A HERMS brewing system recirculates mash liquid through a heat-exchanger coil in a separately heated water vessel, then returns it to the mash. HERMS stands for heat exchange recirculating mash system. The useful project is a compatible loop with controlled heating and clear measurements, not simply adding a pump and coil to an existing brewery.
Begin by deciding which process problem you want to solve: maintaining a mash temperature, supporting a planned temperature change, or improving repeatable circulation. Then design the vessels, coil, pump, fittings, measurement, and heating arrangement together. A supported modular kit can be more practical than assembling unrelated parts because they have similar threads.
Understand the three main roles
The mash vessel holds grain and liquid with a supported drainage arrangement. The heated water vessel provides the surrounding heat source for the coil. The recirculation loop carries wort through the coil and back to the mash while keeping the two liquids separate in normal operation.
The coil is a heat exchanger, not a direct immersion element inside the mash. Blichmann’s HERMS manual describes its coil operating in a hot-liquor tank with wort circulation. That manufacturer example illustrates the roles, while your actual components need their own supported instructions.
Do not assume the water bath temperature equals the whole mash temperature. Heat transfer, flow, losses, and measurement location affect the relationship. A system should let you understand those differences rather than hiding them behind one controller number.
Size the brewery around actual batches
Specify the usual finished batch volume, expected mash liquid and grain load, and the largest realistic recipe. Vessel capacity must support the relevant working volume with room for the process. A kettle’s nominal capacity does not automatically identify a compatible mash tun or hot-liquor tank size.
The coil needs to fit the intended water vessel in its supported position. Check immersion, connections, and access for cleaning. A coil that physically passes through the opening may still be unsuitable for the working liquid level or installation.
Avoid a universal coil-length or temperature-offset rule. Manufacturer performance information belongs to defined equipment and conditions. Use it to understand a supported configuration, not to promise an identical heating rate for a different vessel, pump, and batch size.
Build a compatible recirculation path
Use a pump intended for the liquid temperature and service, with fittings and tubing appropriate for wort contact and the system conditions. Follow the pump’s instructions for priming, flow management, mounting, and operation. Do not assume a general-purpose household pump is suitable because it can move water.
The grain bed must support the flow you request. Excessive draw can cause drainage difficulties in an incompatible or poorly managed mash. Choose a suitable false bottom or grain-retaining arrangement, begin under the equipment’s guidance, and observe the actual return and runoff behavior.
Keep the return gentle and positioned as the system instructions require. Hose routing should avoid kinks, strain, and unsecured hot-liquid connections. A disconnect that fits physically still needs appropriate temperature, material, and sealing compatibility.
Temperature measurement needs a purpose
Decide what each sensor measures: bath water, wort leaving the coil, mash liquid at a particular point, or another supported location. Label the readings mentally or in your records. They answer different questions and should not be treated as interchangeable temperatures.
Blichmann’s controller documentation discusses offsets and differences in HERMS operation for its configuration. That is a useful reminder that a setting may depend on the entire loop. It is not permission to copy a fixed offset into another system without observation and supported guidance.
Use a suitable independent thermometer to understand mixing and measurement differences during initial trials. Our thermometer guide covers selection. A calibrated probe can still provide an unhelpful reading if it is placed where it does not represent the process you want to control.
Heat source and controls
Choose a heating arrangement explicitly supported for the water vessel and controller. Electric installations need suitable supply, protection, and qualified work where required. Gas installations need the manufacturer’s approved outdoor location, controls, and clearances. A HERMS label does not remove ordinary heat-source requirements.
Avoid unsupported wiring or attempts to bypass protection for faster heating. Do not run an element dry or improvise around a controller fault. Follow the exact equipment’s operating and shutdown instructions, including how heating and circulation interact.
Our electric-system guide helps compare the alternative single-vessel route. If your main goal is compact temperature control, a supported all-in-one system may solve it with fewer large vessels than a custom HERMS brewery.
Separate water and wort circuits
Trace the loop clearly so the coil connections cannot be confused with unrelated water or cooling lines. A HERMS coil normally keeps circulating wort separate from the surrounding water. Inspect supported connections and component condition before relying on that separation.
Use labels or a documented diagram to make assembly repeatable. This is especially helpful when you disconnect tubing for cleaning. A setup that depends on remembering which identical hose goes where can create avoidable mistakes during a busy brew day.
Consider how you will drain each part after use and avoid leaving trapped liquid in storage. The pump, coil, valves, and tubing form one maintenance system. A clean mash vessel does not prove the recirculation path has been cleaned fully.
Cleaning should be designed before operation
Establish a routine compatible with the metals, seals, tubing, and pump. Follow cleaner concentration, temperature, contact time, and rinsing instructions. Do not assume higher concentration or heat always improves cleaning, especially where material limits differ.
Determine which components need disassembly or inspection after circulation cleaning. Residue can remain behind seals or in valves. Choose accessible service parts and obtain replacement gaskets before a worn seal becomes an urgent problem.
Compare the cleaning burden with your current routine. HERMS can provide useful control, but it adds surfaces and connections. If you do not have time or space to maintain the loop, a simpler insulated tun or BIAB method may be a better fit.
Commission with a supported trial
Before a grain batch, test the compatible system with water under the manuals’ instructions. Check leaks, pump behavior, readings, heating response, and shutdown. A trial provides useful observations without obscuring a basic fault behind a grain bed.
Then record actual behavior during a straightforward recipe: mash readings, circulation changes, heat response, and collected volumes. Do not adjust several variables simultaneously merely because a controller display differs from an independent reading. Understand the measurement locations and investigate one issue at a time.
Read mash-tun selection and BIAB alternatives before committing the budget. Build HERMS when its supported loop solves a clear need and you can maintain it. A successful project delivers understandable control and repeatability, rather than a larger collection of hardware with uncertain operating relationships.
References and editorial note
Reviewed October 3, 2026. This article explains equipment and process decisions; it is not a hands-on product test. Follow the current instructions for your exact equipment.