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Thread: Cold nights= evaporation??

  1. Back To Top    #1

    Join Date
    May 2015
    New Milford, New Jersey

    Cold nights= evaporation??

    Hi everyone,

    Is it common to have more evaporation when we are having cool nights and warm days?? Trying to determine if it's a leak, thanks for your help!

    17x34 and ranges in depth from 3 ft to 6 ft.; I think 20-22 thousand Gallons
    IG -Vinyl with Waterfall
    Hayward Super Pump 1.5 HP
    Pentair DE 60 Filter
    Hayward H300 Heater; Taylor K-2006 Complete

  2. Back To Top    #2

    Join Date
    Jul 2014
    Hope Mills, NC

    Re: Cold nights= evaporation??

    Cool temps generally equate to lower humidity which will cause more evaporation...but it is such a small difference.
    16 x 32 17500 gallons
    Vinyl in-ground
    Hayward 250# Sand Filter
    1 HP Pump
    Hayward SWG

  3. Back To Top    #3

    Join Date
    Oct 2013

    Re: Cold nights= evaporation??

    Cold nights when you have warm days usually means very low humidity. Around here in July/Aug the dew point climbs into the 70s and the temp will not drop much at all overnight. In those conditions three things happen: 1) Air temp is close to pool temp. 2) Very little wind. 3) Extremely high humidity.
    All three of those lead to almost no evaporation.
    Once the dew point drops in the fall, we get more breeze at night, much lower humidity, and much cooler nights. Assuming your pool is heated (still the same temp) each of those three things lead to much higher evaporation.
    I notice it when it rains with our autocover, the cover pump leaves 1/2 inch puddles in places, in July/Aug those are still there days later if I haven't done anything with the pool, in the fall they are gone by morning (along with most of the pool's heat).
    20,000gal in-ground 16x36 sentry pools vinyl liner, Pentair sand filter, Pentair minimax NT heater, auto-cover, Polaris 280 cleaner.

  4. Back To Top    #4
    Mod Squad
    Join Date
    Aug 2012
    DFW, TX

    Re: Cold nights= evaporation??

    1/8"-1/4" evaporation per day is typical. The best way to check for a leak is a bucket test. More here, Pool School - Leak Detection
    TFP Moderator
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    2012 build and pics, 20k gal gunite, black onyx pebblesheen, OK flagstone, IntellifoVS, cart filter w/Pleatco, IC40 SWG, Solartouch, 5 12'x4' solar panels, HP50HA heat pump, 8mil solar cover, borates, TF-100 test kit, SONOS, Doheny's Discovery Robot, hot tub on bleach

  5. Back To Top    #5
    JoyfulNoise's Avatar
    Join Date
    May 2015
    Tucson, AZ

    Re: Cold nights= evaporation??

    The evaporation rate of water in your pool is determined by the temperature differential of the water and the air as well as the relative humidity and wind speed. I find that, as the weather cools and the air temps get lower at night, my pool water is warmer than the surrounding air. I live in the desert so RH is always low. Like clockwork, I can hear the autofill start running at night after the sun goes down.

    See this link for a good primer on water evaporation - Evaporation from Water Surfaces
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

  6. Back To Top    #6
    borjis's Avatar
    Join Date
    Aug 2014
    Pacific NW

    Re: Cold nights= evaporation??

    Funny the other day when I took off the bubble cover at 7am (45 degrees outside / pool water was 82) it looked like I lifted
    the lid off of a boiling tea kettle, very visible evaporation. Put the cover back on to conserve heat / water.
    16x32 IG Vinyl, 13,000 Gals. Hayward S-244T sand filter, SP2810X15 pump
    (1.5 HP motor) Jandy Lite2 LJ250N gas heater. TF-100 Test Kit.

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