I know that normally, swamp coolers take in external hot dry air, and put it out as cool wet air.

I live in the hot So. Cal. desert area. A small swamp cooler is cheap to buy, but won't do my whole house.

My thought: Can I take the hot, dry, internal air, get it moist/cool, send it through the central air ducts (to put some cool air into the rooms), and then just cycle that around again? The thinking is that it will eventually put enough water into the air that the humidity will persist long enough to actually be cool, without having to constantly re-cool fresh hot air.

But ... this seems too simple -- if it would work, wouldn't this have been done already?

  • Swamp coolers are single pass. You cannot recirculate like an a/c or heat pump or a furnace. Commented Jul 27, 2017 at 17:08

1 Answer 1


Where they work, swamp coolers work because evaporating water cools the air being pulled in (via latent heat of vaporization - go visit a chemistry site if that's a concept you haven't gotten in your education.)

Making the air humid does not, in itself make it cool - at a given temperature, humid air feels warmer to people, as sweat evaporates poorly. Starting from hot dry air, the swamp cooler makes cool, moist air. Starting from warm moist air, it just blows warm moist air around.

So, if you recirculate swamp-cooler air, the air in your house becomes increasingly humid, with two effects - one is that it evaporates less water at the swamp cooler, and thus is cooled less, and the other is that the internal air becomes more humid. In the long term, it will be more uncomfortable in the house than out, as house temperature will rise to outside temperature, but be more humid.

  • This is not entirely true. Evaporation does cool the air as the water absorbs heat from around it. I’ve seen someone use a central swamp cooler in a rather humid place to cool their house, and it worked quite well. The way it worked is a fan blew external air (which was at a constant humidity) through a pile of hollow bricks, and the bricks would get sprayed with water every once in a while. The trick is to pull the air from outside rather than recirculate the air inside. That way you get a constant stream of cool air in your home. Commented Apr 4, 2023 at 1:07
  • @Jean-LucNacifCoelho Please read the question which is specifically about recirculating air through a swamp cooler rather than drawing air from outside!
    – Ecnerwal
    Commented Apr 4, 2023 at 1:19
  • Yes, but up until the point where the air saturates with moisture, it does become cooler as the water absorbs heat. Commented Jun 11, 2023 at 6:47

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