I will keep this short and clear as I can.

My home has a creek that runs through it about 20' from the side of the house. It is shaded and quite cool even in the summer heat. If I got say an automotive AC evaporator and plumbed lines to and from the creek, and just cycled cold water through the system and stuck a fan in front of it...

I understand of course that would be much less efficient than actual refrigerant, but colder is colder. It would work wouldn't it? The fins would cool down, and air flowing over it should exchange heat into the water headed outside.

  • 1
    It would work, but the question is whether it would work enough to make a difference while not costing more than the equivalent amount of energy pulled through a window unit. If the air/water temperature differential isn't at least 20 degrees in the room you'd hardly notice it. You may gain heat in the plumbing.
    – isherwood
    May 11, 2020 at 21:38
  • You say "stream powered". Does that include the pumping?
    – isherwood
    May 11, 2020 at 21:41
  • you may require a permit from the local fish and wildlife government department
    – jsotola
    May 12, 2020 at 4:30

2 Answers 2


I know that seems like a cheap easy hack. However it's not going to work very well, and to get it to work at all you'll have to pour some fairly serious capital into it.

Given that, you would be better off using real heat pumping with freon. But yes, use that creek water: it is an excellent heat-sink and will greatly increase the efficiency of the unit. Heat pumps work best when they are pumping heat "downhill", i.e. the ultimate heat sink is colder than the space they are cooling.

There are several sources for water-sourced heat pump equipment, but the most obvious is a marine air conditioner/heat pump. They use seawater as their ultimate heat sink. Seawater is very corrosive; your creek water can't be nearly as bad.

Going with a proper heat pump instead of merely an air conditioner means you can set it for reverse mode, and get heat out of it also. However that will stop working when ambient temp gets too cold.

  • I like it, and this is why I come here. I knew there would be a way to use cold water in a more or less direct way. A new one of those is way out of my budget, but it gives me something to research. Thanks guys.
    – Toaster
    May 11, 2020 at 21:52

I wrote a piece on May 5th for a similar question asked by @Ben that he posted on May 4th. His post was "Groundwater cooled heat exchange- forced air". My answer may add some ideas. Also, in 1965, Whirlpool corp introduced the first residential natural gas fired A/C system utilizing Ammonia/water (NH3/H2O), where chilled water was circulated to the house to do the cooling. Other companies that followed suit were Bryant and Arkla (now Dometic). The chilled water coils were very large, larger than the refrigerant coils of today. Searching these systems may give you some ideas that you can use.

This was my answer to his question. Using only cold water from a creek or large water source 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.

One more thing, years ago, some of the buildings in Pittsburgh, Pa. utilized cold water pumped up from the "4th river" under Pittsburgh. I thought it was a river but have now learned that it is actually an aquifer or large pool of water. my 2 cents

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