My introduction into the art of leak detection in slab-based hydronic radiant heating systems was in our town's version of Levittown, called Fireside. They were slab-on-grade homes with 1/4-in. copper tubing embedded in concrete.

Back then, in 1972, homes in Fireside had radiant heating systems that were springing holes like a metal street sign sprayed with buck-shot! The first one I tagged along on as an apprentice was easy to find because it could be plainly heard below the thin concrete.

It began at a soldered coupling, and thermal stress had driven the tubing into the coupling, breaking the solder-joint. As the leak worsened, it had eroded a sink-hole in the earth almost large enough for me to crawl into!

Fireside's boilers were shoe-horned into the space below the stairs to the upper floor or, for single-floor homes, out in the open and looked like a stove without any burners.

The first time I encountered one of those stove-like boilers on a no-heat call, I walked right past it to look for one hidden in a closet. Not exactly a huge confidence builder when the homeowner has to point to what was hidden in plain sight. ("Excuse me ma'am, but I'm looking for your boiler." "You're standing beside it.")

Stop, Look, Listen
At the time, we used several methods for finding leaks. The first was to stop, look, and listen. Appliances were unplugged or turned off and the boiler disabled to keep the home library-quiet.

While walking through the home's rooms, you kept a keen eye on the lookout for damp spots and/or windows that were dripping-wet. If that yielded no clues, a return to the V-8 stuffed in the sub-compact engine compartment was in order to feel the outgoing 1/2-in. tubes between the manifold and floor, which were — of course — on the back side of the boiler. Getting to them included contortionist-like body positions best left to young apprentices.

The idea was to find out which lines were "hot" to the touch. The boilers held domestic coils and maintained temperature, so a hydronic system at rest would quickly reveal which circuit or circuits were affected.

In areas where ceramic tile or floor surface materials impervious to water-damage were installed, we would turn off the radiant heating system and close its manifold valves for a few hours — or a day, if the outdoor weather wasn't too cold — and return to wet-mop the area while turning on the radiant system.

Most Fireside homes didn't include outdoor reset or mixing strategies, as we do today, and the sudden influx of hot water would create what looked like an x-ray as the tubing would dry out the flooring directly over its pathway — magic! Leaks often appeared as a splotch of dried concrete, screaming out "dig here"!

We also used an old stethoscope-like stereo device with twin metal discs that you had to gently set down on the floor if you had the stethoscope ends in your ears, or else risk being deafened by the noise when they contacted the floor.

A door slammed or hard shoes stepping on concrete sounded like gunshots while the whine of a circulator or refrigerator motor could be clearly heard. For those of us with young knees, there was also an old-style, hand-crank-like phone device with a contact-pin sticking out its opposite end for direct contact with piping or the floor to listen for leaks.

Locate, repair, patch, or abandon — basically, those were the choices and many opted to cap-off lone circuits. If multiple circuits were involved, many chose to abandon the radiant heating and install baseboard. Almost all of the Fireside systems have long been abandoned — victims of thermal stress.

Of course, that was then — this is now!

Six Steps To Leak Detection
Today, we have much better ways of detecting leaks than just the old stop, look, and listen method. Consider these steps:

  1. Is there a leak? A hydrostatic pressure test will reveal if there is a leak and how quickly the system is losing water. Long-term leak detection can be monitored by installing a water meter.
  2. Isolation. If loops/manifolds are valved on both the supply/return, you can begin the process of elimination.
  3. As-built records. If the owners have an accurate as-built record for embedded tubing, you can narrow your search area considerably.
  4. Detection methods include:
    Stop, look, and listen is still the first option: windows dripping with condensation; pets seeking out a single specific warm spot; wet moldy areas; damp carpeting and noises — like a roiling boil as small stones are rattled against the underside of concrete, or a hissing spray-like sound. Use of oldstyle listening devices.
    Infrared thermometer: A handheld, point-n-shoot, inexpensive infrared heat detector and bare feet (ask permission first) can make for a great investigative combination. While the detector can "see" tubing heat-lines and larger areas where leaks may be present, your feet will often notice broader warmth zones. This is also a great way to find air-bound loops that aren't circulating.
    Ultrasonic leak detection: If you've ever purged a hydronic system by using a garden hose, you've probably learned to double-over the hose to regulate pressure during the process. Water escaping through the partially pinched-off hose crackles as air bubbles pass from high to low pressure and expand. Ultrasonic leak detectors listen for noises generated by air or gas you've introduced in the system as it escapes through a crack or pin-hole leak and expands. Expect to spend $800 to $1,500 for a detector.
    • Infrared thermal imaging cameras: If you've got about $30,000 you're not using and don't need, you can purchase one of these thermal imaging devices. If not, you might be able to rent or borrow one. They show temperature variations by color and different density/materials will sometimes appear in varying shades.
    • Gas detection: Helium and hydrogen detectors can be used if they're sensitive enough to measure ppm (parts per million) at, or below, 50 ppm. Above-50 ppm devices can work too, but they're said to be less precise. Evacuate the affected loop by forcibly ejecting the hydronic fluid (fill and purge with compressed nitrogen or air instead of simply using an air compressor to move the fluid). When filling with helium or hydrogen, be careful not to flood the area with gas or you'll contaminate the site.
    Low pressure rules the day! Start with a single low-pressure charge and don't continue to feed gas into the system. It takes time for the tiny molecules to seep up through concrete, but if you're patient, the results can be spot-on and location of minute leaks can be pinpointed.
  5. Repairs. There are some piping oddities awaiting your repair attention — unwanted and unpleasant surprises. What looks like copper at the manifold can turn out to be steel tubing below the floor that has a copper coating.
    The age and type of piping materials should be considered. Demolition and removal of floor coverings, concrete and potential for interference from utilities and plumbing may all contribute to the go/no-go repair decision.
  6. Restoration. Communication and a full understanding of the worksite responsibilities will ultimately define how satisfied a client will or will not be at completion.

Dave Yates is a Master Plumber who owns and operates F. W. Behler, Inc, a full service PHVAC firm located in York, PA. Yates is certified through the Radiant Panel Association as a hydronics designer, installer and instructor. To reach him, e-mail behler@blazenet.net