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Thread: Spa Size & Heater Size

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    Spa Size & Heater Size

    I'm in Florida and I'm considering building a 40 square foot round spa attached to a pool with 6 jets and a 250K BTU heater. How many adults would I comfortably be able to fit in a spa this size? Is 250K BTU going to be sufficient to heat a spa of this size? Is a Pentair VS3050 going to be enough to drive the spa and a 17x37 pool or should I have an additional pump for the spa?

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    Join Date
    Mar 2012
    Tampa Bay, Florida

    Re: Spa Size & Heater Size

    That is about an 8 ft diameter tub and is the same size I have. I can get 8 to 10 people around mine all sitting on an outside circular seat, but these folks better be good friends . I wouldn't see a problem with 4 or 5 (or even 6) close couples. Your heater size should be fine and I hope it is natural gas (for cost control).
    I have a slightly smaller size propane heater and get a little better than 10 to 15 degrees rise every 30 to 45 minutes. Newer heaters are much more efficient than my old 1970's unit.

    EDIT: I have a seperate pump and filter for the spa and recommend you go that way. Add a blower (bubbler) too. When you have a number of people in a warm or hot spa, it needs filtering as much as, if not more than a pool since you have a much greater concentration of contamination per volume of water. Get a good DE filter and you'll be glad you did. Right now, I use my spa more than the pool. I was in it stretching and drinking a cup of coffee before work this morning, gazing up at the stars. Life is Good! . You will enjoy the investment!
    John (DIYer). Concrete, approximately 13,000 gallon in-ground pool with adjoining concrete spa. Approximately 40 years old. Hayward Super II pump for pool and legacy Anthony Sta-Rite bronze pump CF6 for spa, VA-26 filter,(2 sets), Rheem propane heater for spa. HASA Liquidator for pool.

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    mas985's Avatar
    Join Date
    May 2007
    Pleasanton, CA

    Re: Spa Size & Heater Size

    40 sq-ft is 7' round diameter and 10 people would be pushing it. Even 8 is a little cozy. Plus most everyone will want their own spa jet so I would say 6 people is a practical limit.

    As for heater size, I would go with a 400k BTU heater which is what I have. This will increase the speed at which the spa is brought up to temperature so there isn't as much wait time for the spa to get hot.

    As for a pump, the plumbing will need to go through the filter and heater both of which add a lot of restriction. Depending on the head loss in the equipment, the VS may or may not be able to provide enough flow rate for the jets so you might want to also have a bypass built into the pad just in case. In most cases, I prefer to have a separate pump on separate plumbing for this reason.

    Forgot to mention that I would go with the new VS (011018) over the 3050. They are about the same price but the new VS has several more features.
    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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