Above Ground Pool Plumbing Size

JKB121

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Jan 23, 2021
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Hello everyone-
I've searched for a good answer for this but have yet to find one. I have a 2 year old Doughboy 27' round pool, 54" high. It came with the standard "crappy" vacuum cleaner style 1.5" hoses. I replaced them all with 1.5" PVC pipe the first year. I added a Gulf Stream heat pump last year. The heat pump has 2" inlet and outlets. What I am trying to figure out is if I could have a more efficient system if I replaced everything with 2" PVC. Most things I read are for pools with bottom drains and multiple skimmers and returns. These pools only have 1 skimmer and 1 eyeball return.

Starting from the skimmer and going to the return, this is what I have.

-Large Doughboy skimmer with their hose connection tailpiece. I think I could get creative and enlarge this to 2" with a bulkhead fitting if it would help. It is 1.5" now.
-1.5" PVC (about 8') from skimmer to pump.
-Hayward 2 speed pump (2.25 HP) directly connected to a cartridge filter. Filter area is 175 sq. ft., maximum flow capacity 120 GPM, maximum working pressure 50 PSI. (this filter is 1.5" pipe thread only)
-1.5" PVC (about 5') to heat pump-
-Gulf Stream heat pump 122,000 BTU
-1.5" PVC (about 5') to chlorine tablet feeder.
-1.5" PVC (about 8') to return fitting on pool wall
-eyeball in return is 3/4"

On low speed the filter runs at about 4 psi. On high speed the filter runs at about 12 psi.

Does it make sense to change the filter to something with 2" pipe threads? Will adding any 2" PVC help with flow if I am restricted by the 3/4" eyeball return? I did reduce the 2" heat pump fittings to 1.5" to match the plumbing. Any suggestions to help improve flow and heat pump efficiency?
 

ajw22

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Welcome to TFP.

Changing pipe sizes will have no visible difference in flow or HP efficiency.

What are you looking to improve with your pool flow?

Using a pool cover when not in use is the best way to improve your HP efficiency.
 

JKB121

Member
Jan 23, 2021
24
Pennsylvania
Pool Size
18000
Surface
Vinyl
Welcome to TFP.

Changing pipe sizes will have no visible difference in flow or HP efficiency.

What are you looking to improve with your pool flow?

Using a pool cover when not in use is the best way to improve your HP efficiency.
Thank you for your interest in my post. Last fall I had an issue with a flow error on the new HP. I contacted them and a very helpful engineer called me back. He is leaning towards the reducing of the 2" ports to 1.5" and the 1.5" plumbing may be causing the error. At the very least, he said the HP will not be as efficient at heating the pool because it is designed to run with 2" plumbing. His estimate was that it would cost about $500.00 per season to heat the pool using my location and desired heat setting. Instead, it cost 400.00 per month to heat. He said I'm not getting all the heat out of the pump at the flow of 1.5" PVC. I'm kind of hung up on the restriction of the 3/4" eyeball. Seems like that would be a bigger problem to me.
 

ajw22

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Are you running your pump at high speed or low speed when the HP is running?

What the engineer said makes little sense to me. PVC is cheap if you want to try 2 inch plumbing. I doubt that is really your problem.

What is the GPM requirements for your HP?
 

Dirk

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Sorry, no experience with HPs, but some with a solar heater. It seems odd to me that the tech would make assumptions about optimizing your HP based on pipe size, when so many other factors can affect flow. To optimize my heater I relied on the manufacturer's suggested flow rate, and then achieved that flow rate by adjusting the RPMs of my variable speed pump while observing the flow rate using a flow meter. That's how I know I'm getting the most heat exchange out of my system.

If I didn't have a VS pump, I could use bypass plumbing to regulate flow through the heater. There will be an optimum flow rate. Too fast or too slow and you'll lose efficiency (heat exchange). Frankly, my instinct is that the guy on the phone was shooting from the hip a bit.

If you don't want to invest in a flow meter, then an alternate method of determining heater efficiency is to measure the temperature differential between before and after the heater. The difference will vary based on the efficiency of the heat exchange, controlled by the flow rate. If the manufacturer, or documentation, can't specify what the optimal differential should be, then you can experiment. Of course, with a two speed pump, you only have two choices. So to vary the flow rate, you can either mess with the size of the plumbing, or add a bypass so that you can vary the amount of water (the flow rate) through the heater.

That theory is sound, for sure, with a solar heater. I'm interpolating it for a HP. There may be better ways to optimize your heat exchange. Adjusting pipe diameter is one way, but that seems pretty limited (like your high-speed, vs low-speed choices). I'm suggesting some sort of variable adjustment, so that you can dial in the perfect flow rate and so get the most heat. A bypass is one way to do that. There may be others...
 

