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A RIMS (Recirculating Infusion Mash System) tube is the heart of any direct-fire mash heating system, it’s a stainless tube with a heating element inside that wort flows through continuously during mashing, keeping the mash at precise temperature without the thermal mass of a hot liquor tank. I built my first RIMS tube from a 2″ stainless pipe with a 1500W electric element, and the temperature control it provided was dramatically better than my old infusion method. Getting heat distribution right in the tube design is what separates a RIMS that scorches wort from one that holds steady temperatures cleanly.
RIMS tube fundamentals
A RIMS tube heats wort by flowing it past an electric resistance element inside a sealed tube. The element heats the wort as it passes, and the PID controller cycles the element on and off to maintain target temperature. The critical design requirement: the wort must always be flowing past the element when it’s energized. Stagnant wort in contact with a hot element scorches in seconds, burnt protein will coat the element, ruin wort flavor, and eventually destroy the element. Flow rate and element wattage must be matched to prevent localized overheating.
Heat distribution design parameters
Element watt density
Low-watt-density (LWD) elements are critical for RIMS, standard water heater elements run at 40–80 W/in² and will scorch wort. Brewing-specific LWD elements (Bru’n Water, Spike, etc.) run at 15–25 W/in², distributing heat over a much larger surface area at lower temperature. A 1500W LWD element in a 2″ tube at 1 GPM flow rate will raise wort temperature approximately 8–10°F per pass without approaching scorching temperatures at the element surface. Higher wattage requires proportionally higher flow rate to maintain the same element surface temperature.
Tube geometry and flow velocity
The tube inner diameter determines flow velocity for a given pump flow rate. Minimum recommended flow: 0.5 GPM. Optimal: 1–2 GPM. A 1.5″ tube at 1 GPM gives ~0.2 ft/s velocity; a 2″ tube at 1 GPM gives ~0.1 ft/s, both are adequate. The element should occupy 60–80% of the tube length with at least 2″ of clear tube on each end for flow turbulence to normalize before the outlet. Mount the element horizontally or at a slight downward angle toward the outlet so any grain particles that enter don’t rest against the element.
PID SSR duty cycle
A solid-state relay (SSR) controls the RIMS element via PWM from the PID. With a 2-second cycle time and a PID at 50% output, the element fires for 1 second on, 1 second off. At 50% duty cycle, a 1500W element is effectively 750W average, lower heat input reduces scorching risk. Autotune the PID with actual mash recirculation running to get stable tuning parameters; PID settings tuned on water only will overshoot badly on wort due to the viscosity and specific heat difference.
RIMS tube construction
- Cut a 12–18″ length of 1.5″ or 2″ schedule 10 stainless pipe for the tube body.
- Weld or use threaded end caps. One end gets a 1.5″ TC ferrule for inlet; the other gets a TC ferrule for outlet.
- Drill and tap the inlet end cap for a 1″ NPT element fitting (or use a weldless element fitting with gasket). The element enters from the inlet end and terminates 2″ from the outlet end cap.
- Install the LWD heating element and seal with a food-grade gasket and compression fitting.
- Install a 1/4″ NPT thermocouple probe fitting in the outlet end cap, the probe reads wort temperature immediately after the element for accurate PID feedback.
- Test water-only at full flow and full element power for 10 minutes before first use with wort.
Common Questions
What flow rate should I run through the RIMS tube?
Run the highest flow rate your pump and grain bed can support without setting the grain bed. For a 10–15 gallon homebrew system, 1–1.5 GPM is typical. Higher flow rates give better heat distribution and lower element surface temperature for the same heat input, reducing scorching risk. The limiting factor is usually the mash tun grain bed, too fast and the wort runs cloudy or the grain bed compacts and flow drops to nearly zero. Start at 0.75 GPM and increase until you see grain bed disturbance, then back off 25%. A vorlauf of 5–10 minutes before setting your target mash temp helps establish grain bed stability for consistent RIMS flow.
