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 PORCH TUMBLER 140 LITRE

The Porch Tumbler’s selling point is compact footprint — designed for smaller gardens, patios, or limited outdoor space. At 140 litres it sits between the Hozelock and the larger drums, which is a reasonable middle ground for a small household.

The limitations are the same as other uninsulated single-drum designs: cold composting performance, compaction risk with wet material, and batch separation issues. The “porch” positioning also implies proximity to the house, which makes the anaerobic-mess risk worth flagging — a drum that’s gone wrong is not something you want adjacent to a back door.

Functional for its intended use case. Go in with realistic timescale expectations and keep the input mix balanced to avoid the compaction problem.

At a glance

Scorecard results

Performance score 6.5 reflects a smaller capacity with limited functional gains.

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

What this bin does well

• Small footprint suits confined spaces.
• Easy turning.
• Compact tumbler for smaller gardens, restricted spaces
• Regular turning redistributes contents.

Where this bin is limited

• Low thermal mass.
• Very limited capacity.
• Low insulation.
• Turning a significant weight is not easy and puts considerable stress on frame parts.

Fit guide

Best for: users preferring compact tumbler. Not ideal if: insulated composting is desired

Build and longevity notes

Plastic drum; durability details not stated.

Practical ownership notes

limited assembly required.