Two Kettle Direct Fire Systems

Craft Hardware · Design Guide

2-Kettle Direct Fire Brewing

A space- and cost-efficient alternative to a 3-kettle system

Direct Fire Mash/Lauter Tun + Brew Kettle Kettle sizes: 40L · 60L · 85L crafthardware.de

Who This Guide Is For

This guide is intended for experienced homebrewers who want to plan and build their own 2-vessel direct fired 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 system layouts and process flows. They are not complete build guides or bills of materials.

We no longer offer custom 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 direct fire system combines the sparge water vessel and brew kettle into a single kettle, eliminating a significant portion of cost and footprint compared to a 3-kettle setup. The mash/lauter tun (MLT) has its own heating element below the false bottom, which directly heats the mash during recirculation.

This is a capable system, but it demands more attention and care than a HERMS setup. The direct heating element in the MLT creates hot spots at the base of the grain bed, and flow management becomes critical to avoid scorching. This guide covers how the system works, its honest trade-offs, and the design considerations that determine whether it runs well or causes problems.

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For experienced brewers A direct fire MLT is more demanding to operate than a HERMS system. I recommend it only for brewers who already have experience with recirculating mash systems and understand grain bed management. If you are new to recirculating systems, start with a single-kettle recirculating BIAB or a 3-kettle HERMS.

How the System Works

The 2-kettle direct fire system has two vessels:

MLT – Mash/Lauter Tun: Contains the false bottom, grain, and a heating element below the false bottom. Wort is recirculated from the MLT outlet through the pump and returned to the top of the mash. The element heats the mash directly during recirculation.
BK – Brew Kettle: Used for both sparge water storage and the boil. At the start of the brew, the BK holds all the water — both mash water and sparge water. Mash water is transferred to the MLT at strike temperature. Sparge water remains in the BK, heated to sparge temperature while the mash proceeds.

During lautering, hot sparge water is layered slowly onto the top of the mash in the MLT via the height-adjustable sparge arm. Because there is no separate HLT, the BK handles both water heating and wort collection — which means there is a brief transition period when the BK changes role from water vessel to wort receiver.

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Layering sparge water The best method for layering hot sparge water onto the denser, sugar-rich wort in the MLT is to raise the sparge arm to its maximum height before sparging. 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 contents of the kettle.

Trade-offs vs. a 3-Kettle System

✓ Advantages

Smaller footprint — two kettles fit where three cannot
Lower total cost
Fewer hose connections overall

✗ Disadvantages

Direct element in MLT creates hot spots — scorching risk if flow rate drops
Lower efficiency than a 3-kettle system of equivalent size
Reduced maximum batch size — the BK must hold both sparge water and full wort volume
High gravity or near-full-volume batches may be impractical
More valve switching required — pump inputs and outputs change roles frequently
More complex plumbing than it first appears
A controller capable of managing two elements simultaneously is needed

The efficiency and batch size limitations deserve emphasis. Because the BK must hold sparge water at the start of the brew and then receive full wort volume after lautering, the effective working volume of the BK is constrained. You may find that a 2-kettle system the same physical size as a 3-kettle system simply cannot achieve the same batch size — particularly for higher gravity beers that require large grain bills and correspondingly large water volumes.

Flow Management in the Direct Fire MLT

This is the most critical operational aspect of a direct fire system. The heating element sits below the false bottom and heats the wort at the base of the grain bed. If recirculation flow slows or stops while the element is on, the wort in direct contact with the element surface will scorch — producing harsh, permanently unpleasant flavours in the finished beer.

Follow this procedure every time without exception:

Mill grain at approximately 1 mm gap — the standard at most homebrew shops, but worth confirming. A finer crush increases the risk of a stuck grain bed.
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.
Let the grain bed rest for 3–5 minutes before restarting the pump and element. This allows the grain to 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 continuously — 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.

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Never run the heating element without adequate flow If the grain bed compacts and flow drops significantly, switch the element off immediately — before stopping the pump. Wort scorched on a dry or low-flow element cannot be fixed and will ruin the batch.

Plumbing Design

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. This allows switching between the MLT outlet (during mashing and lautering) and the BK outlet (for wort transfer and whirlpool) without moving hoses. A 3-way valve is appropriate here because you are redirecting flow between two sources, not trying to control two simultaneous flow rates — unlike the split recirculation application where separate valves are essential.

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 two kettles. For 85L kettles, use 1" fittings and 19 mm ID silicone hose throughout, with correspondingly longer extensions if needed.

