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Thread: Choosing the right size heat pump

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    Bosqueboy's Avatar
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    Choosing the right size heat pump

    I've read plenty of comments on this board and elsewhere for me to decide that for a heat pump, bigger is better. The question is...at what point does it become uneconomical to get an even larger sized heat pump. For example...I used the "heat pump sizing app" on the Hayward website and it suggested for my 20,000 gal pool the 110,000 BTU pump. My guess is that if I went with that pump, it would run basically non-stop. Therefore, I should go for a larger sized heat pump that would cycle on and off and have a little extra "oompf" when needed. OK, Hayward makes 125,000 and a 140,000 BTU models. A friend, with a slightly larger pool (28,000 gal) has just installed the 140,000 BTU heater and he is as happy as a pig in mud with the way it heats his pool...without a solar blanket! With my slightly smaller pool, would I be as happy as the pig with the 125,000 unit or should I also go for the 140,000 BTU one. The price differential is minor, so that really isn't a deciding factor. I guess what I'm concerned about is whether the 140,000 unit is going to cost me more to heat the pool than the 125,000 unit. My limited supply of logic tells me that they both will cost the same, but the 140,000 unit will simply not run as long or as often. So, I should go for the larger heat pump and it will need to run for shorter periods to maintain the desired temperature. I would really appreciate any help in deciding between the 125,000 and the 140,000 BTU units.
    Bosqueboy in Virginia

    In-ground 20,000 gal vinyl Grecian, Hayward Star-Clear Plus C1200 cartridge filter, Hayward 3/4 HP Superpump, AquaRite salt water chlorine generator, Heat Siphon C575HP heat pump and Blue Diamond robotic cleaner.

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    JasonLion's Avatar
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    Re: Choosing the right size heat pump

    Get the larger one unless your are limited by budget or available amps on your electric service.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Bosqueboy's Avatar
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    Re: Choosing the right size heat pump

    The electric service being installed is 60A, so that's no problem. The price differential is just a couple of hundred, so I will most likely go with the 140,000 BTU unit. That should keep my 20,000 gals nice and warm. Now all I need is for some kind soul to send me a pdf of the service manual for the Hayward HP21404T. I'm hoping that the unit isn't a bear to work on. The typical "users manual" stuff that is available on their web site for consumers is not very helpful for a DIY guy. You have to be "in the business" to get to the good information on their web site. I would really appreciate one of you pool professionals help here. Thanks.
    Bosqueboy in Virginia

    In-ground 20,000 gal vinyl Grecian, Hayward Star-Clear Plus C1200 cartridge filter, Hayward 3/4 HP Superpump, AquaRite salt water chlorine generator, Heat Siphon C575HP heat pump and Blue Diamond robotic cleaner.

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    Re: Choosing the right size heat pump

    Your actual operating costs will be dependent on the COP, Coefficiency of Performance, rating of the unit and the BTU output. Going to a larger unit with lower COP will actually cost you more money on the heat pump operation.
    Sean Assam - Sean@teamhorner.com
    National Accounts and Commercial Products Manager
    AquaCal Heat Pumps www.aquacal.com
    AutoPilot Salt Chlorine Generators www.autopilot.com

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    Bosqueboy's Avatar
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    Re: Choosing the right size heat pump

    Yes, Sean, that is what I thought. The Hayward units that would be large enough for my pool range from the 110 K unit, the 125 K unit and the 140 K one. The COP actually is better for the larger units than for the smaller one. For the 80/80/80 measurement, the 110 K gets a 5.8 and the 140 K gets a 6.0. Likewise, for the worst measurement that they list at 50/80/63 the smaller unit rates 4.0 and the larger one rates 4.1. It seems that there is not much difference at the lower temps and humidity as you would expect as the pump technology just doesn't perform that well under those conditions.

    So, it would appear that the larger 140K unit is the best buy since it is only marginally more expensive than the smaller units. Or have I missed something?
    Bosqueboy in Virginia

    In-ground 20,000 gal vinyl Grecian, Hayward Star-Clear Plus C1200 cartridge filter, Hayward 3/4 HP Superpump, AquaRite salt water chlorine generator, Heat Siphon C575HP heat pump and Blue Diamond robotic cleaner.

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