Tumbler (rotary compost bins) compared to the HOTBIN

26 March 2014  |  HOTBIN Composting

If you are deciding whether to buy a tumbler compost bin or the HOTBIN, here is a quick expert recommendation and a more detailed list of considerations to enable you to evaluate the type of compost bin for yourself.

Our expert recommendation: As soon as you set a goal to compost all food waste (including meat, leftovers, bread, pasta, etc), and you want to compost all year round (through winter), with no vermin, flies or odour, then you need to opt for a specialist hot composting bin. Many tumblers are not capable of hot composting and if you hot compost and use a bulking agent there is actually no need to turn your compost.

To establish if a product is "better" you need to take a step back and ask with respect to what?

What am i trying to achieve?

There are two sets of features to look at. The first group looks at whether you want to hot or cold compost, and the second group look at how easy the compost bin is to use.

Group 1 – Hot or cold composting? Do you want to:

  • Compost ALL food waste from a typical domestic home
  • Compost all year round (ie through winter)
  • Compost faster - typically  less than three months
  • Compost difficult garden wastes (eg weed seeds, couch grass, etc)
  • Compost without rats, flies or odour
  • Compost without turning (fork over the heap)
Vendors will try and persuade you their bin will do 'a lot' and you can 'control things'. To a degree this is true - but there is a huge performance gap between a bin designed to hot compost and a tumbler that holds waste while it cold composts.

To hot compost you need to:

  1. Feed it the right mix of chopped up waste
  2. Retain heat - ie insulate it by using specialist insulating materials
  3. Aerate - harness the science of buoyant airflow to get air to each bacterium at microscopic level
  4. Control water - remove excess water from the mix
  5. Enclose the waste, remove odours and control vermin and flies
The items are connected - get all five right and it is a virtuous circle, get one wrong and it can quickly form a vicious circle, spiralling downwards out of control.

1. Feed It - Some materials compost faster than others. Feeding chopped up, 'easy to digest' waste allows fast digest and hence fast heat release.

2. Retain Heat (Insulation) - All things compost faster as a function of temperature (read about the Q10 equation here). No compost heap will compost faster unless it retains heat. Plastics are very poor heat insulators - do not get fooled by names like 'thermo' and a few extra mm of plastic. You need a top quality, waterproof insulated material/ Just like your loft insulation ask for U or R value rating! Most tumblers have no insulation of any significance so they do not retain heat. The HOTBIN is designed to control both conductive heat loss (via insulated walls) and convective heat loss (hot air flow). If your goal is to hot compost; walk away from non-insulated bins. If you goal is to compost typical amounts (2-5Kgs) of food waste through winter, check the insulation works - look for user endorsements offering time & temperature graphs using on known amounts of waste (Kgs/week). We are NOT aware of any insulated tumbler guaranteeing winter hot composting of 2-5Kgs per week.

3. Aerate The Waste - You can hot compost without turning! The science (ref in T Huag, Compost Engineering) states air introduced via turning will last only a short time. If you have twiggy/woody material that maintains ‘free air space’ structure and a temperature gradient, it will aerate via buoyancy air flow. Take into account - spinning or turning a compost tumbler is not always easy. 100 litres = 50 Kgs, 200 = 100kgs. Even with levers this can be hard and it places huge stresses on plastic and metal joints.

4. Control Moisture - The moisture level in a composter is critical to the composting process. Kitchen scraps are wet, as are grass clippings - these need to be balanced with dry materials. Some tumbler models have drain holes in the drum, and also a collection chamber in the base to receive the "compost tea". Wet waste - wet waste tends to rise and then slumps to bottom - it churns into a solid sludge - the last thing you need! Wet waste is the norm when composting all food waste. This is really easy to handle in the HOTBIN - you just add shredded paper and bulking agent to balance the system. Leachate: most of the excess water is driven off as steam in hot composting. Some excess will drain down. Look for a bin/tumbler that has some form of leachate collection.

5. Control Odour - All composting produces odour. Aerobic composting avoids anaerobe pungent putrid odour - but it has a cabbage odour. You need to filter odour and reduce the any possible chance of attracting flies and vermin. Check if your tumbler has any odour filter mechanism - the HOTBIN does!

6. Pest Control - Do not get sucked in by statements like "compost tumblers are 100% pest proof since they are fully sealed".  We believe no domestic compost bin is rat proof. Rat experts will tell you they will eat through all plastics (be it 3, 15mm PE or 50 mm EPP as in the HOTBIN) if there is any gap. Understand vermin - what attracts them (odour, warm and quite nesting sites), then look for design that makes the bin highly rat resistant.  If you bins has ANY open holes of 0.5cm or larger and odour you will have problems sooner or later. Always look for off the ground, and look for a filter that removes residual odour to a very low non-nuisance level.

Group 2- Usability Factors

What are the key items that make it easy to use:
  • Assembly
  • Loading and unloading
  • Control

Assembly: Bit of a preference - we suggest you look for bins that come ready assembled or at least require very little self assembly. HOTBIN requires none. Loading and unloading: small loading and unloading hatches panels are fiddle and difficult to use - it is a big issue for some composter. Some tumblers are good - others are hopeless. The HOTBIN is OK.

Batch or Continuous: You can fill the HOTBIN to the top and leave a batch to mature (batch) or more commonly, you keep filling at the top and take out the compost from the bottom without stopping (continuous). With most tumblers there is the issue of when to stop adding new materials so that the whole composter can "finish" and the compost can be removed. Dual chambers are better than single so you can swap compartments, otherwise you may be looking at two bins. (This is a bigger issue if your goal is compost food waste over winter as you cannot stop for 2 months.

Durability: Choose carefully! Tumblers tend to be more heavily constructed since they need to be strong enough to hold the full weight of the composting materials. This does not always work - many fail at the joints and stands. Inspect the supporting legs and the central axis connection - they should be built to last years of use (Check for customer’s reviews after years of use!).  The HOTBIN has no moving parts - and only a door to take on and off.

Capacity: Avoid thinking bigger is better.  Hot composting is typically 10-30 times faster - so you need vastly less capacity. When hot composting, match the size to the amount of waste - it is harder to get a big tumbler hot with a small amount of waste - the laws of physics do not support small amounts of waste getting or staying hot in large empty bins!