I have kind of a crazy idea I have been scheming - I live in Alaska, and have a private well - the groundwater here is very cold(40-45F) or so. The last couple of summers have been miserable hot up here(A/C is very rare), and I have been looking at cheapy single room or diy air conditioners, and ran across a simple fan with a coiled copper pipe circulating cold water. That got me to thinking, why can't I scale that up, and have a cold water circulating pipe inside my furnace vent. I found some pretty inexpensive Water to air heat exchangers online, with copper pipes, and aluminum fins.

When it gets really hot inside, I turn the furnace fan only on, just to circulate some air. So I figured I could just turn the fan on, and run my sprinklers a bit outside, or do dishes to circulate cold water through the heat exchanger. I wouldn't be looking to cool the air dramatically, just slightly - enough to give some relief on very hot days. Here is a diagram that kind of explains what I am thinking. I also added a loop for the hot water heater, thinking I could switch the heat exchanger over to hot water in the winters.

Heat exhanger scheme

How crazy is this, and what would the major problems be? I do have a condensate pump already, and I figure the heat exchanger will sweat so I would add a drain there.. Would I be adding so much moisture to the supply air I would also need a de-humidifier? Would the supply air not really cool down at all like I am hoping?

Thank you for any response.

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    dandelionenergy.com/blog/geothermal-cooling Same idea, but use a closed loop system - otherwise you are either raising humidity (not good in the summer) or wasting water or both. May 4, 2020 at 19:06
  • Yeah, the humidity would be my main concern. I figured I could run a 50 pint dehumidifier in the house as well though. This is a ghetto diy system I'm hoping to build for $200-$250. So drilling geothermal lines is a little out of my price range. As far as wasting water.. This would be using water I am using anywhere in the house.. I wouldn't be just draining the water, and I wouldn't be putting constant strain on my well pump.
    – Ben
    May 4, 2020 at 20:00
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    A dehumidifier adds more heat. The problem with an open-loop system is that your water usage will probably be nowhere near the amount of cooling you want. But I do see your point - open loop == existing plumbing, closed loop == Add 2x the existing plumbing, plus a pump. May 4, 2020 at 20:03
  • In thinking about humidity... My air intake is inside my house.. So if warm moist air is passing over the cold heat exchanger, condensing into droplets, draining out the bottom, and being removed by my condensate pump.. Am I not lowering the indoor humiditiy in effect? Im sure i'm way over simplifying that, or completely wrong..
    – Ben
    May 4, 2020 at 20:08
  • If it is cold enough, yes. But I'm dubious that a simple setup like you suggest (simple in the sense of "cold water flowing through, not a refrigerant cycle") will get much water to condense out and at the same time you will inevitably end up deciding to run more water through the system in order to increase flow which means more evaporation into the house. May 4, 2020 at 20:14

2 Answers 2


Using only cold water to lower a buildings temperature was common many years ago. I have not seen any of the systems that still work but I do know or was told that they worked. This would be similar to a typical A/C system except that the cooling medium would be water instead of a refrigerant cooling the air. Know this that most large buildings, schools, hospitals, and office buildings use cooled water to do the A/C since it is easier to circulate a cooled water than to have spot cooling everywhere. In your case, instead of using a refrigerant to cool the water, you will use a dedicated cold water source as your cooling medium. A cold water source is located, a well, an underground stream, or an aquifer that is tapped into and the cold water was pumped into a water coil similar to an A/C coil and the discharge water, now slightly heated is returned back into the source. This idea will work if the source water is cold enough, you can remove and return enough water to suit your needs, and it is allowed by the codes concerning this action. Will your idea work, yes, is it allowed, ?, is it cost effective, I do not know.

  • With ground water that cool it probably would work, geothermal heating and cooling has been and is a thing some systems pull water from 1 well and dump it back in another on the other side of the house, the cost of a capped well is the negative here I have seen people use the discharge for watering fields.
    – Ed Beal
    May 5, 2020 at 15:00
  • Yeah, my idea is more like energy recovery of the cold groundwater i am already using. I do run sprinklers in the summer, and we use a lot of water in general with laundry, dishes, showers, gardening,etc. The way i will connect it will force cold water through the exchanger before it goes to the water heater so will make use of hot water used as well. As far as whether it is code, i highly doubt that. I will install it in a safe manner and It will be easy enough to take out though. Will go along will with the rest of my non code house.
    – Ben
    May 5, 2020 at 17:03
  • If you are still looking for more information on using underground water to cool your home do a search on the underground river or the 4th river in Pittsburgh, Pa.
    – d.george
    May 9, 2020 at 9:47

I am considering the same system but going to rout my cold well water through a 150 gallon tank but use a 3/4 copper coil inside that tank to exchange the coolness to the tank water.

Why? To bank cold water every time there is any water used in the house and the well pump comes on, 48 degree water flows though the copper pipe and if the water in the tank is above 48 degrees there will be an exchange of heat from the tank to the cooper coil in effect heating my well water as it goes though thus cooling the tank water.

Then I will pump the cool tank water through a radiator inline with my HVAC. What do you call that? I don't know how much lower the water will need to be then the 73 degrees my air conditioner is set at but I have no doubt I can achieve some cooling effect.

Will it be enough to completely cool my house and turn off the hvac cooling system and only run the fan? I think so as long as there is cold enough water in the tank. Or, I could use the extra cooling to augment my HVAC resulting in cooler air at the vents and thus the system would run less to achieve the same cooling of the house?

I will be able to run it ether way to see. I can also make the tank larger such as 300 or 500 gallons to bank more cold water. All the tank has to do is hold the water, not hold well water pressure as the well water passing through is contained in the coil. It just passes though and absorbs heat leaving coolness in the tank.

I have a nice plastic IVC 300 gallon tank I got for 25 bucks. No way to get that into the basement but I could bury it behind the house and run well water into and out of it and insulate around it, cheap but good-enough.

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