HotBin Mk2 Composter Review

I first heard of the HotBin several years ago, when I was discussing gardening with the owner of the local convenience store. Chris is a keen gardener, and in-season grows nearly all the veg he sells his village shop.

It was spring, and the conversation soon turned to getting the garden ready. Chris told me he didn’t dig his garden, he just added a layer of compost to the surface.

“How do you get enough compost to do that?” I asked.

“We have two HotBins – we have more than enough compost,” Chris replied.

I’ve been intrigued ever since then, but it was only in 2019 when I was given one, a HotBin Mark 2 compost Bin, as an early Christmas present, that I got to play it.

I’ve been using the Hot Bin for a month at the time of writing. This product is well known, and won Chelsea Garden Product of the Year. Does it live up to the hype? It’s time to find out…

I’ll be using the inverted pyramid method for this review first- covering the most important information first, with additional details for those who want to know more further down.

How did I review this?

To put this review together, I conducted a one month trial. I also conducted research on the HotBin before and after receiving the product, and went through dozens of customer reviews. HotBin did not provide the product to me, and my opinions are my own. I’ll continue testing the Hot Bin and updating this review over the next few months.

At a glance: What does it do?

Getting fast, effective compost can be difficult with limited materials, especially with an open pile. The hot bin aims to make it easy to produce good compost quickly, whatever time of year it is, and bring hot composting into the reach of people who don’t have the volume to create a large pile.

How good is the HotBin?

After a one month trial, I found it exceedingly easy to achieve hot compost, regularly getting temperatures over 60 degrees celsius during the middle of winter.

HotBin claim to make rough compost in one month, and fine compost in three months – after one month I found that while the compost had made good progress, it was indeed very rough (see pic at the bottom of this post.)

Hotbin Pros and Cons

Pros

  • Rapidly reaches effective heat levels
  • Makes hot composting feasible even with smaller quantities
  • Tough construction
  • Composts well in cold weather
  • Easy to use

Cons

  • Important to follow instructions to get hot compost
  • Need to add bulking material to achieve best results
  • Can’t handle huge amounts of garden waste
  • Compost in one month claim may be a bit ambitious

Delivery

Delivery was promised at 10 days, but the HotBin arrived in 4 days (which included a weekend). Delivery was also under-promised and over-delivered for an additional order of bulking material.

What’s in the box?

Hot Bin Contents.

In addition to the HotBin, you also get the following:

Two straps: These are designed to go around the base of the HotBin Mk2, securing the opening. However, the straps are large enough that they can also secure the HotBin to another object. I used one for exactly this purpose, securing one to a pallet compost bin to ensure the whole structure was stable.

Thermometer: This is designed to measure the temperature of the actual compost. It’s proved useful, as the external thermometer usually shows a higher temperature than the internal temperature. It’s also great fun, and allows you to see directly very quickly how different ingredients affect the temperature of the compost bin.

Hot water bottle (ok, officially known as kick starter bottle): My nieces were tickled pink by the fact I had a hot water bottle for my compost bin! I used this at the start, but after the first two days didn’t need to use it again.

Stirrer: Designed to stir the top contents of the bin – highly useful when adding compost ingredients, paper and bulking material together.

Instruction booklet: Fun and easy to read. I did as instructed, which was grab a cup of tea and sit down to read it!

Bulking Agent: You also get a 20 litre of bulking agent for mixing in with compost ingredients.

Leachate cap: The small blue cap featured is designed to go over the drain at the base of the HotBin. When opened, this allows you to capture the leachate which can be used as compost tea.

How good was the customer service?

To check customer service, I sent an email to the HotBin customer service asking what the cap was for. The email was sent in the evening, and they replied at 1.05pm the next day, four hours into the working day. The reply answered my question clearly with a tip on how to use the cap correctly, contained a photograph to illustrate the answer and contained additional information from the HotBin website.

How well does it work?

HotBin Thermometer.
At times the HotBin reached temperatures well above 60 celsius.

The Hot Bin is a very effective composting system. The well-insulated material and flow of oxygen means that you can achieve rapid heat and compost with smaller amounts of material that would be impossible with other composting systems, without having to turn the material. The Berkely method of composting is faster, but this requires building a large compost pile in a short period, and turning it regularly – most people simply don’t have the material to do this.

It’s worth noting that while the design is excellent, a lot of the success relies on educating the compost maker. The addition of shredded or torn paper, along with bulking agent (HotBin recommends partially composted wood chips) is essential to successful composting with this system. Failure to add these (or similar elements) is likely to lead to a sludgy, wet result. To maintain hot composting, the HotBin also needs regular feeding – leave it for a few days and it will rapidly decrease in heat.

The biggest downside is the addition of semi-composted wood-chips. These can be expensive if bought from HotBin, and if you are using the HotBin to full capacity you might want to make your own over the longer term. Alternatively, you can use regular wood-chips and accept it will take longer to make finished compost, or make your own bulking material.

HotBin or HotBin Mini?

There’s two types of Hot Bin, the regular version and the Hot Bin Mini. The Hot Bin Mini comes with a capacity of 100 litres and the Hot Bin comes with a capacity of 200 litres.

Although it was winter and I had limited materials, I had no problem filling up the 200 litre Hot Bin. I used a mixture of home waste, some waste collected from the office, withered leaves from my brassicas, chicken bedding and some kitchen waste. Before my one month trial was up, I found myself rationing how much compost material was going in.

If you have a garden and a family of more than two, you are probably better going for the larger HotBin, which after all gets you double the capacity for an extra £50.00 in the UK. (At the time of writing, only the larger version seems available in the US.) If you have a small garden and family, the HotBin Mini might be a better option.

