Whirlpool Arm Construction for Kettle

Last updated: May 14, 2026

A whirlpool arm creates the tangential flow that causes wort to spin in the kettle, concentrating trub, hop material, and protein precipitate into a compact cone at the kettle center. I added a welded whirlpool arm to my boil kettle after years of dealing with clogged pump intakes and cloudy wort transfers, the improvement in trub separation was immediate and dramatic. With a properly constructed whirlpool arm, I can transfer 90% of a batch while leaving a clean trub cone in the kettle. Construction is a simple welding project that any homebrewer with basic TIG skills can complete in an afternoon.

Whirlpool physics in the brewing kettle

A whirlpool works on the “tea leaf paradox” described by Einstein: tangential flow in a cylindrical vessel creates a toroidal (donut-shaped) secondary circulation that drives particles toward the center bottom of the vessel. The primary tangential flow spins the liquid; centrifugal force pushes liquid outward near the surface; the outward flow then cascades down the vessel walls and returns inward along the bottom, carrying trub particles toward the center. For effective separation, the kettle must be cylindrical (not conical), the wort must be spun at sufficient velocity to establish the circulation pattern, and then left undisturbed for 10–15 minutes for the trub cone to compact and settle.

Whirlpool arm design specifications

Inlet positioning

The whirlpool arm inlet connects to the kettle wall through a TC fitting at mid-height, approximately 1/3 to 1/2 up from the kettle bottom. This height keeps the inlet above the expected trub cone while still low enough to create effective circulation throughout the wort column. The arm should extend horizontally toward the kettle center, then turn 90° to direct flow tangentially (parallel to the kettle wall, not toward the center). The outlet of the arm should be positioned 1–2″ from the kettle wall, and flow should be directed in the same rotational direction for all arms (if using multiple).

Tube diameter and flow rate

For a homebrewing kettle (15–30 gallons), a 1/2″ OD stainless tube arm with pump flow of 4–8 GPM produces effective whirlpool velocity. Too small a tube at high flow creates backpressure that strains the pump; too large reduces velocity at the outlet. A 1/2″ tube at 6 GPM gives an outlet velocity of approximately 3–4 ft/s, which is adequate for a 15-gallon kettle. Larger kettles benefit from 3/4″ tube at higher flow rates.

Construction steps

1. Measure your kettle interior diameter. The horizontal arm should reach from the wall to approximately 1/3 of the way toward the center, do not extend past the center, as this disrupts the circulation pattern.
2. Cut the arm from 1/2″ OD 316 stainless tube. Bend the outlet end 90° using a tube bender. The outlet should face tangentially, parallel to the kettle wall, not inward.
3. Drill a hole in the kettle wall at mid-height for the arm. Install a 1.5″ TC weldless fitting or TIG weld a 1.5″ TC ferrule to the kettle wall.
4. Fabricate a TC adapter that accepts the 1/2″ tube, a 1.5″ TC cap with a 1/2″ NPT fitting compression-sealed to the tube, or a custom welded adapter.
5. Insert the arm through the fitting, position the outlet tangentially, and lock in place.
6. Connect the pump return line to the whirlpool arm inlet and test with water at full pump flow, watching for even rotation and no turbulence at the outlet.

Using the whirlpool effectively

1. At flameout, engage the pump to recirculate wort through the whirlpool arm for 5–10 minutes.
2. For hop additions that benefit from whirlpool temperatures: recirculate for 15–20 minutes with the lid on to maintain temperature, adding hops at the appropriate temperature (170–185°F for high-aromatic additions, flameout for bittering).
3. Shut off the pump and let the wort rest undisturbed for 10–15 minutes. The circulation pattern will settle into a compact trub cone at the center bottom.
4. Transfer wort by opening the kettle drain valve slowly. Transfer from the wall side (where wort is clear) rather than center-bottom where trub has collected.

Common Questions

Does a whirlpool work with hop pellets?

Hop pellets work well with whirlpool separation, pellet hop material breaks down into small particles that compact effectively into the trub cone. Whole leaf hops do not respond well to whirlpool separation because the leaf structure creates a floating mat rather than a compact cone; use a hop spider or hop bag for whole leaf additions. For pellet-heavy late hop additions, the trub cone will be larger and softer, extend the settling time to 15–20 minutes before transferring. Some homebrewers use a hop filter tube (a perforated stainless pipe at the kettle drain) as a secondary filter for pellet hop debris that the whirlpool doesn’t compact completely.