# Warm spot under the house floor **URL:** \ **Category:** Factual Questions\ **Created:** [October 13, 2009, 6:24am UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634 "2009-10-13T06:24:18Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![MaxTheVool](https://avatars.discourse-cdn.com/v4/letter/m/9fc29f/32.png) [@MaxTheVool](https://boards.straightdope.com/u/MaxTheVool)\ **Post date:** [October 13, 2009, 6:24am UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/1 "2009-10-13T06:24:18Z")
A few days ago, my wife noticed that there’s a big warm spot under the tile floor of our entry hallway and kitchen. Also, our cold water tap sometimes runs warm, presumably because the pipes go through this warm spot, so the water is heated up (if you let them run, it cools back down, presumably because it was only the water that stayed there for a while that heated up). How concerned should we be about this? Does this ring any bells with anyone? thanks ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [October 13, 2009, 7:15am UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/2 "2009-10-13T07:15:12Z")
The hot water pipe itself? Duct work directly under that spot? A light fixture in the basement? An electrical problem? Animals living under the floor? Radon gas?\* Ghosts?! \*kidding. ---
**Author:** ![FloatyGimpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/floatygimpy/32/7750_2.png) [@FloatyGimpy](https://boards.straightdope.com/u/FloatyGimpy)\ **Post date:** [October 13, 2009, 8:21am UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/3 "2009-10-13T08:21:46Z")
That happened at my grandma’s house and it ended up being a burst pipe shooting hot water on the the floor. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [October 13, 2009, 10:59am UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/4 "2009-10-13T10:59:54Z")
We have warm lines on the floor, above the ductwork that runs to the heating vents. Also, when we had our basement finished, a duct was run between the same pair of joists that had a large water line, o we get warm water from our cold faucet in winter (for a short time). Can you go down a floor and look up? If not, you could try to correlate the heating vents to the warm spot. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [October 13, 2009, 12:44pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/5 "2009-10-13T12:44:48Z")
What kind of heat do you have? And do you notice the warm spot only when the heat is on? We’ve got warm spots from the steam heat pipes running under the floor. In my fantasy world, one day I’ll re-route the pipes so they run under the floor between the bathroom and the bed where the warm spot would be useful. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 13, 2009, 12:55pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/6 "2009-10-13T12:55:23Z")
You’re not near Yellowstone are you? I’d sure hate to find a supervolcano breaking through \*my \*entryway floor. ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [October 13, 2009, 1:04pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/7 "2009-10-13T13:04:59Z")
Make sure it’s not a furnace fire. When I was a toddler, I found a hot spot on my bedroom floor and tiny wisps of smoke coming through a knothole and woke my parents to tell them. It turned out to be a fire out of control in the furnace in the basement (I’m not clear on whether the basement itself had caught fire or the walls of the furnace unit or what; I was pretty young at the time). Everyone but me was asleep and the fire was underneath the kids’ bedroom. ---
**Author:** ![Zsofia](https://avatars.discourse-cdn.com/v4/letter/z/7bcc69/32.png) [@Zsofia](https://boards.straightdope.com/u/Zsofia)\ **Post date:** [October 13, 2009, 1:09pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/8 "2009-10-13T13:09:29Z")
That’s not where the dog likes to sleep, is it? Sometimes it’s the simplest explanation. 🙂 ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [October 13, 2009, 1:28pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/9 "2009-10-13T13:28:10Z")
a long shot. floor tiles can hold a lot of heat, does that spot get major sunlight during the day. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [October 13, 2009, 2:24pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/10 "2009-10-13T14:24:04Z")
I have the same thing in my living room. - There are no water pipes near the spot. - There is a forced air duct that runs near the spot but the warmness is confined to about a 3 foot diameter spot, not the length of a duct, and it’s warm even when the AC is running. - There is a light fixture near the spot (for the room below) but the spot is warm even when the light hasn’t been on. - We don’t have a dog. Probably some kind of radioactive decay. ---
**Author:** ![Tastes\_of\_Chocolate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tastes_of_chocolate/32/3232_2.png) [@Tastes\_of\_Chocolate](https://boards.straightdope.com/u/Tastes_of_Chocolate)\ **Post date:** [October 13, 2009, 2:34pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/11 "2009-10-13T14:34:30Z")
> [@Quercus](#): > > We’ve got warm spots from the steam heat pipes running under the floor. In my fantasy world, one day I’ll re-route the pipes so they run under the floor between the bathroom and the bed where the warm spot would be useful. The house I grew up in had a seperate tub and shower in the bathroom. The hot water pipe ran under the tub to get to the shower. It wasn’t uncommon to walk by the bathroom in the morning and see someone standing in the empty bathtub, brushing their teeth. ---
**Author:** ![cjepson](https://avatars.discourse-cdn.com/v4/letter/c/a9adbd/32.png) [@cjepson](https://boards.straightdope.com/u/cjepson)\ **Post date:** [October 13, 2009, 3:58pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/12 "2009-10-13T15:58:13Z")
We had the exact same problem that you describe. It was a water leak in our heating system. (Our house is on a concrete slab, and we had baseboard heating; the baseboards were fed by pipes that ran under the slab. Of course, the warm spot appeared only during heating season.) If your problem is a leaky pipe, the difficulty of fixing it will depend on the type of pipe. IIRC, copper pipe can be fixed pretty easily, but if it’s galvanized pipe, the entire section of pipe has to be replaced. We ultimately decided just to get a new heating system so that we wouldn’t have to worry about future leaks. (We had been thinking about doing that anyway, and fortunately were in a position to do so.) Our water bill is now a LOT lower. ---
