**What I was trying to find on this forum was anything about going from geothermal directly to a heat exchanger in the ductwork**

Hi guys,
I'll start but saying that I am renting a 1950's home with an old furnace and ducting, but no air conditioning. The summer heat combined with the severe lack of proper insulation has me searching for a cheap way of cooling it.

Now this concept has to be non-destructive and removable. I am drawing the technical aspects of this from the passive water cooling system I built for my computer using a 100Liter tank to cool a 200watt cpu to ambient under load.

The house
-Uninsulated unfinished, concrete basement
-Single Story house of roughly 8000cu.ft.
-exterior temperature between 20c and 33c
-4pm exterior air vs. interior air temperature difference (all windows,shades and doors closed all day)
-- at 32c outside - 28c inside and basement was steady 16c
-Basement air temperature is a constant 15c +/- 2c

So here's my idea.
-Large resivoir(s), preferrably steel, possibly multiple smaller ones for easier install
--Placed on the coldest tested part of the basement floor
-Adjustable flow circulation pump to adjust for best performance
-Some kinda of heater core/radiator to install in the ductwork
-Add a switch upstairs to turn on furance blower (which should be done anyways)

Just an idea, but if you guys think it wouldn't be a waste of money "$/degree" wise, I'll give it a shot..

Basement air temperature is a constant 15c +/- 2c

The issue is that your basement (and the ground) will not be a constant temperature once you start adding more btus.

Well water would be a different story - it will maintain a constant temperature and in that case, the primary issue is humidity control (a solvable issue in a tight house).

Won't work:

1) Basement will lose its cool
2) duct and blower heat gain
3) piss poor dehumidification

A water coil with well water would bring some relief.

I infer from the use of *C temps that OP is Canadian, suggesting groundwater in the 4-8*C range. That could provide both useful cooling and dehu if run through a water coil with a properly selected and configured blower.