Pump Outlet — Sample Valve and Drain Point

A tee with a sample valve on the pump outlet side is worth including in any direct fire build. It serves two purposes: pulling wort samples during the mash without opening hose connections, and draining the recirculation circuit between phases. Planning drain points into the build from the start makes the brew day significantly easier.

Sparge Arm as Whirlpool Arm

The height-adjustable sparge arm can eliminate the need for a dedicated whirlpool arm in the BK entirely. After lautering, move the sparge arm from the MLT to the BK upper port. Use the same arm to drive the whirlpool, and if using the 400-micron brew bag as a whole-kettle hop filter, the same recirculation path handles filtering and complete kettle drainage in one step. This removes the need for additional tees, fittings, and a separate whirlpool arm — a meaningful simplification.

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A second kettle clamp You will need a second kettle rim clamp for the sparge arm when it moves to the BK. This is available separately in the shop.

2-kettle direct fire system overview — 60L kettles — Overview of a 60L 2-kettle direct fire system.

2-kettle direct fire — pump and valve detail — The sample valve and tee at the pump outlet provides a drain point and allows wort samples during mashing.

2-kettle direct fire — sparge arm and kettle connections — Pump and 3-way valve arrangement.

2-kettle direct fire — rear view showing element and hose routing — Sparge arm positioned for lautering. The same arm moves to the BK for whirlpool after the boil.

2-kettle direct fire — front view during mashing — Front view during filling the BK.

If You Do Not Use the Brew Bag Filter Method

If you prefer a traditional whirlpool with a hop cone rather than the brew bag filter, the plumbing becomes more involved:

A 45° racking arm is required in the front lower port of the BK as the wort outlet — with its own valve. If your kettle has an additional spare port in the back, move the temperature sensor to that location.
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 MLT lower drain to the BK front outlet via the 3-way valve.

2-kettle direct fire — alternative build with racking arm and whirlpool arm — Alternative build without the brew bag filter method. A racking arm in the front BK port and a dedicated whirlpool arm add complexity and additional valve switching.

The brew bag filter approach is simpler, requires fewer fittings, and works extremely well for hop removal. 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.

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GFI/RCD protection is mandatory on every element circuit. Specify this explicitly to your electrician. A standard thermal circuit breaker is not a substitute — it does not provide ground-fault protection in a wet brewing environment.

Two Elements, Two Circuits

A 2-kettle direct fire system has two heating elements — one in the MLT and one in the BK — each requiring its own dedicated 16A circuit. Both elements must be independently switchable, as they are never both at full power simultaneously and the MLT element must be able to be cut immediately if flow drops.

Controller Requirements

You need a controller capable of managing two independent heating circuits. A single-circuit controller is not sufficient. Options include:

EINBREW 3V3P or similar dual-circuit brew controller — handles both elements with independent temperature sensing and switching, pump control, and programmable mash schedules
Two independent single-circuit controllers — one per element; simpler but requires manual coordination between the two
DIY PID build — for technically experienced brewers wanting full customisation

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Sensor placement for the MLT element The temperature sensor controlling the MLT element should be placed in the recirculation return path — in a tee at the sparge arm inlet, just before wort re-enters the mash. This gives the controller a real-time reading of wort temperature and allows it to respond before the grain bed temperature changes significantly. Placing the sensor inside the MLT body or at the pump outlet introduces lag that can lead to overshoot.

Fitting Sizes

For 40L and 60L systems: 1.5" × ¾" Tri-Clamp hose barb fittings and 14 × 24 mm silicone hose throughout.

For 85L systems: upgrade to 1" Tri-Clamp fittings and 19 × 31 mm silicone hose throughout. Do not mix fitting sizes within a system — step changes in bore create turbulence and cleaning dead zones.

Is This the Right System for You?

A 2-kettle direct fire system is a good choice if:

You are an experienced all-grain brewer already comfortable with grain bed management and recirculating systems
Space or budget makes a 3-kettle system impractical
Your typical batch sizes and gravity targets are within the capacity limits described above
You are prepared for the additional attention the direct fire MLT demands during mashing

If you are newer to recirculating systems, or if you regularly brew high gravity beers or want maximum efficiency and batch size flexibility, the 3-kettle HERMS system is the better long-term choice.

Considering a 3-kettle system?

A third kettle as a dedicated HLT eliminates the direct fire element in the MLT, removes the scorching risk, improves temperature control, and opens up larger batch sizes. Your existing kettles carry over completely — the BK stays as the BK, and the MLT becomes a true HERMS mash tun.

Read the 3-Kettle HERMS Build Guide to understand what the upgrade involves.

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