Home-made low-cost stove night storage heater from strawcrete and stone

For some time we have been toying with the idea of changing the heating system in our sitting room and even considered starting over from scratch and making a rocket mass heater. However, we actually have a fully functioning and useful Godin in there, which it would be a shame to part with. To this end we have decided that it would be quicker and more economical to actually work with what we already have and build what is known as a 'night storage heater'. thermal wall or heat sink at the back of our stove.

Introduction

Our house is heated  entirely by wood-fired appliances: in our kitchen we have a clean-burn wood-burning cooker which by convection heats the rooms above.

The walls, as you can see we insulated, in the kitchen with chopped straw and lime and then on top a layer of hemp and lime. Paradoxically, if we had left the space behind the cooker and the Godin bare we would have had a natural heat sink ready made. However, this is a 300 year old vernacular farm house and the bare walls, unlike the section over the fireplace were not particularly decorative and were never meant to be exposed to view. In the past they would have been whitewashed with lime, probably on a yearly basis.

The cooker is set partly into a huge granite fireplace which itself acts as a heat sink, thus providing the room with some heat even when the cooker isn’t lit. Thus, I have been thinking how I could create something similar in the sitting room.

In our sitting room we have a small Godin stove, which we bought second hand some 16 years ago now and it is on this

that I need to focus my attention before the arrival of Winter. The stove works really well, even though it is primarily set to burn coal and even in the coldest periods will rapidly heat the room. The only real problem with it is the room gets too hot resulting in us letting it burn itself out and then having to relight it as the temperature drops.

What I want to do is store some of the heat emitted by the stove and to let it  transfer its stored heat as the room temperature falls – exactly as a night storage radiator works.

To this end I have decided to build a heat-retaining wall behind the stove. I am planning to make it very economically entirely of stone from the garden and using a lime mortar in the construction. I estimate the material cost to be somewhere in the region of between 5-10 Euros, which at the present rate of exchange is approximately  £4-8  or $6-13 US

Design

The stove stands on a tiled plinth, the plinth is laid on a  foundation on the ground beneath the suspended wooden floor.

To avoid removing the tiles I chose to build the wall on a strawcrete pad , this to furnish a ‘softer’ interface between the tiles and the walls and to ensure minimum heat loss from the wall by conduction into the plinth.

I had initially thought of building the wall in an adjoining stable and transporting it, still in its’ shuttering, into the lounge. I rejected this idea when I realised that the completed wall would weigh in the region of 180-200 kg.

The 'soft' lime mortar to be used between the stones will withstand the elevated temperatures.

Materials

Strawcrete: made from chopped straw mixed with a lime mortar. I had used strawcrete before as an insulation material on the interior walls of our kitchen. One of our outbuildings had a loft full of straw, this I chopped using a modified lawnmower. The strawcrete made from this material made a significant difference to the warmth of the kitchen and the following summer we plastered the entire kitchen walls with hempcrete on top of the straw.

We now buy the straw from a local organic dairy farmer to use in our hen houses. The long stalks were unsuitable for the strawcrete and needed to be chopped into shorter lengths. Some time ago I made a guillotine from some steel scrap to chop up old fruit crates for kindling. I found this could chop the straw after I had ground the blade to a more acute angle

You can find the film on how I made this guillotine from scrap metal here

Stone: The stones used are those which have already been used in the walls of the house and have been removed in the construction of doorways and windows.

Lime: I use hydrated lime NHL 3.5 

Safety gear: Although hydrated lime is much less aggressive than aerated, it will sting if you get it on your skin or worse still, in your eyes. You should therefore provide yourself with a pair of thick rubber gloves and a pair of eye goggles. It is also a good idea to keep a bottle of clean water on hand just in case of any slip ups, so as to wash off any splashes of lime.

Quantities

When working with natural building materials one of the first things you notice is that they are not uniform. This was something we were very much aware of when insulating our house walls and floors with linen, hemp and straw, on no day were either the mix quantities nor the elasticity of the mortars the same. They were dependent on humidity levels in the air, ambient temperatures out and inside and the different batches of the raw materials. There is obviously certain quantities one can work to but be aware that you need to get a feel for these materials as you go along and that, in particular the quantities of water used will not always be the same. However, take your time, work slowly and enjoy being in tune with the organic qualities of natural building.