Dirk

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Oh, the bypass I mentioned would only reduce flow through the heater, which may or may not be what you need. You might need more flow (that isn't a given). If you don't alter the return or the skimmer, I don't see how changing the diameter of the plumbing will give you any measurable result (as Allen pointed out). Maybe a tiny bit, but not much at all. You could change the size of the eyeball, if your return fixture allows that. Or you could add a return (which would improve heating just by the fact that you'd be getting better circulation). But then you might have too much flow!

I think adding a return and a heater bypass would give you the best result: improved circulation and a way to dial in the perfect flow rate through the heater. Again, this is just my solar-heater-based logic applied to a HP, but the principles must be similar.
 

JKB121

Member
Jan 23, 2021
24
Pennsylvania
Pool Size
18000
Surface
Vinyl
Are you running your pump at high speed or low speed when the HP is running?

What the engineer said makes little sense to me. PVC is cheap if you want to try 2 inch plumbing. I doubt that is really your problem.

What is the GPM requirements for your HP?
The HP needs 30 GPM or it will shut off. They recommend running it on high speed. I've run it on low speed and high speed just to experiment. It doesn't shut off on low speed, but "seems" to heat faster on high speed. GPM requirement is 90. What was happening was a low flow error but the code also told him it was caused by too much heat in the exchanger. That's why he assumed some sort of restriction. They seem to be a reliable Company and he sent me a flow meter to install so I can give him the flow rate. Unfortunately it came a week after we closed the pool. It also is a 2" flow meter and I'm not sure it will work on 1.5". He said this HP was designed to be installed with 2" plumbing, not 1.5" I've read that max flow through 1.5" PVC is 45 GPM which is much lower than the 90 required. Even if I had 2" PVC throughout, I'm confused how I would get 90 GPM through the 3/4" eyeball return. I agree PVC is cheap, and I'd replumb with 2" in the spring if I thought it would make a difference with only one return and the eyeball restriction.
 

JKB121

Member
Jan 23, 2021
24
Pennsylvania
Pool Size
18000
Surface
Vinyl
I think adding a return and a heater bypass would give you the best result: improved circulation and a way to dial in the perfect flow rate through the heater.
Adding a return seems like a good idea, but might not be the easiest thing to do with a completely installed and functioning above ground pool. Cutting the hole with a liner installed seems tricky.
 

Dirk

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Yikes! 90 seems high, but they would know. Sounds like you're going to need 2" PVC and more returns.

My flow meter comes in sizes. And the size I have, which can work on 2" or 2.5" pipe, has two different printed scales, one for each size pipe. So I would say no, your 2" meter will not work accurately on the 1.5" pipe. Was it a FlowVis by any chance? They make a 1.5" size, though the HP company probably won't have one of those to lend.
 
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Dirk

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I've never done it, but envision pressing a large bowl to the vinyl on the pool side, while cutting a hole from the outside, then jamming the return fitting in there real quick, for a minimum of water loss. I'd love to hear that could work! I'm probably not understanding exactly what "above ground with vinyl liner" means. I'm assuming there's just one layer to go through, maybe that's not the case. Is it metal walls with the vinyl inside that? My crazy scheme might still be possible. Or just lower the water below the returns level.

The bypass would be plumbed right in front of the heater. This article describes how a bypass can be used for other purposes, but it can also be used to limit flow through the heater, by dialing it somewhere between full on and full bypass. Though from the sound of it, no limit might be needed, instead you might need all the flow you can get.

 
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JKB121

Member
Jan 23, 2021
24
Pennsylvania
Pool Size
18000
Surface
Vinyl
Yikes! 90 seems high, but they would know. Sounds like you're going to need 2" PVC and more returns.

My flow meter comes in sizes. And the size I have, which can work on 2" or 2.5" pipe, has two different printed scales, one for each size pipe. So I would say no, your 2" meter will not work accurately on the 1.5" pipe. Was it a FlowVis by any chance? They make a 1.5" size.
I don't recall the brand. I put it in with the plumbing stuff in winter storage. I guess I could either put in a section of 2" to install the meter or just buy one that fits 1.5".
 

JKB121

Member
Jan 23, 2021
24
Pennsylvania
Pool Size
18000
Surface
Vinyl
The bypass wouldn't impact the liner. But more returns would, of course. I've never done it, but envision pressing a large bowl to the vinyl on the pool side, while cutting a hole from the outside, then jamming the return fitting in there real quick, for a minimum of water loss. I'd love to hear that could work!

The bypass would be plumbed right in front of the heater. This article describes how a bypass can be used for other purposes, but it can also be used to limit flow through the heater, by dialing it somewhere between full on and full bypass.

