Compost-Bins.co.uk

Summary

During my development of the HOTBIN composter, I built and tested several rotating drum prototypes before abandoning the approach entirely. That decision wasn’t arbitrary — it came from working through the engineering with Professor Haug’s composting engineering handbook as a reference, and from cleaning out more than one compressed anaerobic mess.

Four specific problems killed the tumbler concept for me.

First, aeration. Turning is supposed to introduce oxygen — and it does, briefly. But the dynamics of how much air actually enters relative to the material being moved are poor. The best data I could model suggested the introduced air lasts minutes at most before it’s consumed or displaced. Unless you’re prepared to turn continuously, passive buoyant airflow through a static aerated bin delivers more oxygen more consistently, with no effort.

Second, compaction. When a tumbler rotates, material is scooped to the top and drops to the base. Fins help, but only partially. In practice — and I’ve experienced this firsthand — the repeated drop compresses wet material into a dense ball. Instead of aerating, you’ve created exactly the conditions for anaerobic breakdown: a compressed, airless mass that goes smelly and stalls. It’s the opposite of the intended effect.

Third, batch separation. You cannot easily turn out finished compost without emptying the whole drum — which means mixing old and new material. The twin-tub designs partially address this, but only partially.

Fourth, weight. Any decent-sized bin quickly gets to +40 Kg. That is a significant weight to move manually and puts strain on all components.

I haven’t had any of the following bins on site for extended testing. But I’ve been inside the engineering problem they’re trying to solve, and that’s the lens I’m applying here.

MANTIS BACKYARD TUMBLER 335 LITRE

The largest tumbler in this review set, and the one where the volume argument works most in the tumbler’s favour. At 335 litres there’s enough material mass that heat generation during active periods is more sustained than in smaller drums — not hot composter sustained, but meaningfully better than a 100-litre drum.

The single-drum design means batch separation remains an issue. And at this size, the weight of a fully loaded drum makes rotation physically demanding — worth factoring in if regular turning is part of the intended workflow.

The size is the best thing about it. If you want tumbler convenience at meaningful volume and accept cold composting timescales, this is the strongest single-drum option in the set. For comparable output from a static insulated bin you’d be looking at something like the HOTBIN 200 in a fraction of the footprint.

At a glance

Scorecard results

Performance score 6.4 reflects a large capacity but limited functional gains.

Value for Money score is ‘poor’, reflecting the high price versus functionality.

What this bin does well

• Larger capacity than compact tumblers.
• Regular turning redistributes contents.

Where this bin is limited

• Low insulation.
• Turning a significant weight is not easy and puts considerable stress on frame parts.

Fit guide

Best for: users preferring tumblers with more capacity Consider if: space allows Not ideal if: insulated composting is desired

Build and longevity notes

Metal drum; durability details not stated.

Practical ownership notes

Assembly required.

What we couldn’t verify

• Warranty

Summary

A large capacity tumbler balancing handling and volume.