plumbing design questions

cmc#5 · Feb 27, 2015

I'm in the process of determining specifications for our pool and have some questions. It'll be IG 100' circumference free form with an attached 8' diameter spa with a spillover. Depth will be 3.5 to 6. In no particular order then:

1) One or two skimmers?
2) Four pool returns? More importantly, how do these get plumbed to enable reasonably equal flow? Putting a loop around the entire pool? Split the line four ways at the equipment pad and put a ball valve on each? Other?
3) Assuming I put a bypass around the heater, how do you adjust that bypass (other than spending close to $200 on two flow meters...)
4) Two spa main drains seems like it'll be a bit tight down there but otherwise I'd be worried about potential entrapment. So what is recommended?
5) Is it ok to have the spa return through the six jets during filtration cycles or do I need a separate spa return? I'm thinking of running a VS pump so I can get away with just the one pump; low speed for filtration cycle and high speed to spa only for spa action.
6) I've read somewhere that installing a check valve just upstream of the SWCG is a good idea. True?

Thanks in advance for your comments

JasonLion · Feb 27, 2015

1) Yes

Two skimmers is nice and has become the standard these days, but one is acceptable and can sometimes save just a little on electricity with a variable speed pump).

2) Four is fine, especially if you have steps (nice to have a return for the steps), three is usually also fine. Both of the plumbing approaches you mention are fine.

3) There is certainly no need for a flow meter. Just turn up the flow until the heater is happy and then turn it up a little more. Typically a heater bypass is either all to the heater or all bypassing the heater. Heaters often have built-in bypasses these days. Not clear what you are trying to do here.

4) Two spa main drains is more or less required these days. There are alternatives, but none of them are a good idea.

5) Sure, return through the jets. You need a separate return if there are two pumps.

6) No, why would you do that? The only time you do that is if the SWG has to be right next to the heater due to space constraints.

duraleigh · Feb 27, 2015

I'll take a couple of them.....

1. 2 skimmers is better in almost every way Consider the wind direction....let the debris blow into the skimmers as much as possible.

2. Probably 3 returns is very adequate. You can loop them if you like or, easier, you can have different size eyeballs. Put the smallest one nearest the pump and increase the size as you move further away.

3. Not sure I understand. Do you need a partial bypass or simply on-off?

Can't help with the spa questions

JayBauman · Feb 27, 2015

I built a similar pool (without the spa, however) when I lived in Magnolia. Three to four return jets is adequate, but I wish I had something to keep the steps clean. With all the trees and leaves and junk, I wish I had installed a 2nd skimmer. 75% of the time, 1 was enough. However, we got crosswinds quite frequently, which caused debris to collect away from the skimmer....which ended up on the aforementioned steps. My Polaris cleaner couldn't clean the steps, so I was always doing it manually.

cmc#5 · Feb 28, 2015

The logic on the pre-SWCG check valve was you avoided any potential backflow of high chlorine water into the heater or filter where it would accelerate deterioration. I wish I remembered the source.

According to windfinder, prevailing wind at lake conroe (which is only a couple of miles north) is from the south east except for Sept to Nov when it is from the north east. The plan so far for the pool is sort of a peanut shape with the hot tub centered on one end. Imagine Mr. peanut, his hat is the hot tub lol. Lay him down with his feet pointing southwest and his head north east. Because of prevailing wind then the main skimmer would be on his right hip, ie the north west. Where would the other go? If it matters, the deep end is the hot tub side and the south west corner of the peanut will have a tanning ledge.

On the heater bypass... Full flow of the spa is ~120gpm. The point of the bypass is to not hit it with that much flow. Honestly if the filter and heater can both handle the pump's full flow rate it makes it easier.

- - - Updated - - -

Oh, and the wife is lobbying for a couple of bubblers on that tanning ledge. Something about symmetry of sound with the spillway off the hot tub haha.

JasonLion · Feb 28, 2015

cmc#5 said:
The logic on the pre-SWCG check valve was you avoided any potential backflow of high chlorine water into the heater or filter where it would accelerate deterioration.

This is true of tablet feeders, but does not apply to SWG. A tablet feeder is full of chlorine all the time, and that chlorine can diffuse backwards out of the chlorinator to the heater when the pump is off. But a SWG turns off and is chlorine free when off. There is nothing to get into the heater.

Many heaters require a bypass when the flow rate is going to exceed 100 gpm, though some of the largest ones can handle higher flow rates. If you do require a bypass due to high flow rates you would normally used a 5 or 10 lb spring check valve, which will automatically open when the flow rate is high (and thus the pressure is high).

cmc#5 · Mar 1, 2015

Ah, that explains that check valve I saw on my friend's equipment pad on the heater exit pipe. The heater I am looking at is rated for 125gpm and it has an internal bypass so I'm not worried about hitting it with full expected flow (six spa jets at 20gpm each). I am a bit worried about the flow cap without a bypass though and the heater instructions recommend installing one so I guess thats the smart move.

Speaking of which, to keep those spa jets equal do we also need a loop around the spa? That seems pretty reasonable since its not a long distance around. Start with 3" pipe at the pad? Its interesting that the pump, filter, heater all have 2 or 2.5" connections but the hydraulics page definitely recommends 3" pipe to feed those spa jets.

JasonLion · Mar 1, 2015

It is very common for the pipes feeding the spa jets to be looped around the spa. That does help keep the flow to each jet relatively uniform.

The inlet/outlet size has very little effect on water flow. The comparatively long distances the pipes run makes far more of a difference. A good rule of thumb is that it is the average pipe size that matters, not the largest or the smallest. So short segments of smaller pipe make very little difference. The exact answer is rather complex and doesn't match that perfectly, but that is a very good approximation that is easy to work with.

Yes, use 3" pipe everywhere you can for the pipes that will be in use while in spa mode, most importantly for the run from the equipment pad to the spa.