We found in general when we worked on our house that the quantities of linen, hemp and straw to water and lime were pretty much the same. They were as follows:

1 bucket of lime (in a 35kg bag or 77 lbs of lime, there are just over 5½ buckets)
1 kilo (2.2 lbs) of straw, hemp or linen
6 litres (8¾ Imperial pints) (1.32 Gallons US) of water

Construction

The first stage was to make the strawcrete pad.

I constructed a wooden mould to the required size and lined it with a thin polythene sheet.

Next I mixed a mortar of lime and water.

I kept slowly adding water to the lime until the mix had the consistency of a batter, you will see this more clearly in the film.

Once this was mixed to a smooth consistency, I added the chopped straw.

As with the water, I added the straw little by little, mixing it into the liquid with each addition.

I was seeking the stage where there was no longer any liquid lime left in the mixing receptacle and all the pieces of  straw were coated with the lime mortar.



The mix could then be transferred into the mould, ensuring that strawcrete was tamped into the corners and along the bottom edges of the mould.

In between the addition of strawcrete the mix in the mould was tamped down using a wooden block.

Once full the excess strawcrete was scraped off using a straight piece of wood and the pad was left to dry.

Thus stage one of the storage heater is completed, the rest will be built in situ, follow this link for: Part 2 Building the Wall Now if you'd like to, sit back and watch the film.

If you have enjoyed this post and found it useful, feel free to share it, comment, ask questions or relate your own experience of using strawcrete. Hope to see you for part two and in the meantime all the best from Normandie,
Andy

© Andy Colley 2014

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Make a Wooden Fuelless Cooker or Hay-box - No Power? No Worries. Hot Food.

The cardboard box version of the fuelless cooker as described in my post a few days ago is fine as a 'quick fix' or an emergency back-up. In this post I'll share how to make a more robust model which you can keep to hand in the kitchen or, as we show in the film, to take in a car to provide hot, nourishing food on a journey. There are two ways you can use a fuelless cooker, firstly you can use it to cook a whole meal, this was the way it was used in previous centuries both for men and women working in the fields and long distance travellers and how we used it in the film. Secondly you can use it in your kitchen, to save energy when cooking a stew or similar dish, which requires slow cooking. We actually did this too with our cassoulet when we returned home in the evening, taking it from the box, where it was still quite warm and transferring it to our wood cooker. I have to tell you that after several years of making and eating this dish it was the best we had ever eaten! Furthermore we had saved on four hours of fuel.

Design and Materials

Our wooden box sits next to the telephone and is robust enough to act as a comfortable low seat. It was made using pallet wood and 10mm (3/8") thick pine cladding. This latter was left over from when I made the hen house last year. The insulation was 45mm (1¾") thick organic hemp and vegetable fibre, purchased in a 1250mm x 600mm (4' x 2') sheet for about $5.00.

I based the design of the box around our largest saucepan and for ease of loading when hot, the lower portion of the box was not much higher than the two handles on the side of the pan (as seen above). The box lid was deep enough to fit over the portion of the pan standing above the box rim.

Both the base and the lid were made in the same way, that is the vertical sections that made up the inner and outer walls were stapled to an upper and lower square frame, the width of the frame was the thickness of the insulation. 

I arrived at the box dimensions from the size of the saucepan. This size would be the minimum internal dimension of the box. To arrive at the outside wall height for the box base I had to add the thickness of the box bottom, the insulation and the thickness of the platform wood. I always tend to regularly check the measurements especially prior to cutting the wall material - better to be safe than sorry!

I had originally thought of making the frames like picture frames, with mitred corners but decided against it for two reasons, one is I'm pretty crap at achieving consistently accurate cuts, especially at 45° and secondly and more importantly I didn't believe that sort of joint would be strong enough to cope with the load from a pan full of hot stew! 

