Two Kettle HERMS Systems
2-Kettle HERMS Brewing
A space- and cost-saving alternative to a conventional 3-kettle system
Who This Guide Is For
This guide is intended for experienced homebrewers who want to plan and build their own 2-vessel HERMS system from individual components. It assumes familiarity with all-grain brewing, basic plumbing concepts, and safe handling of stainless steel fittings, valves, and silicone tubing.
The examples shown are intended solely to illustrate typical HERMS system layouts and process flows. They are not complete build guides or bills of materials.
We no longer offer custom HERMS system planning, component specification, or consultation for complete brewery builds.
Brewers without prior all-grain brewing experience should start with a simpler single-vessel system first and gain experience before moving to a 2 or 3-vessel recirculating setup.
The 2-kettle HERMS system combines the HLT and brew kettle into a single vessel, eliminating the need for a third kettle, an additional heating element, and the associated valves. The HERMS coil lives in this combined HLT/BK, and wort is recirculated through it during mashing exactly as in a 3-kettle system — with the same gentle, scorch-free heat transfer and the same temperature stability.
In a HERMS system there is no heating element in the mash kettle, so the low false bottom stand can be used and scorching is not a risk. That said, flow management still matters: a compacted grain bed can damage the false bottom or the pump regardless of how the heat is applied. A brew controller is required to hold mash temperature — manual management is not realistic.
Trade-offs vs. a 3-Kettle System
✓ Advantages
- One fewer kettle and heating element
- Smaller footprint
- Lower total cost
✗ Disadvantages
- Less efficient sparging than a 3-kettle system
- Lower batch size ceiling — BK must hold both sparge water and full wort volume
- High gravity or near-full-volume batches may not be achievable
- More frequent valve switching — pump inputs and outputs change role often
- More valves and fittings required than it first appears
- HERMS coil lives in the boil kettle — cleaning is significantly more difficult
The batch size and efficiency limitations deserve particular attention. Because the BK must hold sparge water at the start of the brew and then receive full wort volume after lautering, the effective working capacity of the BK is constrained. A 2-kettle system the same physical size as a 3-kettle system will not achieve the same batch size — this becomes a real limitation for higher gravity beers with large grain bills and correspondingly large water requirements.
The cleaning burden of the HERMS coil in the boil kettle is also worth weighing carefully. In a 3-kettle system, the coil only ever contacts clean water and requires minimal cleaning. In a 2-kettle system, the coil is exposed to wort during the boil and to hop material if hops are added directly to the kettle. A 400-micron brew bag used as a whole-kettle filter keeps hops away from the coil and is strongly recommended.
Flow Management
As with all recirculating systems, grain bed management is critical. Follow this procedure every time:
- Mill grain at approximately 1 mm gap — the standard at most homebrew shops, but worth confirming.
- For grain bills with high proportions of wheat, oats, or rye, add rice hulls to improve drainage and prevent compaction.
- Switch the pump off before adding grain. Ensure the heating element is also off at this point.
- Stir the grain in thoroughly — no dry clumps or pockets.
- Allow a 3–5 minute grain rest before restarting the pump and element. This lets the grain swell and settle naturally.
- Almost close the pump outlet valve, restart the pump, then open the valve very slowly. Opening too fast compacts the grain bed immediately. Once flow is stable, switch the heating element on.
- Do not leave the system unattended. Monitor the MLT liquid level — if it rises during recirculation, negative pressure is building under the false bottom. Stop the pump immediately and stir to break up the grain bed.
Design Considerations
Temperature Sensor Placement
Place the controller temperature sensor at the return point of the recirculation loop — in a tee at the sparge arm inlet, just before wort re-enters the mash. This is the correct position to prevent temperature overshooting or oscillating. Placing the sensor inside the HLT/BK body or at the MLT outlet introduces lag that leads to unstable control.
Layering Sparge Water
At the end of mashing, hot sparge water must be layered carefully onto the denser, sugar-rich wort in the MLT. The best method is to raise the sparge arm to its maximum height before beginning the sparge. The height-adjustable sparge arm makes this straightforward. A fixed sparge arm can work but requires very slow filling and careful attention to avoid mixing the kettle contents.
