Heating Using Compost? Why Not?

I bet you never thought about using compost to generate heat, did you? Mulch and compost are basically biomass and as it decomposes naturally, biomass creates heat as a byproduct. Why wouldn’t you make use of this heat?

If you’re new on Survivopedia, we already published a few articles about the numerous benefits of compost and mulch for your household. We talk about what mulch and compost is, how can you DIY, what can you use it for, what are the best kinds of materials to use and so on. Just follow the links to get the general idea.

Long story short, let’s to put the compost to work for us again!

The Magic Behind the Process

The idea behind using compost or mulch for heating is to capture as much of the generated heat as possible and use it for various purposes around the house such as reducing your electricity bill, heating bill etc.

Since any pile of compost, if big enough and healthy enough, produces a reasonable amount of heat during the decomposition process, you can use the respective heat for warming water. When I say healthy, I mean that it has a good ratio (1:1) of nitrogen and carbon.

Of course, you’ll save money on your energy bill by doing this and you’ll also reduce the amount of garbage that you send to landfills (again, saving money in the process).

It’s a win-win situation, regardless how you look at it.

Biodegradation is the process that makes the magic things happen in your compost pile and that means that the trillions of microorganisms living in your compost or mulch must be “happy” if you want to obtain the best results.

For a high rate of biodegradation (as in successful composting) you must achieve an optimum level of aeration, balance (in terms of nutrients) and moisture in your compost mound.

All these elements, working in harmony with the fungi and bacteria that “feast” on the waste matter which is part of the compost, end up turning it into humus, water and carbon dioxide. Humus is basically the “end product” of composting and heat is the highly beneficial byproduct of the process of biodegradation, i.e. the conversion of organic matter after it has been eaten by microorganisms.

It sounds a bit complicated, but actually it’s very straightforward after you begin to grasp the concept.

Now, if you want to use the heat that results from composting, you must know that a faster compost rate results in more heat generated during the process.

If you want to achieve the best results, i.e. the most heat, you’ll have to use big piles. The heaps must be at least 3 cubic feet or more while the perfect compost mound measures 4-5 feet in all directions. Only mounds this size or larger are able to generate temperatures over 140 degrees Fahrenheit.

The most heat is generated in the center of the compost mound; that’s the “hot spot”. The hottest temperatures obtained in such piles can be as high as 160 degrees Fahrenheit in “hot” setups.

This is a respectable figure if you’re taking into account that the USDE (the Department of Energy) recommends 120 degrees Fahrenheit as the ideal temperature for heating the water in your household.

Video first seen on The Curious Gardener

How Does It Work?

Now the question is how to use compost for heating your water and saving big on your energy bill, especially during winter season?

Well, the man who answered the question was a French guy named Jean Pain back in the seventies. Today’s projects are basically variations of this half-a-century-old idea.

The basic principle of compost-heated water is to use coils of plastic pipes driven through the compost piles, then pump water through them. The heat transfer occurs between the compost and the water and voila, you get hot water for free.

Jean Pain made some calculations and he claimed that a huge compost pile (50 metric tons of stuff) can be used to heat a small residence for half a year (basically in the cold season), at least theoretically. There are some important factors that must be taken into account, including the climate.

Generally speaking though, since water is an excellent conductor of heat, the compost-heating system requires only simple and cheap piping systems that are able to transfer the heat from the compost pile to water running through plastic pipes over the relatively short distances during the biodegradation process.

Hence, it’s no biggie DIYing yourself a heating system using compost for, let’s say, heating small spaces (barns, garages) in a closed loop system.

You can use fans for blowing air over the heated plastic pipes, hence acquiring a space heating system for a building such as your outdoor greenhouse. Another idea is to use the hot water heated from composting for your household, therefore saving big on your energy bill (hot water generally accounts for 14-25% of the costs associated with the cold season).

In Europe, people are actively using compost for heating their homes by building compost piles over coiled water lines made of plastic that use the heat from the biodegradation process.

The only moving part in this setup is the water pump. That makes this a very reliable heating system as you can imagine, requiring next to nothing to maintain. The compost pile is able to produce heat for a year and a half up to two years, providing enough heat during its lifetime cycle to warm 80% of the hot water required for a 1500 square feet residence. Impressive figures, don’t you think?

If you’re interested in using compost for your heating needs, you must learn the basics of creating a Pain Mound (the system invented by the aforementioned French guy). Usually a compost mound is made of sawdust and woodchips that are surrounded by a circle of hay bales which provides its structure and acts as an insulator.

A regular compost mound using the Pain system is typically 16 feet in diameter and 8 feet tall. You’ll require anywhere between 1300-3500 cubic feet of wood chips, an electrical pump, plastic piping for heat exchange and construction steel fencing. The steel is required for the plastic coil piping to stay in form, because heated plastic tends to deform easily.

If you’re living in a cold climate, you’ll require a bigger Pain Mound, but the beauty of the system is that you can reuse the materials (the pipes and the fencing system) for up to fifteen years in a row if you’re extra careful while you disassemble the mature compost pile.

There are quite a few design options for creating your own heating system using compost, but they all share the aforementioned common elements/gear/materials. This kind of project will take 2-3 days of labor and the most important thing by far is the correct setup of the compost mound itself, including the piping, coils and pump.

Your compost mound must be healthy, well balanced and aerated so the biodegradation process takes place continuously and efficiently, generating enough heat for your setup.

You could take a look on Instructables.com for a nice tutorial with pictures and all the necessary details depicting the how to’s of building your own heating system using compost.

Keep in mind that a pile of compost is prone to catching fire relatively easy, so watch out and avoid storing compost too close to your premises.

If you have any suggestions or comments, feel free to share your thoughts in the comment section below.

This article has been written by Chris Black for Survivopedia.

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