Construction

 


Select the pallet wood for the frames, cut to width (that of the insulation thickness) plane it smooth and cut to length.

Four frames are needed (2 for the base and 2 for the lid). To ensure they are all exactly the same size assembled them in a jig. I made this by screwing three straight pieces of wood in a 'U' shape to a piece of chipboard. The size of the U being the size of the frame and the corners at right angles. 
    

Position the two vertical legs of the 'U' against the sides of the jig and check that they touch the bottom jig edge, apply wood glue (PVA) at the corners and put the third, horizontal part of the 'U' along the corresponding jig edge. Ensure that all 3 pieces are pushed firmly against their guides and staple or nail where they overlap. Turn the, now joined three wood pieces around in the jig so that the fourth, open side of the 'U' is sitting against the bottom jig edge. Once again glue the corners and position the fourth piece of the frame on top and staple or nail.
 
The reason I used a 'U' shaped jig and not a complete square is that it is much easier to remove the frame by sliding it out rather than trying to lift it.
Repeat for the other three frames and then stack all four frames and clamp at each corner and leave to dry.

The bottom face of the box has pallet wood planks nailed to the frame to form a solid support.

Turn the base over and cut and fit two extra pieces of wood to the frame. This is to furnish a vertical face to which the box walls can be attached.

The saucepan is to sit on an insulated platform made to fit into the square recess created in the previous stage. The platform is about 20mm smaller than this recess to account for the wall thickness and is deep enough to fit a square of the 45mm thick insulation beneath it. Being removable it can be taken out and cleaned if there is any spillage.

 

Now comes the clever bit, I already know the height I need for the box base so I measure the internal wall height and include the height of the insulated base. Cut the 10mm cladding to this length.

Use panel pins to attach the walls to the base. Ensure a good fit at the corners.

The base now looks like this. 

Prior to fitting the top frame to the base, attach two additional wooden pieces, so as to make a flat surface to the frames upper face.

Nail, or staple the top frame to the walls of the base.

The box now looks like this. The outside walls can be cut to length and the insulation cut to size for the walls and the insulated platform.

 

The insulation should be a good, close fit to ensure maximum efficiency.

Attach the outer cladding. I tend to use the stapler because it's less tedious but panel pins are fine.

Cut two carrying handles and fix to the box, screwed through the walls into the upper frame.

The insulated platform can then be dropped into the completed base.

The construction of the lid is similar to that of the base except that the top outer cover of the lid is put on last. I found that this makes it easier to attach the inside walls to the frames.

 

First, cut the interior walls to length, which is the height of the pan  and lid projecting above the box base plus the insulation thickness and the thickness of the cladding covering the insulation.

Fix the interior walls to the lower frame........

............and the upper.

To make the space for the insulation at the top of the lid cut two 45mm wide pieces of wood to the internal dimension of the lid and wedge them in place at the top of the lid, with a few millimetres protruding above the uppermost face.

Cut cladding to fit to these two pieces and attach. The cladding must not overlap the edges.

Remove this assembly, turn it over and put it back into the lid top.

 

Tap it flush to the upper face of the frame..........

..........and attach to frame.

Cut insulation for walls and

top, cut cladding and attach.

Cut and attach two handles, securing them, as before, by screwing them to the upper frame.

 

To ensure a snug fit of lid to base, cut four pieces of fruit crate wood (5mm pine), to fit around the inside of the lid perimeter and chamfer one edge of each piece.

Staple, or nail these pieces to the inside wall of the lid, chamfer facing out and protruding about 10mm. This acts as a guide to align the lid to the base and produces a more effective seal to prevent heat escaping.

And there it is all ready for the next power outage, energy price hike or picnic.

Bon appétit! Now if you'd like to sit back and watch the film: 

If you would like a cheap and cheerful project, which is great fun to make and use, then take a look at my cardboard box fuelless cooker design


Thanks for dropping by and please feel free to share this article, comment, ask questions and if you'd like to be assured of getting the next post, then sign up to follow this blog.

