Just getting out of the winter, although it keeps snowing here in Chicago. Recently moved into a new home, and have a concern regarding the main water line coming into the building.

The water line enters in the basement, at about 6 feet below the surface. Ever since we moved in, we have been fighting trying to keep the basement warm. But where the water line comes in (small little access space between outside wall and inside wall), is just super cold.

I've had a temperature sensor in there for the last 3 weeks, and even when its been 70+ outside (rare lately) the access area for the water line never went over 57.

I understand that since its below the surface, its going to take a while to warm up. Where my concern is:

1 - How is this going to work in the winter? Its keeping the basement cold now, at that depth under ground, does it get any colder?

2 - We added insulation behind the water pipe between the external wall and the pipe to seal off any drafts as best we can. It helped, we got the temperature up a bit more (54 to 57). Im cautious of putting insulation in front of the pipe between the inside wall and pipe as I feel some of the building heat needs to keep that pipe warm. Or are these main water feed pipes built for the cold?

What are the thoughts of helping keeping the basement warmer and not risking reducing the the heat (if needed) to the water pipe?

  • Assuming the following is accurate, maybe its ok to try to insulate the access area more? ** Throughout most of the U.S., the temperature of the ground below the frost line (about 3 to 5 feet below the surface) remains at a nearly constant temperature, generally in the 45 ° -50 ° F range in northern latitudes, and in the 50 ° -70 ° F range in the south. ** geoexchange.sustainablesources.com
    – cgmckeever
    Apr 30, 2019 at 22:33
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    Could you possibly edit in a picture? I'm not feeling this "inside wall/outsidewall" with respect to where the pipe runs too clearly. At 6 feet down it should be fine for not freezing, but if it then runs up behind an inner wall next to the outer wall and the outer wall is (as usual for basements) effectively uninsulated you could have freezing problems there, from exterior cold coming through the wall. If the water line comes out into the basement space (more typical in my experience) that's less of a concern.
    – Ecnerwal
    May 1, 2019 at 2:16
  • @Ecnerwal picture the wall of the room is the inside, the external wall is the outside. The pipe comes in almost at floor level, through the outside wall into a a 15' x 19' area that has an access panel on the interior wall. From there the pipe does run straight up and vanishes ,, the vertical run is against the interior wall (within the cavity I explained, not in the room itself) and is about 2 feet away from the exterior wall
    – cgmckeever
    May 1, 2019 at 12:42
  • If a single water pipe is cooling your entire basement get a Patton on it and you will be rich. HVAC lines have fins attached to the pipes and are constantly cooled by the Freon and it still takes a blower to move the cool air a ground. A cold water pipe won't be much different than a large pitcher of ice water in the room.
    – Ed Beal
    May 1, 2019 at 15:23
  • @EdBeal sorry if I was unclear .. Its not the water pipe. Its the large ass area that is cooler due to being subteranean, and where the line is coming in - and Im nervous about adding insulation to it, and then risk the temperature in that area then doesnt get the inside heat and risks freezing
    – cgmckeever
    May 1, 2019 at 18:32

1 Answer 1


This question is about thermal mass/intertia.

Suppose you are doing solar panels. The solar energy (from the panel's perspective) is exactly the same 1 hour after sunrise versus 1 hour before sunset. So why is the house so darn cold in the morning and hot in the evening?

Because it takes time for temperature to change. Heat energy has to actually move, and that takes time. And insulation is all about making it take more time.

Because it takes time, a funny thing happens underground. The deeper you are, the less the swing.

So we just talked about the daily heat cycle, which only affects the top couple inches of earth. There is also a yearly thermal cycle - which you know all about because the ground freezes. Also that awkward midwest time in the spring when the first inch of soil has thawed out, but below it is frozen - so everything turns to mud!

Anyway, if you go deep enough, the water never freezes.

How deep? In Chicago, less than 6 feet - which is why your water line is down there. Freezing destroys water mains. It never freezes, but never gets warm either.

Your basement is also down there. Same deal.

The water line is not making your basement cool. Both are cool for the same reasons.

  • ahhh ... so just being under ground is keeping it cool - and its not just the hole in the access hole in the wall. This makes sense. Sucks for me that the insulation that is supposed to be mkaing the heat exchange take more time isnt doing it quite well enough -- thank you for this feedback
    – cgmckeever
    Apr 30, 2019 at 23:19
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    Suppose you use the typical 200 gal/day that most households of 4 use. That's 1600 pounds of water. If it comes in at 50 F, and hangs around long enough to get to 70 F you have 20 BTU/pound * 1600 pounds = 32,000 BTU. Typical household furnace is 50-120 thousand BTU per hour. So your furnace had to work 20 minutes to warm up the incoming water. In practice a lot of that water ends up being heated by the hot water heater. May 1, 2019 at 4:13
  • @SherwoodBotsford Appreciate the Thermal Dynamics, but not sure how that relates to understanding how to keep the cold from entering through the cavity without risking not keeping that area warm enough for the pipe to not freeze
    – cgmckeever
    May 1, 2019 at 18:34
  • I was address the cause in your title, showing that it is NOT the cold water that is cooling off the room. You can't solve the problem if you are looking at the wrong palce for the soluiton. Now I will go edit it and see if I can address your 'real' problem. May 2, 2019 at 21:35
  • Except that's wrong. You don't get efficient thermal transfer because pipes are not heat exchangers and the flow isn't consistent. When the water is flowing, it moves through the pipe far too quickly to draw much heat from the basement. When it is quiescent, then yes, 100% thermal equalization, but there's not much inventory of water in the pipe. May 2, 2019 at 21:44

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