1. Background

Beginning of December and it is getting cold out there. Even wearing the thickest woolen sweater one starts to freeze and with increasing energy prices, switching on the heat becomes more unattractive every year. In fact, the German federal agency for consumer protection estimated that the average German family had to pay some € 5100 for gasoline, electricity and heating in 2013, which is a 34 % increase compared to what they payed in 2008c The average annual costs to heat a 70 squaremeter appartment in 2013 ranged between € 970 and € 10501. Compared with the amount that had to be paid for the same appartment in 2011 the costs for the different heat supplying sources increased, ranging from +7,7 % for gas, +11,2 % for oil and + 9,6 % for distance heating. As can be seen, the price for heating energy depends on the supplysource. For example households heating with oil spend some 20 % more than those heating with gas2. With the steady depletion of fossil fuels such as oil, gas and coal, the prices for energy will further increase every year.

This does not only pressure the wallets of houseowners and tenants but can actually result in health impacts for the residents. Especially in England the term fuel poverty is well known and reappears annualy in the news. People who are simply not able to pay their energy bills get disconnected from the supplysources, a situation that foremost in winter has severe impacts on their health3.

However there are other components that influence the amount a household has to pay for heating energy. Most importantly, the characteristics of the present insulation of a building. The more heat it can keep within the rooms, or store in the walls to give backt to the livingspace, the lower is the energy bill. With a proper understanding of materials and investments into insulation the annually increasing costs for energy can be counterweighted and the one or other penny may even be saved.

2. Opportunity

Part of saving energy and costs is to understand the materials that are used for the insulation. The most important characteristics it has to fulfill are to shield the warm indoors from the cold outdoors (or in summer the other way round), store heat inside the walls and allow breathability to avoid a build up of mold. Clay is one of the oldest building materials known and combines these characteristics flawlessly. In addition it is cheap, abundant and an all natural product. It can be either burned to bricks or used as plaster. As opposed to concrete bricks, those made from clay have a lower heat transfer and thus a better storage capacity4. Furthermore, houses build from clay bricks are more durable and provide a more natural room climate5. Traditional plasters made from a mixture of fibrous materials and clay combine thermal benefits with breathability and are thus an efficient and cheap alternative to those made from concrete.

For the construction of new buildings it may be worthwhile to consider clay as a building material and benefit especially from its heat storing characteristics.

To see the great heat storage efficiency of clay we want to introduce the Pot Heater, which is this week’s do-it-yourself project.

3. Do it yourself – Potheater

There are some general advantages of the Potheater, such as saving energy and fuel and thus the one or other penny. Moreover it is an effective way to heat off grid as the clay pot can actually store alot of heat for a long time, while only requiring a small energy source. Combined with the simplicity and size of the pot heater this makes it a great alternative as an off grid source for heat. In general the pot heater may be nice to have in any outdoor gathering when temberatures drop: whether on a camping trip, in winter on the front porch or in your garden shack.

Besides the aspect of heating you can also test whether the pot heater can be used for cooking purposes in a similar way to the tradtitional Arabic Tajine or the Roman clay baker.

This project combines the practical work with natural materials with explaining basic physical principles of fire, heat storage and airflow, making it a great aktivity especially for school children.

Here is a basic list of the materials you will need:

3 x Terracotta flower pots (non-glazed), different sizes (!)

1 x Threadded rod or screw ca. 15 cm long, and 2 cm diameter (depeding on the pot)

6 x Nut that fits on the rod

6 x Steel washer different sizes

3 x Tea lights or small candles

Now assemble the pots as shown in the graphic below. The nuts and washers are used as placeholders and to fix the pots to the rod. Stack the pots into each other and make sure that there is 2-3cm space inbetween them. Furthermore, the inner pots should not extend beyod the rim of the outer pots. Now, find something heat resistant and stable to put the construction on, place a candle underneath the centre of the smallest pot and wait for it to keep you warm.

For more information you can find video instructions on youtube 

There are detailed construction guidelines available online:


potheater Potheater We Blue








Combustion-Free Hot Water at the Whole Systems Research Farm

Making Soil and Hot Water at the Same Time:
Testing the first generation of Jean Pain woody-compost water-heating mound at Whole Systems Design’s Vermont hill farm. We are now 2 months into testing our first mound and the results are astounding with hot water able to be harvested from the mound at a rate of about 1 gallon/minute at 120 F continuously, or cycles of 145F water harvested in 30 gallon amounts. We will be using this mound to make soil for the gardens and fruiting perennials on the farm and for in-soil bed heating of our greenhouse for season extension. Details on how to make these and other resiliency systems are in our workshops and in forthcoming videos released on our website,, these video channels, and announced on the Whole Systems Design and Bright Blue Facebook pages:….