Pool Info: Pool Plumbing Pipe: Flex, Rigid, Poly
Pool plumbing is the catch-all phrase to describe the pipes, fittings and valves that carry water out of the pool to be filtered, and then return the treated water to the pool.
The most commonly used pipe for inground pool plumbing is hard PVC plastic pipe, but there also exists flexible PVC pipe, and there are some pool builders using Black Poly pipe.
Rigid PVC Pipe
There are more than 2 million miles of PVC pipe in service today, and rigid PVC pipe (Schedule 40) is the standard for pool plumbing pipe. Highly durable rigid PVC pipe is capable of a lifespan of over 75 years when properly installed.
Schedule 40 PVC pipe, 2” diameter, can hold pressure of 166 psi, whereas the thicker walled Schedule 80 PVC pipe can handle pressure up to 243 psi. Schedule 40 PVC pipe is suitable for nearly all residential pool plumbing, Schedule 80 is not commonly used on pools, mainly due to its much higher cost. Schedule 80 pipe has the same outside diameter as Schedule 40, but because it’s thicker, has a 6% smaller internal diameter.
DWV pipe, or Drain/Waste/Vent pipe, is made by wrapping a PVC foam core between two layers of solid PVC, and is meant for low pressure applications like drain pipes or in-wall home vacuum systems. Do not use Schedule 20 or Schedule 40 DWV PVC pipe or fittings in pool system plumbing.
Flex PVC Pipe
Flexible PVC pipe is made from the same polyvinyl chloride as rigid pipe, but with plasticizers added and surface ribs to allow the pipe to bend, or flex. Schedule 40 Flex PVC is available in several colors, with no material difference.
Flex pipe has several advantages over rigid PVC. It is easier and faster to install in long runs from the pool to the pump, wrapping corners and transitions easily, without the need for plumbing fittings. Flex PVC also withstands ground movement or external pressure better than rigid PVC.
Flex pipe can also withstand freezing, stretching to accommodate the nearly 10% expansion of frozen water inside of a pipe. PVC elbows or couplings however, when used to attach sections of flex pipe, can crack if water in the pipe is allowed to freeze.
On the downside however, flex pipe has a few considerable disadvantages when used for pool plumbing. The flexibility of flex pipe allows it to move slightly when under pressure. When the pump is turned on or off, this creates a slight movement in the pipe, which pulls on glue joints, coils on long runs and if sharp rocks rub against the pipe, could create leaks.
The largest criticism against using flex-pipe underground is that it can be damaged by subterranean termites or earwigs, which are attracted to the pipe, and can chew tiny holes. Especially in sandy soils, flex pipe is susceptible to insect or rodent damage.
Another large problem with flex pipe is that it is less chemically resistant than rigid PVC. Flex pipe used beneath a skimmer used for tablets, or after a chlorinator can be damaged by high chlorine and low pH levels. Harsh water alters the plasticizer resins over time, which expands to reduce internal pipe diameter, leading to an eventual clogging and crimping of the pipe.
CPVC pipe, or Chlorinated Polyvinyl Chloride is made by adding 2 chlorine atoms to the Polyvinyl chloride resin used to extrude the pipe. CPVC is rated to 200 degrees, PVC is rated to 140 degrees.
For this reason, some pool plumbers prefer to use CPVC pipe for heater and pump connections, which withstands water temperatures up to 200°. Schedule 40/80 PVC is not resistant to high water temperatures, and when exposed can melt, shrink and deform.
Using a 6” CPVC Nipple and/or a CPVC MTA fitting can fix the problem of melted (shrunken) threaded pump fittings from overheating. Similarly, using 24” CPVC pipes as heat sinks for the in/out pipes on a gas pool heater can prevent warped pipes, from heaters repeatedly shutting down before a proper cool down period.
But aside from those specific purposes, the cost of CPVC pipe and fittings can be prohibitively expensive to plumb an entire pool system.
Black Poly Pipe
High Density Polyethylene pipe or HDPE pipe is a flexible black hose used mainly on older inground pools. Joining together sections of PE pipe is done with barbed insert fittings, which are coated with Teflon pipe dope and pushed into the pipe ends, after heating the pipe with a heat gun. The joint is finished by tightening two (2) stainless steel clamps over the outside of the pipe and insert fitting.
