Drying your wood in a
solar wood kiln can be a great way to create your
own lumber, and they are actually more efficient than a standard wood
drying kiln or drying your lumber out in the open air. It is very rare
to find air dried lumber with a moisture content below twenty percent
which can lead to your lumber warping and cracking before you are able
to use it. A solar drying kiln can allow you to create lumber with a
moisture content between
six and ten percent which is almost unheard of.
Designing and Building
Your Own Solar Wood Drying Kiln
Below you will also find
how to calculate the most important aspects of your kiln. The ideas
are merely meant as a starting point for building your own solar drying
kiln. You can take these ideas and customize them to fit any size kiln.
We will simply touch upon the basics that must be included for a solar
kiln to function properly.
The most important aspect
of your DIY kiln will be the roof and the
solar collector. The roof needs to be at the correct angle to allow as
much sunlight into your kiln as possible. To determine the pitch of
your roof, you first need to know your latitude as this will affect the
angle of the sun. If you live in the middle of the US, the average
angle should be between 30 and 40 degrees.
However, if you are
on using your kiln during the winter months then you will need to add
another ten degrees to the pitch of your roof. So if you latitude is 35
degrees, you will want to have a pith of 45 degrees if you want your
kiln to function during the winter.
The roof should be
constructed of a
material such as glass or plastic that will allow sunlight, and more
importantly heat, into your building. The roof should be very similar
to that of a solar greenhouse.
Another very important
thing is that the
pitch of your roof should face south to allow the most sunlight inside.
This means that the north wall of your structure should be much taller
than the south side so the pitch of the roof is facing the correct
The roof is essentially
your solar collector as it allows heat into the
building while preventing it from escaping. Your building needs to be
extremely well constructed and insulated to prevent heat from escaping.
The inside of the building should be painted with a sealant to make it
It is then recommended
that you paint the walls
and floor of your kiln with black paint. Painting the inside of the
kiln black will ensure that the heat that is allowed into your kiln
through the roof is then absorbed by the walls and contained inside the
A solar drying kiln may be
very similar to a solar greenhouse, except
there is one main fundamental difference. Humidity levels inside a
greenhouse are often extremely high, which is very beneficial to the
plants that are located inside the greenhouse. However, when you are
seeking to dry out lumber, humidity inside your box can start to become
quite an issue.
In fact, the reason that
solar drying kiln is better
than drying lumber outdoors is that the humidity levels in most places
is too high to sufficiently dry lumber thoroughly which is why the
lumber is moved into a drying kiln in the first place.
In order to
regulate the humidity level in your structure, it is necessary to have
a gauge which will read the humidity level inside your
will also want to have a remote read thermometer installed inside the
kiln so you can monitor the internal temperature of the kiln as well.
Different types of lumber require different drying times and different
Drying your lumber to quickly can cause the boards to
warp or crack, so you will need to be able to control your temperature. This can be accomplished
by adding vents at the top of the north wall.
These can be as simple as holes that you can cover with plywood when
necessary, or you may want to consider installing cheap solar powered
fans to circulate the heat more thoroughly through your kiln.
To determine the size of
your kiln, you will need to know how many
boards you want to dry at a time. A general rule of thumb is that you
need one square foot of collector (glazed roofing) for each ten feet of
1 inch thick board that you wish to dry.
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