Thanks! I'll check out the article on bypass. I think my other limitation (maybe insignificant) is that the filter is only 1.5" NPT. I'm going to have a slight restriction there unless I buy a new filter. (this one is only 2 years old).
 

Dirk

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Yikes, can of worms, right?

I think converting 1.5" to a long enough section of 2" pipe will work for the meter they sent. Don't buy a 1.5" size as it sounds like you're going to have to convert to 2" anyway. They're not cheap (like $150). Did they lend it to you, or give/sell it to you? Maybe it's not what I'm thinking of, as it's not a temporary install, it gets glued in. It's in essence a check valve. This is what a FlowVis looks like:

Screen Shot 2021-01-23 at 6.35.43 PM.png
 

JKB121

Member
Jan 23, 2021
24
Pennsylvania
Pool Size
18000
Surface
Vinyl
I'm probably not understanding exactly what "above ground with vinyl liner" means. I'm assuming there's just one layer to go through, maybe that's not the case. Is it metal walls with the vinyl inside that? My crazy scheme might still be possible. Or just lower the water below the returns level.
Yep. Metal wall with vinyl liner. I like the idea. I'm just envisioning sharp metal shavings falling between the steel wall and liner with a leak to follow....
 

JKB121

Member
Jan 23, 2021
24
Pennsylvania
Pool Size
18000
Surface
Vinyl
Did they lend it to you, or give/sell it to you?
They are a pretty good Company. They gave it to me to install permanently. I'm not sure how long of a piece of 2" pipe I would need to get an accurate reading. I'll probably start with that to see how close I am to 90 GPM. I'm sure I'm way below 90 since I can only get 45 through 1.5" pipe.
 

Dirk

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Yep. Metal wall with vinyl liner. I like the idea. I'm just envisioning sharp metal shavings falling between the steel wall and liner with a leak to follow....
Yah, risky. Lowering the water is best, but you'd still have to deal with the shavings. Hmm, can you access the backside of the metal wall? Duct tape a 3/4" block of wood behind the hole, such that the tape would trap all the sawdust and metal shavings, then use a hole saw? Then carefully remove block and tape after vacuuming the best you could? Then salad bowl and cut the liner through the hole in the wall?

I'm fairly certain no water or shavings would get anywhere near my pool, so we're good there. Give it a try! What have I got to lose?!? ;)

shopping.png

@kimkats, who do we know that knows how to cut a hole in an AG liner pool? Did you ever do that? Any trick to do it without draining any water?
 
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Dirk

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They are a pretty good Company. They gave it to me to install permanently. I'm not sure how long of a piece of 2" pipe I would need to get an accurate reading. I'll probably start with that to see how close I am to 90 GPM. I'm sure I'm way below 90 since I can only get 45 through 1.5" pipe.
Well that was very cool, especially if it's a FlowVis. Couple feet before and 1' after? Just a guess. Hmm, I know that flow is constant, so I can mount my meter anywhere in my system, even though the velocity might not be constant (like in the middle of my filter). But I'm all 2". Seems to me that if you mounted the flow meter on 2" pipe, just before the heater, that should give you the flow rate through the heater, regardless of the flow rate though 1.5" pipe elsewhere, right? Just leave enough 2" pipe exploded, before the meter and before the heater, so that you can cut it all apart and use couplers to glue the meter elsewhere if you wanted to.
 

ajw22

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You are not going to get anywhere near 90GPM. Most IG pool flow runs 30-50 GPM. Heat pumps run fine with flow slightly above what engages the pressure switch, a bit above 30 GPM.

You want to keep the water velocity below 6 ft/sec on the suction and below 8 ft/sec on the pressure side of the pump. To run at 90GPM you should have 2.5" piping.

Pipe Size6 ft/sec8 ft/sec
1.5"38 GPM51 GPM
2"63 GPM84 GPM
2.590 GPM119 GPM
3.0"138 GPM184 GPM

You have a lot in your equipment that will prevent you from running at 90 GPM including your filter. And a single skimmer can't draw water in at 90 gpm.

Give the 2" pipe a try and see what the flowmeter says your GPM is. But your AGP has a lot of inefficiencies in heating that reduce the effectiveness of your HP.
 

Dirk

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Any chance it wasn't GPM? 90 Liters/minute would be 24GPM... Or maybe 90GPM is max allowable?
 
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Dirk

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This from a Pentair Manual. Pentair heaters have a max flow limit of 120GPM (454LPM). But 24GPM (90LPM) would not be enough flow. The manual didn't mention an optimal flow rate. It shows the bypass I was describing, but they mention that only for limiting max flow, not optimizing flow rate as I suggested, so that theory might only apply to a solar heating system, not gas or HP?

Pentair Heater.png
 

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