Strange Heat Radiation Problem

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We've been in the house for 9 years. It is a townhouse, and is about 20-25 years old. Last night, I noticed a good deal of heat radiating from a small area of the on-grade concrete slab. As far as I know, I do not have radiant heat (but I suppose anything is possible, especially considering the way things were done in these houses). The area is about 8-10 feet square, and extends from a tiny powder room to the adjacent laundry room. The powder room has tile on the concrete, the laundry room is bare concrete. Overall, the slab is roughly 15 x 50.
The hottest spot seems to be in the area close to where the powder room sink drain goes into the floor. The drain pipe itself is not hot, just ever so slightly warm from conducting the heat up from the floor. It's barely noticeable, actually. The floor, however, is VERY warm to the touch- I would estimate somewhere between 110-120 degrees. I felt the heat even through a bathroom rug (and the tile)! I put a thermometer on the floor at what felt to be the warmest spot, and the air temperature at the floor was about 15 degrees higher than the rest of the house (86 vs 71).
The further you get from this area, the less warm the floor. I do not see any pipes (other than the drain) going to the floor. There is a drain in the laundry room for the washing machine. I do not know what path the drain takes once it is under the slab. The main drain stack is on the opposite wall. The main stack pipe did not feel warm.
I thought I heard the sound of water running in a pipe. This sound was coming from the wall nearest to the warm spot (wall is shared with my next-door neighbor). I shut off everything in the house that made noise, and put my ear to the wall. The sound was defintely there, sort of a hiss. I next looked at my water meter, and saw that the tiny white spinner on top was turning. There was no water running in the house that I know of.
I checked with the neighbor, and there is nothing odd going on there.
We have heat pump heat, and the coil is located on the wall opposite from the hot spot. No smoke or odd smells.
I am stumped, but I have one possible theory, which is that I must have a small section of radiant heat under the powder room that I have no control over. This wouldn't totally surprise me, as for example, I have no control over my porch light. The porch light is on a light sensor, and there is no switch- just the breaker. So, anything is possible in this place. They did some really odd things.
Any ideas of what is going on here? Thanks.
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Sounds like a hot water leak (probably in or under the slab), from the plumbing that supplies the powder and/or laundry rooms. Close the cutoff valve on your water heater and see if the noise stops.
- Dennis Brothers
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Shut off all your faucets and observe your water meter for about 15 minutes. If it moved you have a leak under the slab. Get a plumber get a listening device on the slab to locate the leak. Ron

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there's a leak in the pipes that run under your slab. a pipe that runs from your water heater to elsewhere has a hole in it. turn off the hot tap valve on the top of the water heater and see if the hissing and heat goes away.
the fix is to cut a hole in the floor, dig down to the pipe, and fix the leak.
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Thanks Charles, Speedy Jim, and Dennis- As far as I know, there are no pipes in the slab. The pipes appear to run through the walls. The hot water tank is in the laundry room There is no drywall there, so I can see the pipes along the ceiling go down to the washer, and branch off to the laundry room, again high up along the ceiling. It most likely then turns down the wall in the powder room to the powder room sink. I suppose there could be a leak there (behind the wall), but absolutely nothing is wet, or even damp. I guess I can cut a hole in the drywall behind the powderoom sink to see if the pipes continue down into the slab from there, but I can't imagine that they would have run the pipes in the slab, when it is easier to run them between the joists. These are the only plumbing fixtures on that floor. Maybe it's wishful thinking, but generally, they did whatever was easiest (which is why there's no switch on that porch light, I think)
Does any of that change your thoughts at all? Thanks again..
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On 4 Nov 2005 09:53:58 -0800, snipped-for-privacy@verizon.net wrote:

In a COA, the porch lights may be required to be on full time. If that was in the charter for the COA, then the COA saved some money, and provided a means of enforcing the rules, by not installing a switch on that light.
The COA I lived in for a while had done exactly that. The also assumed responsibility for maintaining those fixtures, including lamp replacements. They ended up replacing all of the incandescent porch fixtures with fixtures suitable for use with compact flourescent lamps, and fitted with daylight sensors to turn the lights off during daylight hours.
--
Art Greenberg
artg AT eclipse (remove this) DOT net
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that could be. This is an HOA, and we are required to keep the lights on, but we are responsible for all maintenance on them.
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snipped-for-privacy@verizon.net wrote:

Sounds like leak in hot water line IN the slab:-(
Shut off Main supply valve and see if "hiss" stops.
Don't rush to have slab dug up. See if there are other ways to route the line above the slab.
Jim
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Now that scares me. The thought of a hot water pipe leaking under g round! If everything is turned off and the meter is running, the water is going somplace. Check the pipes from the water heater and see if they are hot as in the water moving through.

Possible, but I think you'd have notice in the past nine years.
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wrote:

Clearly you have a hellmouth forming in your basement. You should either paint a pentagram on the floor around the spot, or dig it open, depending on which side you're on.
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The thought had occurred to me:) Or perhaps a geothermal opening of some kind.
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Thanks. You'll see in another post that I am pretty sure there are no pipes in the slab, as I can see them overhead in some places. Also, as it turns out, my wife says that she _thinks_ she has noticed the warmth in the past (she spends more time down there than I do).
Anyway, assume for a second that my theory is correct. How would such a system operate? BTW, we are 100% electric, if that matters. Thanks again!
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You still have the running water issue. Closing the water heater cutoff valve is a simple way to gather more information (unless you're one of those folks who believe "a few days in the library can often save hours in the lab" :). If in fact you're losing hot water, and something in your house is suddenly getting warm, I'd not be inclined to think it was mere coincidence.
- Dennis Brothers
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I'll give it a try when I get home. I don't really know if I am losing hot water. I don't hear water running in, out, or anywhere near pipes I can touch (which is from where the cold water comes in, to and from the water heater, and up to a point before the powder room). I only hear the slight hiss behind the wall. It could be noise from next door, too. That only leave the mysterious spinning disc on the water meter. BTW, there are two meter readouts- one on the meter, and another, connected by wire, to an odomoeter-type meter outside. Could the spinning thing just be an indicator that the feed to the outside meter is working?
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There's nothing "mysterious" about it -- it means you have a leak. Several people have told you this already.Why do you find it so hard to believe?

No. It's an indicator that you have a leak.
How hard is it to close the shutoff valve at the water heater? Seeing whether the noise stops, and the water meter stops spinning, would certainly provide a lot more information about what's going on. Why haven't you done this yet? Afraid of what you'll find?
--
Regards,
Doug Miller (alphageek at milmac dot com)
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provide a lot more information about what's going on. Why haven't you done this yet?
Not home right now. Will be doing it when I get there.

You bet.
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--
Regards,
Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

Then what might be causing it? Is he on the tip of the volcano that is about to erupt?
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snipped-for-privacy@verizon.net wrote: <SNIP>
Could the spinning thing

No. Spinning means water being used.
Jim
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likes a hot water line leak in / under the slab to moi.
If you shut off the valve to your water heater, does the hissing noise stop, and the slab gradually cool down?
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