IN LAST MONTH’S column (pg. 18), we began looking into a typical below slab-on-grade leak.
The next step of sleuthing is to feel the inlets and outlets of all the baseboards to see if you can feel the water flowing toward the leak. We did, and no flow was detected.
This told me that the leak was most probably on a supply line before it came up into a baseboard heater. This was confirmed by the fact that the supply line leaving the boiler and going into the floor also was hot.
The next step was to determine exactly where all the heating lines were run underneath the concrete. This gets expensive. It requires the use of an infrared camera. You have to turn the heat up a couple hours before the arrival of the infrared cameraman. He then comes in before sunup and can see exactly where all the heating lines run by tracing the thermal trail left by the heat coming off the lines below the cement. My infrared cameraman charges a minimum of $450 to show up including the first hour, and then charges $350 per hour thereafter. All in all, however, it’s more accurate and less expensive than what I’d have to charge using my non-contact thermometer.
Once the exact location of the lines has been determined and marked with masking tape, you can then go directly over the top of the heating lines with the non-contact thermometer and find the “hottest” spot. This is usually a good indicator of where the leak is going to be.
Sometimes, things don’t work out exactly right, and your efforts are stymied by heating lines crossing underneath each other or by varying thickness of carpet and pad. The only way to confirm the leak at this point is to do destructive exploratory surgery. This means break out the jackhammer and carefully expose the heating line.
Have you ever tried to operate a jackhammer delicately?
If the area below the slab is muddy, you’re close. If it’s dry, keep sleuthing. If you’re not extremely careful, you may create your own leak with the jackhammer.
In the case of this job, we opened the floor in three different “hot” spots and found dry dirt. This caused me to resort to Tool No. 2 of my leak-detection equipment, the Metrotech audio leak detector. The problem with this leak detector is that it is so sensitive that it can hear ants passing gas. Just kidding. It is so sensitive that all electrical appliances have to be shut off inside the house. This is because the refrigerator sounds like a Greyhound Bus, and if Johnny has his stereo on in the bedroom, you will hear it.
The Metrotech has two different methods of microphone listening, and numerous scales or audio levels from which to choose. I generally start out with the floor-mount mike and see if I can hear or “see” a leak.
The Metrotech has a visual level scale, which shows the degree of noise being heard. I find this is easier to use to begin with, because if the wind is blowing outside, as it was in this case, the sounds you “hear” can be quite confusing. In any case, the floor-mount mike is placed directly over the pipe’s location and you try to find the leak.
I generally start out with 10-ft. separations between sampling points and work down to 1-ft. separations. This obviously is very labor intensive.
Again, in this case, no conclusive evidence warranted more delicate jackhammer work.
The Metrotech also has a point contact microphone, which allows you to put a probe directly onto the pipe where it comes out of the slab. Again, all electrical appliances, including the boiler must be turned off to avoid unwanted background noise. You apply the probe to the heating lines where they enter and exit the slab, “looking” for the highest degree of noise. Once you’ve determined the area of highest noise activity, you can then resort to the other two previously described methods to fine-tune the location of the leak.
In this case, the leak was right on the edge of a vanity cabinet. After more delicate jackhammer surgery, we struck pay dirt (mud) and shortly thereafter exposed the pinhole-sized leak that had caused the demise of four boilers. Amazing how much damage a little leak can do, isn’t it?
Tune in next month when we examine all the different types of leak-detection technology available to us today. Until then, Happy Dry Ditch Hydronicing!
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303/778-7772.