Construction

This is one tough bin, as I found out completely by accident. My bin was delivered shortly before a major storm, and even though I put it in a side-passage for protection, the wind lifted the whole thing up and threw it across the garden.

Twice.

So I was nervous when I unwrapped the hot bin, but I was relieved to see there wasn’t any damage. The bin is super light, so to avoid future damage I have attached it to one of my pallet compost bins with a sturdy rope.

How does it work?

The Hot Bin utilises basic composting science to ensure efficient composting. One of the keys to fast composting is ensuring sufficient heat for composting bacteria to function in, and the Hot Bin utilises highly efficient expanded polypropylene to retain heat for longer.

A second function is oxygen, and one reason so many composting systems require regular turning is to provide sufficient oxygen for the bacteria to continue producing. The Hot Bin system is designed to ensure airflow through the bottom of the bin, but you achieve this by placing a layer of twigs at the bottom and by adding semi-composted wood-chips, which HotBin call a Bulking agent, into the mix. This creates Free Airspaces in the compost, removing the need for turning.

Another key with the system is to add shredded paper – the instructions advise adding shredded paper or torn cardboard equivalent to 50% of the compost material you are adding, in addition to bulking chips equivalent to a 5th of the compost ingredients. From a practical point of view, the additional carbon rich material probably helps to ensure the nitrogen level in the compost is not too high, as well as helping with the structure of the compost.

Bulking Material

One downside of the system is the need to buy Bulking agent. This costs £24.00 in the UK for a 50 litre bag, or £39.00 for a 100 litre bag. HotBin recommend adding a fifth of the material you use for compost, so if you are adding 15 litres of material a week, you would be adding 3 litres of bulking agent at a cost of about £4.00 a week.

An alternative is to use your own wood-chips. I enquired at a local woodyard and found I could buy a ton of wood-chips for £40.00, although with a woodyard you might not be able to guarantee they are organic. Fresh wood-chips are likely to take longer to compost than semi-composted wood-chips, but if you are patient you should be able to leave them to semi-decompose. HotBin advise using dry woodchips, so these should be covered with a tarpaulin in wet weather if outside.

Of course a ton is a lot of wood chips for a single compost bin, but after seeing the success of the Hot Bin I am very keen to experiment with wood chips with other composting systems.

Commitment required

Ideally, the hot bin should be ‘fed’ every couple of days. Unfortunately, when I trialled the hot bin commitments took me away from home twice, so I wasn’t able to stick to this to the letter. Fortunately, I found that while it cooled down if left for a few days, adding more material rapidly increased the heat again.

For best results it’s best to chop up larger material. The weather was far too wet to mow materials in my garden, but I found that spending a minute or two chopping up material with a pair of shears was sufficient to get the bin hot.

Hot Bin Testing

Hot bin contents.
Hot bin contents with shredded paper to soak up excess liquid.

For the first round with the Hot Bin, I wanted to do things as close to the rules as possible. Unfortunately, as I needed to be away from home for several days (twice) I wasn’t always able to give it quite the attention it needed – but this didn’t seem to matter.

As it was winter, and I didn’t have the usual surplus of materials from my garden, I had collected a large sack of waste. This included some garden waste (mostly brassica leaves which had withered), some chicken bedding and kitchen waste. A negative is that the decomposition process had already started with this material, but this didn’t turn out to be a problem.

I roughly chopped the material with a pair of shears, added the material to the compost bin with compost wood chips and shredded paper and added the hot water bottle that came with the hot bin (after filling it with hot water first, of course!)

Kick starter bottle.

The kick starter bottle increased the temperature by a few degrees, but by the second day the temperature had sunk down to the previous level. I then added kitchen material I had collected from the office with more paper and wood-chips, and replaced the hot water bottle.

On the third day the temperature had increased, reaching an internal temperature of 50. I continued to add material until the temperature reached 60. I carried on adding material at a regular basis, although not, as suggested, every other day, due to commitments taking me away from home.

At one point the temperature got rather high. I’d added chicken bedding heavy in manure, bringing the material near to the top of the bin, and the internal temperature reached 68 degrees. Some (but not all) sources believe that temperatures above 65 celsius can kill beneficial bacteria if it proceeds too long, and I had to add a lot of “browns” in the form of shredded paper, cardboard and even some finished compost in order to bring the temperature down again. (While I’ve taken pictures of some of the temperature readings, when it was above 65 degrees the internals were too steamy to photograph.)

After two weeks of hot composting, I opened up the door at the front. At the bottom the contents were starting to mirror compost, while a web of white tendrils showed that Actinomycetes were permeating the compost, and starting to digest the harder materials. I opened it up again a few days later and found a number of white mushrooms growing. (They looked very tasty, but I didn’t try eating them!)

Mushrooms in the hot bin.

At this stage the temperature measured 20 degrees celsius at the very bottom and 30 degrees further up.

Towards the end of the test I was away for six days and could not add any fresh material. The day after I came back the temperature had dropped to around 40 degrees, and continued to drop further. After adding some more kitchen material, mixed with paper and urine, it increased to 50 degrees. A couple of days later I added in some chopped up chicken bedding, and at the the temperature increased to 61 degrees celsius.

After one month, I found the temperature at the very bottom was 15 degrees centigrade, which compared with 3 degrees in my maturing compost pile. Digging a section out at the bottom, the material was well decomposed, but some way off being fine, finished compost. I did pop it in a bucket and take a photograph, so you can see what the results are after like one month.

I’ve now left the compost to mature to see how well it performs after a longer maturation process.