Poly pipe has all of the advantages of Flex PVC, with greater chemical and bacteria resistance, it doesn’t attract hungry insects, and can withstand some freezing or ground movement without breaking.
Poly pipe is not without disadvantages however. The clamp connections are more likely to leak than glued PVC connections. Poly is also hard to work with in cold weather, as it loses flexibility. Rodent damage from squirrels, gophers or groundhogs has been reported.
For pools built in the 50’s and 60’s, copper pipe was used as the standard, before PVC pipe came into use.
For home plumbing, copper pipe has several advantages. Copper pipe is more earthquake resistant than PVC or CPVC, and has a melting point 5x higher than CPVC, so it won’t burn in a fire, like plastic pipe. Copper is biostatic, naturally killing bacteria.
However, copper pipes can pit, scale or corrode and is not as well insulated as PVC or CPVC, and condensate forms easily on the outside of the pipe.
But the main reason that it’s not used in pool plumbing is cost. Copper pipe and fittings are around 10x more expensive than PVC. It’s so valuable that contractors have to carefully store copper pipe to prevent jobsite theft.
Copper pipe also requires more skill and knowledge to join sections together successfully, ‘sweating’ fittings in place with a torch, flux and solder. PVC fittings are more easily glued to pipes.
What do the Markings on PVC Pipe Mean?
PVC pipe manufacturers are required to mark their pipes with information about the type of pipe, and the ASTM standards that it adheres to.
- Manufacturer name or trademark
- ASTM standard to which it conforms
- Pipe size
- Material designation code
- DWV for Drain, Waste, Vent pipe
- Pressure rating
- Schedule number
- Potable water suitability
What Size Pool PVC Pipe do I Have?
Inground pools are typically plumbed with either 1.5” or 2.0” PVC pipe. If you can find the markings on a pipe, and still read them, it will state the nominal diameter of the pipe. You can also measure the pipe, but 1.5” PVC pipe actually has an outer diameter of 1.90”, and 2” PVC pipe if measured across the pipe and ‘eyeballed’ accurately, will actually measure 2.375”. It is not uncommon to find both 2” and 1.5” pipes used on pool systems, and more complicated pools may also use smaller ¾” or 1” PVC pipe for spa overflow, chlorinator or booster pump connections. Large diameter pipe size has the advantage of lower resistance, faster water flow and lower overall system pressure.
What Type of Pool PVC Pipe do I Have?
Most inground pools will use a white color Schedule 40 PVC pipe, Type 1, Grade 1. Schedule 80 pipe and CPVC high temperature pipe is usually a gray color. Flex pipe is ribbed, flexible and comes in many colors, with no material product difference. Black Poly pipe is of course, a black color, and is identified by the use of gray clamped-on, barbed insert fittings, as opposed to glued PVC fittings.
What Type of Pool PVC Fittings Should I Use?
To join sections of PVC pipe, and to make turns or direction changes, various connectors are used such as Couplings, MTA’s, FTA’s, 90’s and 45’s. When plumbing pool systems, use only Schedule 40 PVC Pressure Fittings. DWV (Drain/Waste/Vent) fittings have only about ½” of depth to glue the pipe into, whereas pressure fittings will glue the pipe to a depth of over 1”. PVC Pressure fittings are also available, at a much higher cost, in the thicker Schedule 80 and in heat resistant CPVC, commonly used on the pool pump and heater inlet/outlets. Above ground pools often use Filter Hoses, and Hose Adapters, but could use rigid PVC if desired.
Can PVC Pipe Be Damaged by Sunlight?
Yes, like all plastic and vinyl, UV rays from the sun deplete plasticizers and resins in PVC pipe, and lead to an eventual breakdown or weakening of PVC pipe and fittings over time. For most pools with some shade over exposed pipes there is little concern. For pools in very hot and sunny areas, with full day sun exposures, manufacturers recommend painting the pipe with a water based exterior paint. Durable outdoor tapes are also available for this purpose.