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Thread: Number of skimmers and bottom returns

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    Number of skimmers and bottom returns

    I am in the process of building a pool in NJ, but haven't picked my PB yet. My pool will be about 1200 square feet, have a variable speed Jandy E pump, an Aqua Comfort AC-150 Heat Pump, a Polaris 280 with 3/4 booster, a Rockwall and Grotto (inside Grotto there will be 6 Jacuzzi jets and blower), 2 Laminar Jets, 2 LED Bubblers in a sunshelf, 2 Ledlights in pool and one in Grotto, Jandy PDA P8 remote control, 90% Quartz finish, Zodiac SWF 185 GMP waterfall pump, Levelor K1100 autofill, and Autopilot Digital SWG. My pool will have 2 skimmers and (as of now) 5 returns. Most piping is 3 inch (and I think all returns and skimmers are home runs).

    One PB refuses to put in bottom returns, which I thought would help heat the pool. But two other pool builders actually suggested them. Do you think not having bottom returns is a big detriment? Also, do you think a pool this size should have three skimmers or is two sufficient?

    Thanks

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    mas985's Avatar
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    Re: Number of skimmers and bottom returns

    What exactly do you mean by bottom returns? Are they in the floor of the pool or are they just lower returns on the wall. The later would be better than the former. I don't like the idea of putting anything on the pool floor. But you can accomplish the same thing with standard returns pointed downward.


    This is a bit off topic but why are you deliberately putting in a blower until you know if you need one. A properly designed spa should not need a blower. They are mostly used to compensate for a bad design.
    Mark
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    Re: Number of skimmers and bottom returns

    I think the returns suggested by a couple PBs were infloor, but I'll have to check.

    For the Blower, I never actually asked for it, but it was part of the packlage that the PBs were giving me. It is much easier to just accept it, than try to get a credit for it at this point.

    Any opinion on how many Skimmers I should have in the pool?

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    mas985's Avatar
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    Re: Number of skimmers and bottom returns

    I am not sure having three skimmers would buy you much especially if the the wind is primarily from one direction. I have two skimmers but one gets most of the debris because of the wind. Also, another problem with increasing the number of skimmers is the flow rate is split between the skimmers so for a given flow rate each skimmer has reduced flow rate and reduced skimming ability. This will force you to higher flow rates and more expensive run time. The only exception might be due to the shape of the pool.
    Mark
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    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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    Re: Number of skimmers and bottom returns

    So if I wanted a flow rate of 60 gpm (I am just guessing), each skimmer would have a flow rate of 30 GPM (if I had 2 sklmmers) and 20 GPM if I had three? What does that mean exactly? Does each skimmer pickup less debris? I don't have a good handle on flow rates (or much of anythign else to do with a pool for that matter).

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    Mod Squad jblizzle's Avatar
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    Re: Number of skimmers and bottom returns

    It means that each will not skim the surface as well when the flow rate is lower. And as he said, which ever skimmer is downwind will be picking up the most debris. If the winds are typically only in one direction, then you really would only need 1 skimmer. But if variable winds then a second skimmer could be helpful.
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    Re: Number of skimmers and bottom returns

    I've got in-floor returns. Only 3 returns, all in-floor. Just plain, ol' returns, not some kind of in-floor cleaning system. This is my third inground pool, the first w/ in-floor returns, and I've never seen any difference between in-wall & in-floor. 20 years with this pool and I've never said, "I wish I didn't have in-floor returns."

    Just another pool owner here and I know others may have different experiences.

    Good luck!
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    Re: Number of skimmers and bottom returns

    Quote Originally Posted by CUTiger78 View Post
    I've got in-floor returns. Only 3 returns, all in-floor. Just plain, ol' returns, not some kind of in-floor cleaning system. This is my third inground pool, the first w/ in-floor returns, and I've never seen any difference between in-wall & in-floor. 20 years with this pool and I've never said, "I wish I didn't have in-floor returns."

    Just another pool owner here and I know others may have different experiences.


    Good luck!
    Thank you for sharing CUTiger, I am in the middle of my pool build and I am putting in (in-floor) returns as well. I was just checking around just to make sure I wasn't half crazy for placing them there on the bottom as well. I am feeling a tad more confident I am doing the correct configuration for my pool build, thanks.


    BTW~ GrottoGuy, I am building a rather large pool myself and I am only installing 2 skimmers. At first I was going to put in more however, after learning from everyone here I scaled back to the two. I think it's better all around to think about just going with 2 skimmers. But I am certainly not an expert by no means.
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    Richard320's Avatar
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    Re: Number of skimmers and bottom returns

    Quote Originally Posted by grottoguy View Post
    So if I wanted a flow rate of 60 gpm (I am just guessing), each skimmer would have a flow rate of 30 GPM (if I had 2 sklmmers) and 20 GPM if I had three? What does that mean exactly? Does each skimmer pickup less debris? I don't have a good handle on flow rates (or much of anythign else to do with a pool for that matter).
    20 GPM is 4620 in3/minute getting sucked out of the pool to the filter. Since water seeks its own level, it will flow towards the skimmer to replace what's been pulled out. If the skimmer opening is 20 inches wide and the water over the weir is half an inch deep, that's 10 in2 so 462 inches/minute or 7.7 inches per second.

    Let's say a leaf is drifting past driven by the flow from the returns at ten inches per second. The pull from the skimmer may not be enough to alter its course and draw it in - it will go right past the skimmer. But if the return is pulling 30 gpm, the flow is 11.5 which should be enough to pull that leaf in.

    Visualize a sink full of shaving cream film and beard stubble. If the drain is clear, it empties fast and there's very little residual left. If it's clogged with hair and it drains slowly, there's a lot of stuff left in the sink. The pool is the same way just on a bigger scale. You want to carry the scum on the surface away to be filtered out.

    The most important thing is to have the skimmer be at the extreme downwind end of the pool. If, like my pool, the skimmer is ninety degrees to the prevailing wind, the slightest breeze will overpower the pull of the skimmer and everything goes right past and clumps against the far end until it gets waterlogged and sinks, where I get to vacuum it.
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    Re: Number of skimmers and bottom returns

    My skimmer is joined to the main drain underneath the basket and after lots of experimentation I found I needed 50 gpm to get it to work well.

    I wish the pool had been built with a seperate line from the main drain so I could reduce the gpm needed for skimming.

    IMHO correct positioning of the returns to avoid surface water dead spots should eliminate the need for a second skimmer, and would enable you to cut back on gpm and significantly reduce pump power costs.

    +1 on locating the skimmer downwind. I bet my skimmer time could be cut in half if mine was downwind !!!

    Also I don't know how bottom returns would work on directing surface debris towards the skimmer, but I suspect wall returns would be better.
    Cheers, Peter
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    Re: Number of skimmers and bottom returns

    If it was my pool, I would use two skimmers with, as mas985 says, the downwind location being the most important parameter. 1 skimmer is not enough f0or a pool that big and 3 would probably reduce the flow of each so that none of the three are particularly effective.

    I am really parroting what mas985 posted just for emphasis.

    Side wall or in-floor location of return will have no effect on heating the pool either way.
    Dave S.
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