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Thread: HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

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    Join Date
    Jun 2016
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    HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

    We have a brand new in-ground pool and hot-tub. Big pool- 50x20, big spa, 10x9. We have a big heater too- 400 btu propane heater. However, even when the starting temp of the spa is 81 or so, it's taking over 1.5 hours to get up to 99-100 degrees! I think that's WAY too long. We worked with a "pool consultant" who was incredibly flaky and incompetent so I have a feeling he probably has never installed a spa this large. I'm wondering what kind of heater is used at resorts or public pools/spas? Do they use two heaters? I'd rather have gotten a more expensive/bigger heater that would heat it quicker (30 mins???) so we didn't have to wait HOURS (and I'm worried about winter now!) to enjoy our hot tub.

    Any ideas or suggestions would be greatly appreciated. Or is it too late at this point to change/add equipment?

    Thank you in advance for any help!!
    Brand New (June 2016) IG 42,000+ gallon pool+spa. Pool 50x20', Spa 10x9, plaster, Pentair System 3 Sta-Rite filter, Sta-Rite Max-E-Therm 400 heater, 2 Pentair Intelliflo VS pumps, 1 booster pump, Pentair Easy Touch Control System, Well water.

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    Mod Squad jblizzle's Avatar
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    Re: HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

    What is the volume of water in your spa?

    VOL * 8.345pounds/gallon * 20degrees = BTU required / 320000 BTU/hr(assumed 80% efficiency) = hours to add 20 degrees not accounting for environmental losses

    For example, if you have 2000 gallons using the above would estimate about 1 hour to add 20 degrees not accounting for environmental losses.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
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    Mod Squad jblizzle's Avatar
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    Re: HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

    Note, I had a 400k BTU heater at my previous house on my ~700 gallon spa.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

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    Jun 2016
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    Martinez, CA
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    Re: HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

    We have a very large spa and 400k heater. As you stated, it takes considerable time to get to temp. What has helped me is the iaqualink controller so I could turn on the spa remotely ahead of use on my phone.

    as to adding an additional heater, you may have to replace the existing gas piping or used a divorced pressure regulator in order to provide enough gas to the burners.
    18,000 gunite pool/spa combo. Pebble tec, iaqualink rs8, cl580 filter, aquapure 1400, 400k btu lx heater, 10 solar panels, jandy 1hp, 1 1/2hp, and 2hp stealth pumps for circ, spa, waterfall

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    txnole's Avatar
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    Aug 2014
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    Amelia Island, FL
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    Re: HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

    Based upon your expectations (faster heating), your heater is undersized. Our 400k heater is paired to our 550g spa
    COMPLETED BUILD THREAD - 15'x29' rectangular offset shotcrete pool; 14,100 gal; 5'x7' raised spa with 400k btu fire feature; 7' spillover; 25' leuder stone raised bond wall w/waterfall; Pentair SWG; Pentair VS (pool); Pentair 3/4hp feature pump; 1hp spa blower; Pentair Cartridge filter; Pentair “Easy Touch 8” wireless; Dolphin Oasis Z5 robot; Solar Hydronics iSwim solar panels; Mansard Screen Enclosure; walnut travertine deck; 1 very happy kiddo.

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    wjr75's Avatar
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    Re: HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

    I think a 400kbtu heater is as big as you can get for a residential pool/spa. I have a 900 gallon 9 foot octagon and it takes around 45 to 60 minutes to heat it from a 75 degree starting temp. Are you sure when it is heating that the spa is totally isolated so all of the heat is going to the spa?
    Inground 22k gallon gunite 15x31 main pool, 15x7 wading pool/sunning deck, hot tub/with overflow (9' octagon with limestone top) & slide NSWG, Aqua Blue Pebble Sheen
    Filter dual cartridge Sta-rite 450sq/ft, TF-100 Test Kit
    Heater Raypak 2100 400k btu cupro-nickel exchanger
    Auto pool cover, Polaris 280 auto pool cleaner, Jandy AqualinkRS8 Remote Control System

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    Re: HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

    400k is as large as Ive seen from the major pool suppliers. Mahbe someone has seen larger units?
    18,000 gunite pool/spa combo. Pebble tec, iaqualink rs8, cl580 filter, aquapure 1400, 400k btu lx heater, 10 solar panels, jandy 1hp, 1 1/2hp, and 2hp stealth pumps for circ, spa, waterfall

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    Jun 2016
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    Sarasota FL
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    Re: HUGE Hot Tub taking 1.5 hours to heat 20 degrees??

    Our spa takes over an hour in the summer and sometimes 2 or more hours in the winter. We use an app on the phone to turn it on because we usually decide to use the spa while we are out to dinner.


    14k free form IG, Pebble Tec, spillover spa, IC40 SWCG, Whisperflow 1 1/2hp pump, Fafco solar, Pool Valet in-floor cleaner, Taylor K-2006 test kit

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