Sparge Arm as Whirlpool Arm
Used properly, the height-adjustable sparge arm can eliminate the need for a dedicated whirlpool arm in the boil kettle entirely, reducing the additional tubing, fittings, and splitters required at the pump outlet. To fill the boil kettle during lautering, simply move the sparge arm from the MLT to the BK. The same arm then drives the whirlpool, and when used with the 400-micron brew bag as a whole-kettle filter, the same recirculation path handles hop filtration and complete kettle drainage in one step. A second kettle rim clamp for the sparge arm is available separately in the shop.
Pump Inlet — the 3-Way Valve Approach
The most practical way to connect both kettle outlets to the single pump inlet is via a 3-way ball valve, allowing switching between MLT and BK without moving hoses. Connection example for 60L kettles: two 15 cm stainless extension tubes connect each kettle outlet to the 3-way valve, with a 10 cm extension positioning the pump in front of and between the kettles. For 85L kettles, use 1" fittings and 19 mm ID silicone hose throughout.
Pump Outlet — Sample Valve and Drain Point
A tee with a sample valve on the pump outlet side is worth including in any 2-kettle build. It allows wort samples during mashing without opening hose connections, and provides a convenient drain point for emptying the recirculation circuit between phases. Planning drain points into the build from the start makes the brew day significantly easier.
Bypassing the HERMS Coil During Lautering and Whirlpool
When lautering into the boil kettle and during the whirlpool, connect the hose to bypass the HERMS coil. By this point the coil has already been cleaned on the inside by the sparge water passing through it during the mash, so bypassing it for wort transfer and whirlpool keeps the circuit as simple as possible and avoids exposing the coil to hop-laden wort unnecessarily.
When lautering into the boil kettle and during the whirlpool, connect the hose to bypass the HERMS spiral. Shown here filtering the kettle after boiling with the 400-micron brew bag as a whole-kettle filter:
If You Do Not Use the Brew Bag Filter Method
If you prefer a traditional whirlpool rather than the brew bag filter, the plumbing becomes more involved:
- A 45° racking arm is required in the front lower port of the boil kettle as the wort outlet — with its own valve. If your kettle has a spare port at the rear, relocate the temperature sensor there to compensate for the lost front port.
- A dedicated whirlpool arm is needed in the BK upper port.
- An additional 3-way valve at the pump outlet avoids a hose swap when switching from mash recirculation to BK filling.
- At minimum one flexible silicone hose connecting the bottom drain of the MLT to the front port of the boil kettle.
Or like this:
Shown here with 85L kettles:
The brew bag filter approach is simpler, requires fewer fittings, and works extremely well for hop removal and hot trub separation. The traditional whirlpool route is only worth pursuing if you have a specific reason to prefer it.
Electrical & Controls
Craft Hardware heating elements are sold unwired. All electrical connections must be made by a licensed electrician before use. Every heating element circuit must be protected by a GFI/RCD breaker.
The 2-kettle HERMS system has one heating element in the combined HLT/BK requiring a dedicated 16A circuit. The 85L system has two elements and will need a controller suitable for controlling multiple elements together. Two independent single-circuit controllers are also an option but require manual coordination.
Is This the Right System for You?
A 2-kettle HERMS system is a good choice if space or budget makes a 3-kettle system impractical, your typical batch sizes and gravity targets are within the capacity limits of the system, and you are comfortable with the added valve complexity and the cleaning demands of the HERMS coil in the boil kettle.
If you regularly brew high gravity beers, need maximum batch size flexibility, or want the simplest possible cleaning routine, the 3-kettle HERMS system is the better long-term choice.
Considering a 3-kettle system?
Adding a dedicated HLT moves the HERMS coil out of the boil kettle and into a vessel that only ever holds clean water. Cleaning becomes trivial, batch sizes increase, and sparging efficiency improves. Your existing two kettles carry over completely — nothing is wasted.
Read the 3-Kettle HERMS Build Guide to understand what the system involves.