All the best, Andy

© Andy Colley 2014

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How to Make a Simple Fuelless Cooker or Hay-box - No Power? No Worries. Hot Food.

Here's a quick and easy way to use less fuel, less water and still have a tasty and nutritious meal from a cardboard box. Get one ready in case of power outages or for hot food on a journey or emergency.

The Hay-box or fuelless cooker was a popular item around the turn of the 19th to 20th century. In particular during the World Wars and the Great Depression when people were often displaced and the price of fuel rose steeply and/or was rationed. Furthermore, it provided a form of cookery which used less water and in which, precious food, cooked at an even temperature by residual heat had no chance of burning and becoming spoiled. There was also the added and important factor that nutrients were retained through the slower and lower cooking times and temperature.
 

 

We cook all our meals and heat water with our wood-burning cooker. In the colder weather it is alight most of the day heating the house as well. As we move into the milder weather we tend to eat more raw food and as we have no need of the heating so the cooker is alight just around meal times. This poses a problem in that we do need hot water for washing hands when we come in from the garden prior to preparing our food .

 

We solved this problem by using a Hay Box to keep the water, heated at meal-times, hot. We made our first box from scrap wood and filled it with organic lucerne hay which we are given by the organic dairy farmer from whom we buy our chicken grain.

The idea is not a new one, in our 1920’s copy of Mrs Beeton's Book of Household Management the Fuelless cooker was used to cook meals for a fraction of the fuel cost. Nowadays it is just as important to consider the fuel-saving benefits of such a system as well as bearing in mind the possibility of providing hot food during power outages in the colder weather.
 

The principle is that the heated food is placed, in its pot or saucepan, into a well-insulated box , the lid which is also insulated is put in place and that’s it! The food takes about 4 times longer to cook completely within the box and may need to be reheated prior to serving but the only  energy consumed has been that needed to get it to boiling point. Of course, the ‘box’ part of the system is only required for safety and neatness and possibly transporting, I know of others that have simply wrapped duvets around the heated pan and achieved the same end result and have a warm duvet to boot!

 
 
ORGANIC LUCERNE HAY

ORGANIC TRITICALE STRAW

ORGANIC VEGETABLE FIBRES

ORGANIC HEMP AND LINEN

HOLZFLEX WOOD FIBRE

ORGANIC SHEEP'S WOOL


I used an ecological, non-toxic insulation for my box and there are a multitude of suitable insulation you can use: fleece material, multiple layers of corrugated cardboard, hay, straw even expanded polystyrene, the choice is yours. 

The first box I’ll share is the simplest and cheapest. We are very fortunate in having a local ecological building supplies company (in fact it’s next door to our organic supermarket) and I could buy single panels of  wood wool insulation 30mm thick for around $3,00. On  the same visit to buy the insulation we popped into the organic shop and picked up two cardboard boxes of similar proportions but different sizes. 

The insulation needs to be cut to line the four sides and base of the larger box and the smaller box should fit in the cavity that remains. I was able to find cartons whose sizes differed by about 60mm hence the 30mm insulation on the inside walls of the larger carton would be sufficient to form the space for the smaller carton.

 

To make the lid to the Hay Box I cut two rectangles of cardboard to the size of the larger carton and made a ‘sandwich’ with the insulation between them. The lid was held together with broad masking tape. I adhered the tape around the perimeter of the lid so as to seal in the insulation.

And that’s it, the box is ready to go. When the saucepan is put into the box, the voids at the box corners can be filled with triangular-shaped pieces of cardboard (a bit like ‘Toblerone’ boxes) or stuffed with tea towels, ideally any kind of insulating material which will reduce heat loss due to convection currents.


Next time I’ll share  my design for a wooden hay box, more robust than the cardboard one it is more suitable for carrying hot contents in a car so you can enjoy your own hot food on a journey.

Meanwhile, if you'd like to, sit back and enjoy the film:

Thanks for dropping by and please feel free to share this article, comment, ask questions and if you'd like to be assured of getting the next post, then sign up to follow this blog.

All the best, Andy

© Andy Colley 2014

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