We've discussed this before.. And it's still puzzling me.
I even injected foam under the boiler to cut down the transfer.
However, I now have some new sump holes installed. (with pumps).
And luckily (or not) there is cold ground water coming into the sumps.
Had some rain this month.
Anyways, when I checked the incoming water, it was at 61 deg F.
And I'm pretty sure it's not going to get much colder than 60F.
My theory is, this water is flowing downhill to my house from the north.
It has to flow under the street. I believe it might be picking up some heat
from the sewer main pipes (and perhaps a little from the water main pipes).
The sewer main is about 30 feet (and about 16 feet down) from my foundation.
The water in sewer mains is being used in Europe as a heat source for heating.
So, the same effect might be heating my basement..
Now that I think about it, if the water is flowing downhill, just a few feet under the pavement,
there is the possibility of some slight solar heating of soil under the roadway and the water it's carrying.