Install
Water Softener Loop Explained
A water softener loop is a pair of pre-plumbed pipes, usually with a drain stub beside them, that a builder runs out of the wall so a softener can be connected later without cutting into the main line.
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Quick answer
- A loop is two supply pipes out of the wall, often with a drain.
- The builder chooses which fixtures sit downstream of it.
- Crack the main open: the pipe that flows is the inlet.
- No loop means cutting into the main line, or hiring a pro.
What a softener loop is
When a house is built, the plumber can route the main water line out to a convenient spot, then back into the wall, before it continues to the fixtures. That out-and-back section is the softener loop. SoftPro's Elite install guide describes a typical pre-installed loop as two pipes coming out of the wall, plus a third pipe for the softener's drain.
Until a softener goes in, the two pipe ends are usually joined so water can flow straight through. When you add a softener, that connection comes out and the softener's bypass and control valve take its place. One pipe becomes the inlet, carrying water from the supply to the softener, and the other becomes the outlet, carrying softened water back to the house.
Builders add a loop for two reasons. It puts the connection somewhere with space, such as a garage wall or a utility room, and it lets them decide which lines are softened. Lines that branch off the main before the loop stay on hard water, which suits outside faucets and irrigation; in Pentair's 5600SXT plumbing drawing the hose faucets are fed unsoftened water, and the Virginia extension service sees no need to soften water used outdoors. Whether your builder did this depends on the house, so check before you assume.
How to find yours
Look where builders tend to put loops: on a garage wall, in a utility or laundry room, or in the basement near where the main enters the house. Signs that you have one:
- Two capped or joined pipes coming out of the wall side by side, at about the same height, often with a short connecting section between them.
- A drain stub nearby, which SoftPro's guide describes as the usual third pipe.
- An outlet within reach, since the softener needs power.
- Labels such as "softener" or "inlet" and "outlet" written on the wall or pipes by the builder.
If the two pipes run into the wall and you cannot tell which way water flows, SoftPro's guide gives a simple test once the loop is cut open: with the pipes open and a bucket ready, open the main just a little. Water will come out of the supply pipe, and that one goes to the softener's inlet; the dry one is the outlet.
Not every pair of pipes is a softener loop. Before cutting, shut off the main and confirm the pipes are on the main supply line, not a branch to one fixture. If you are unsure, a plumber can confirm it quickly.
Connecting a softener to a loop
With a loop in place, the job is mostly connection work. Our installation guide has the full sequence; here is how it applies to a loop.
- Shut off the main and drain the line. Open a low faucet to relieve the pressure.
- Open the loop. Remove the connecting section between the two pipe ends, keeping cuts square and clean.
- Identify inlet and outlet. Use SoftPro's cracked-main test above, then shut the main again.
- Fit the bypass and connectors. For a SoftPro Elite, quick connect hoses link the loop pipes to the valve; on a Fleck, QWT's guide pairs push-fit connectors with copper, PEX or CPVC and solvent cement with PVC. See the bypass valve guide.
- Keep the ground. If plastic fittings now break a metal pipe run, Quality Water Treatment calls for an approved ground clamp with at least #6 copper wire across the gap.
- Connect the drain. Run 1/2-inch tubing to the drain stub or another approved drain, ending above it with an air gap. Tubing size and how high it can climb are on the drain line page.
- Start up and program. Follow your system's start-up steps, then set hardness and regeneration with our settings guide.
A loop on a well home should still sit after the pressure tank, since SoftPro's Elite guide says the softener will not work properly before it. On most well homes the main runs from the pressure tank to the loop, but confirm it on yours.
Homes without a loop
No loop is common in older houses, and it does not stop you from installing a softener. Quality Water Treatment's guide says that if no soft-water loop exists, install one from the main supply line before it enters the home, or have a professional install one.
In practice that means choosing a spot on the main, after any pressure tank and filters and before the water heater, then cutting in and running pipe to and from the softener. The placement rules explain the order of equipment on the main, and installation cost shows how much a missing loop can add to a plumber's bill.
Plan which branches you want on hard water before you cut. Lines that leave the main ahead of the new connection stay hard; anything after it gets softened.
Common questions
What does the third pipe next to a softener loop do?
In SoftPro's description of a typical loop, the third pipe is the drain for the softener. Run the drain tubing to it with an air gap at the top, rather than pushing the tube inside.
Does a softener loop include the outside faucets?
Often not, because builders tend to branch outdoor lines off before the loop, and outdoor water does not need softening. Run an outside tap and test it for hardness after install to find out for sure.
Can a loop be added to an existing house?
Yes. Quality Water Treatment says to install one from the main supply line before it enters the home, or to have a professional do it. Expect more work if the main is hard to reach.
Which loop pipe is the inlet?
The supply side. Following SoftPro's method, cut the loop, ease the main open a fraction, and watch for water; whichever pipe runs feeds the softener's inlet port.
Related guides
More help: see our guide to water softener care.