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Thread: Low speed (2 speed Tristar) enough flow for heater?

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    Low speed (2 speed Tristar) enough flow for heater?

    Does anyone know if a 2 speed 2hp Hayward Tristar pump will typically have enough water flow to operate the Hayward H-Series Universal Lo Nox Heater? This system has 2.5" PVC suction/return with about 50 foot run to pool. On low speed the Hayward Nav actually works. If the heater does not come on in low speed, can we adjust the Pressure Switch in the heater until it comes on? The pool and equipment are level. I understand that Hayward improved the flow through the Heat Exchanger, so I'm wondering then if a greater gpm is now required to create enough back pressure for the Pressure Switch. Any help here?
    POOL SPECS - 18' round AG pool Doughboy pool with 5'8" deep-end, Aqua Trol Salt Water Generator, 1HP Doughboy pump, Doughboy sand filter, Solar Dome cover and a 40'x4' solar heater. Located in Oregon with swimming season from end of May through September. I pull the pump & SWG during winter months. Solar Dome minimizes FC loss & keeps heat in & debris out. Btw - Solar Dome lasted about 6 years before plastic started shredding.

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    mas985's Avatar
    Join Date
    May 2007
    Pleasanton, CA

    Re: Low speed (2 speed Tristar) enough flow for heater?

    Most pressure switches don't require much in the way of pressure to keep closed. I have 1/2 HP two speed and the heater can work on low speed although it isn't recommended below 40 GPM. But I think in your case, low speed should be well above 40 GPM so there shouldn't be any issue. However, be aware the the temperature difference between inlet and outlet will double with low speed. So a 400k BTU heater run at 100 GPM will raise the water temperature by about 8 degrees but at low speed by 16 degrees so the water can have a much higher exit temperature.
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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