**Author:** ![MaxTheVool](https://avatars.discourse-cdn.com/v4/letter/m/9fc29f/32.png) [@MaxTheVool](https://boards.straightdope.com/u/MaxTheVool)\ **Post date:** [October 13, 2009, 4:23pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/13 "2009-10-13T16:23:16Z")
It’s in the ground floor, and there’s no basement. And we have no central heating at all (being in California). The only thing in the house that heats things, as far as I know, is the hot water heater. It seems not to be leaking, nor does it seem (based on the naive listening approach) to be running at all. It’s certainly not just where the dogs are lying, that wouldn’t turn cold water hot. My theory is that maybe the neighbor’s hot water heater is leaking? (It’s a townhouse, so right up against houses on both sides). ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [October 13, 2009, 4:27pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/14 "2009-10-13T16:27:22Z")
Just to be sure… you do NOT have radiant heating in the slab? The kind with hot-water pipes that circulate water through the slab comes to mind. ---
**Author:** ![pojimba](https://avatars.discourse-cdn.com/v4/letter/p/bcef8e/32.png) [@pojimba](https://boards.straightdope.com/u/pojimba)\ **Post date:** [October 13, 2009, 7:32pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/15 "2009-10-13T19:32:16Z")
I was gonna say your clothes dryer wasn’t vented properly; been there and done that. ---
**Author:** ![MaxTheVool](https://avatars.discourse-cdn.com/v4/letter/m/9fc29f/32.png) [@MaxTheVool](https://boards.straightdope.com/u/MaxTheVool)\ **Post date:** [October 13, 2009, 9:26pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/16 "2009-10-13T21:26:57Z")
> [@Sunspace](#): > > Just to be sure… you do NOT have radiant heating in the slab? The kind with hot-water pipes that circulate water through the slab comes to mind. Unless I’ve had it for 4 years without being aware of it and it just now has suddenly gotten turned on. Stranger things have happened, but it seems unlikely. > [@pojimba](#): > > I was gonna say your clothes dryer wasn’t vented properly; been there and done that. Presumably that would only happen while the dryer was running? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 13, 2009, 9:32pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/17 "2009-10-13T21:32:37Z")
> [@](#): > > That’s not where the dog likes to sleep, is it? Sometimes it’s the simplest explanation. Mind your cause and effect… All the animals I’ve lived with in my mom’s house loved sleeping on the spot directly above the furnace, since that was the warmest spot on the floor. Unfortunately, that spot was also right directly in the doorway between the kitchen and the dining room, the most traveled route in the house, so you always had to watch your step. ---
**Author:** ![Arnold\_Winkelried](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@Arnold\_Winkelried](https://boards.straightdope.com/u/Arnold_Winkelried)\ **Post date:** [October 13, 2009, 10:00pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/18 "2009-10-13T22:00:25Z")
Do you sometimes hear a sound coming from that area? A low, dull, quick, sound - much such a sound as a watch makes when enveloped in cotton? If so there might be a BEATING HEART under your floor! (apologies to E.A.P.) ---
**Author:** ![hermann](https://avatars.discourse-cdn.com/v4/letter/h/b487fb/32.png) [@hermann](https://boards.straightdope.com/u/hermann)\ **Post date:** [October 13, 2009, 10:08pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/19 "2009-10-13T22:08:57Z")
If you are on your own water meter, look at it to see if the “tattletale” is moving. Of course, you should make sure nobody uses the water while you’re doing this. ---
**Author:** ![sideshowkar](https://avatars.discourse-cdn.com/v4/letter/s/5e9695/32.png) [@sideshowkar](https://boards.straightdope.com/u/sideshowkar)\ **Post date:** [October 13, 2009, 11:27pm UTC](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634/20 "2009-10-13T23:27:19Z")
I had something similar a few years ago. It turned out to be a slab leak - just a minuscule little hole in one of the pipes under my concrete slab. I probably had it for a few months, but there was hardly any water leaking out, so I didn’t notice it. I did smell something like mildew every time I came home from work though, but I couldn’t figure out what it was. Then one of my cats started sleeping right over the spot, which was odd for her - she prefers the bed to the floor. I thought it was because it was the wall next to the water heater, but then I realized she wasn’t right up against the wall, so I felt the floor and noticed it was warm. Then I realized my hand was a little damp. This one little thing made my life a nightmare for about 3 months. Even though the leak was really small, almost all of the carpet in my 1000 sq ft house turned out to be wet. The padding underneath is like a sponge. I ended up getting rid of all of it and had my concrete slab polished… which turned out to be really good when the water heater sprung a leak… And because I just have the slab as my floor, I can totally feel a bunch of warm spots now, but I know they’re just hot water pipes. When I was getting it taken care of, the plummer told me that a good way to test for a leak is to put something plastic over the spot and leave it for a few days. If there’s a leak, water will condense underneath it. This was something I’d already noticed - I had a bunch of plastic bins under my bed and those were the spots that were soaked when everywhere else was just a bit damp. I don’t know how it will work with tile, though, but good luck. [Next page](https://boards.straightdope.com/t/warm-spot-under-the-house-floor/513634.md?page=2)