equilibrium and the temperature rises very slowly. For example, last winter we installed a system in a

1,400-sq.-ft. residential driveway. The ¾" tubing was installed in a 4" base slab of concrete on 9" centers. Granite cobblestones where then laid into a mortar setting bed. The entire structure was about 10" to 12" thick. I roughly calculated the entire mass at over 100 tons. This mass is a black hole to Btu. With a properly sized boiler and pump, it just is not possible to change the temperature quickly enough to cause thermal shock. On this job, we installed a 250,000 Btu Triangle Tube

condensing boiler. It was piped through a hydraulic separator with a separate boiler and system pump. As an

heel of these control systems. We have seen an unacceptable failure rate of these sensors. One manufacturer had the audacity to inform me that the failure was caused by water getting into the sensor. Really? Memo to manufacturer: these sensors are installed OUTSIDE! We finally found a sensor that would hold up to the elements, made by Caleffi, only to find out it was discontinued. Just my luck. I would be curious to hear what my fellow contractors are using. We recently completed a system with a networked

control system (Uponor CCN). I call these control systems DDC-Lite. It gives you most of the functionality of a commercial DDC system at a fraction of the price. These controls allow remote access, activation and monitoring of the snowmelt system from your office or anywhere with Internet access. I can remotely activate the system in advance of a storm, monitor it to see if it is functioning properly and locate failure points before leaving the shop. A scaled-down version of this system designed specifically for snowmelt systems is on my wish list. If you are in the snow belt, snow/ice melt systems can

be a profitable niche. Design and install them right or you will regret ever taking the job. Done right, and priced accordingly, there is nothing more satisfying than driving by one of your snowmelt projects and seeing a clear, dry driveway, while the neighbors are breaking their backs shoveling their drives. l

Dan Foley is president and owner of Foley Mechanical

Inc., based in Lorton, Va. FMI specializes in radiant, hydronic and steam systems as well as mechanical systems for large custom homes. He can be reached at 703/339-8030 or at


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