Cooling LEDs by heating the water saves on electricity

[Matthias] swapped out his twin-tube florescent aquarium lights for LEDs. By running tank water through the aluminum LED mounts he’s transferring excess heat into the water in the tank, in turn saving some of the electricity that would have been used to heat the tank. Couple this with roughly 35 Watts saved by moving away from fluorescent tubes and he’s got a great energy-saving hack. The LEDs used in the last aquarium light conversion were cooled by heat sinks and fans. We’d love to see this concept incorporated into that design.


  1. Chris says:

    Cool and simple idea! Do the LEDs really generate that much heat?

  2. Greg says:

    This guy must live in the arctic. Heating the tank is rarely a problem for me. The ambient temperature plus the heat created by the pumps, lights and other equipment are usually all I need to keep it at 79 degrees. If anything it overheats and I have to constantly battle with cooling it.

  3. JayDee says:

    Aluminum, water, and fish…. not good bedfellows. Aluminum leeches into the water and damages the fish gills.

  4. I’ve long thought that the lights belong at the base of the tank and behind it, with just a mirror up top to reflect the light into the tank. That way the heat from the led or bulbs will rise away from the light controller, ballasts, boards, or whatever the design uses — rather than up into them.

  5. Eliot says:

    I suppose if you consider a place like Minnesota arctic, then that well may be. When I had an aquarium, I needed a heater as well.

  6. The Clerk says:

    This would work very well with hydroponic systems

  7. Mike Nelson says:

    If the LED’s are the beefy kind (1,3,5+ watt each) then they will definitely need heat sinks, the little tiny LED’s you see in Pen lights don’t need heat-sinking, but the stronger ones do…

  8. damntech says:

    Are there guides for LED wavelength output for flora and fauna? I have been curious about the subject of light and life. Usually it comes down to I use brand x of bulb and in my tests it works better than y z. I am not questioning the tests of the plant and animal aficionado. What I wonder specifically is what amount and wavelengths of light do various common plants and animals need for better health.

  9. econut says:

    Not ‘energy saving’, it’s reducing energy.

    Saving energy would be to get rid of the aquarium and not incur the costs of the luxury. But, if it makes you feel like you’re saving the world, go for it.

  10. igor says:

    Where is the fish?

  11. vonskippy says:

    “Where are the fish?”

    Look closely at the bottom – due to being overheated in the hot water – he had to strap heatsinks on the fish as well.

  12. }{itch says:


    -shameless self promotion-
    Wrote a couple of instructables a few years ago on using LED’s to grow plants.

    I can’t find it now but in the comments someone left a graph of the absorption spectrum of plants.(Although this does change during the life-cycle of a plant)

  13. damntech says:

    Hey thanks }{itch. You also had some pretty informative comments on your work!

  14. Conglacious says:

    It would be interesting to poke some holes in the tubing for air to get through, then you could have a heater and aerator.

  15. Balbor says:


    I think it’s easy to know which LED will fit for plants growing, just compare the spectrum of aquarium fluorescents (just look in the box of it) with the spectrum showed in power LEDs’ datasheets.

    The power needed is another thing… you should look for the lumens and the spawn angle of the led.

  16. Scott says:

    So let’s see – you’ve gone from a fluorescent tube (relatively thermally inefficient) to a more illumination efficient LED system that also heats a bit of water?

    Since you’ll have to make up the rest of the heat with a resistance heater, wouldn’t it make more sense to go with a *less* efficient light source and use *all* the waste heat?

  17. googfan says:

    al isn’t good for fish.

  18. Dean in Des Moines says:

    Please don’t use salt water to cool your electronics.

  19. ratt says:

    first problem Aluminum leaking as stated
    second temperature overheating
    third -if led lights burn human eyes if looking close to it– what about the fish – are we going to blind the fish – that why the fish are at bottom to get away from the light

  20. hex4def6 says:

    I’m not convinced that he’s actually saving energy.

    Most high power LEDs are less efficient than fluorescent lights, sometimes significantly so.

  21. Greg says:

    @Eliot – Not saying I never needed a heater, just that I more often (vastly more often) needed cooling than heating.

    @anyone wondering about spectrums and plants

    This is a pretty comprehensive article.

  22. cath0de says:

    planted tanks like this don’t need heat unless it’s in your garage or cold basement. there doesn’t seem to be much room for fish in there. on the other hand, my coralife 96w has four fans on it for cooling and i still have to heat the water to keep the fish happy…

  23. jproach says:

    @scott: no, because transferring the waste heat to the water is probably not as efficient as as straight up resistance heater. Also the more power you are able to control, the better, say if you want zero heating on a warm day.

  24. Matthias says:

    Sorry fo being late, i haven t noted that this treat has grown this much
    to answer the main questions:
    1.)Pure Aluminum sure is dangerous for the fish, but in my case its eloxadized and also for outdoor use w/o getting stained. So i think it will not contact the water that much. Also the tube will get an algae layer inside due longer flooding time.
    2.)The energy “harvest” is not enough to keep the tank heated up to the desired temperature while the average temperature in my living room is at night 17degC(62F) and at day 20degC (68F) in winter times(Central Europe -Germany) It’s rather to waste not the energy loosing of the LEDs and saddle them with huge heatsinks.
    The insulating tube is detachable for warmer outside temperatures to let the heat flow in the ambient air.
    3.)Yep i have fish in there, but make a portrait of every one is not the subject here ;)
    4.)The LEDs and datasheet you ll find here: (site is in english too)
    5.) When every aquarium owner gives up his (luxury)hobby there can be switched off much carbon firing and atomic power plants. If the half reduces power by changing to efficient light there can switched off some of them.

  25. RagnarRoeck says:

    A fellow led-techer here! What is your name in the forum?

  26. Matthias says:

    sorry if i understand it wrong, but do i have to sing up somewhere in the forum? My name is Matthias

  27. Ragnar says:

    Sorry, I meant at the led-tech forum. (

  28. Matthias says:

    k, think ill sing up there. Seems to be the right forum for me ;)

  29. please help says:

    hey guys is there a HOW-TO-Do-IT guide for making this project? i would love to do this project…please help

    thanks :)

  30. Matthias says:

    HI, if you have some basic skills to work with metal, you sure can build it from the pics on flickr. Important is to use eloxated aluminum as tube. Pure Al will kill your fish!
    The beta point at this version is the connection between the square al-tube and the stainless input/output tubes. Looking forward to get my lathe ;)
    At the moment i got not much time to do a howto, but you can contact me on fb if you like. I ll sure answer any question to this theme.

  31. Nischay Mohan says:

    Hi, can you tell me how much time it takes to heat up that tank? additionally what is the capacity of the tank, and how many LED lights are there??


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


Get every new post delivered to your Inbox.

Join 96,764 other followers