Cold Plunge Plumbing: A Layout You Can Follow

A cold plunge loop runs in one direction: tub low port, strainer, pump, filter, chiller, back to the tub high port. Add isolation valves either side of the serviceable parts, a drain at the lowest point, and keep both hoses short and insulated.

Plumbing diagrams in manuals assume you already know the vocabulary. This is the same layout written out, with the reasons behind each choice.

The loop, in order

1. Tub low port — water leaves as low as possible so debris and cold water leave with it.
2. Strainer — catches hair and grit before the pump.
3. Pump — moves water at the flow the chiller needs.
4. Filter housing — removes fines before the chiller's heat exchanger.
5. Chiller — removes heat.
6. Tub high port — returns colder water high, to mix rather than stratify.

Everything else in the diagram exists to make that loop safe to run and easy to service.

Port placement

Ports are the hardest thing to change later, so decide carefully.

• Low port as close to the bottom as possible, but high enough that the fitting does not foul the floor.
• High port at the top of the working water level, so the return does not siphon when the pump stops.
• Both ports on the same side if the chiller will sit there; this keeps hoses short.
• Reinforce the wall if the tub is thin, or use a bulkhead fitting with a wide flange.

Valves that earn their place

Three valves make a home loop liveable.

• Isolation before the pump and after the chiller: lets you service the filter without draining the tub.
• Drain at the low point: lets you empty the loop, not just the tub.
• Bypass around the chiller: optional, but useful for flushing the loop.

Ball valves with hose tails are cheap and adequate for a plunge loop.

Sizing the pipe and hose

• Use the largest diameter that fits the chiller and pump ports.
• Keep the suction run as short and as straight as possible.
• Avoid sharp elbows; use swept bends where you can.
• Insulate both runs, not just the return.

Small hoses are the most common cause of a loop that "should" deliver enough flow but does not.

A serviceable layout in plain steps

1. Drill and fit the two bulkheads with gaskets.
2. Fit the low port to the strainer.
3. Strainer to pump inlet; pump outlet to filter.
4. Filter to chiller inlet; chiller outlet to the high port.
5. Fit isolation valves either side of pump, filter and chiller.
6. Add a drain valve at the lowest point.
7. Leak test with cold water for 24 hours.
8. Insulate the hoses, then run the pump and check flow.

Common mistakes

• Returning water at the bottom, which short-circuits the mixing.
• A high port below the water line without a siphon break.
• A filter downstream of the chiller instead of upstream.
• No strainer, so the pump eats debris.
• Hoses that hang from the bulkheads and pull the fittings sideways.
• No drain, so cleaning becomes a bucket job.

If your chiller has no separate strainer

Some units include a coarse screen at the inlet. That is better than nothing and worse than a proper strainer.

• Check the screen weekly and clean it.
• Add an inline strainer upstream if the pump is external.
• Use a filter bag on the suction end as a stopgap.
• Do not remove the screen because it "keeps blocking"; find out what is blocking it.

Winterising the loop

If the tub will sit unused in a cold place, drain the loop, not just the tub. Water trapped in a pump housing or a chiller exchanger can freeze and split it.

1. Turn off and unplug the pump and chiller.
2. Drain the tub through the drain valve.
3. Disconnect hoses at the lowest points and let them drain.
4. Remove the filter cartridge and dry the housing.
5. Store the pump dry, with the impeller free.

Labelling the loop

When something goes wrong six months later, labels save an hour.

• Mark the suction and return hoses at both ends.
• Label the isolation valves with what they isolate.
• Write the pump model and the filter cartridge size inside the chiller housing door.
• Keep a photo of the finished loop on your phone.

A photo taken before the tub is filled is the fastest way to remember which hose went where. Add the date, and keep it with the manual. When you change a hose or a valve later, take another one.

Frequently asked questions

Does the filter go before or after the chiller?

Before. Filtering upstream protects the chiller's heat exchanger from debris, which is the part that is expensive to clean or replace.

Can the pump push or pull through the chiller?

Pushing through the chiller is the usual arrangement, with the pump drawing from the strainer. Confirm the chiller's flow direction if it has one.

Do I need a check valve?

A non-return valve helps if the pump sits below the water line and you want to avoid backflow, or if the return could siphon when the pump stops. It is not always required.

How high should the return port be?

Above the working water line, or fitted with a siphon break, so the tub does not drain itself when the pump stops.

Can I run the loop without a filter?

You can, but debris will reach the evaporator and flow will drop. A basic filter is the cheapest protection for the most expensive component.