Mass Heater for a Greenhouse Using a Wood Stove
Architecture & Design: Mass Heater for a Greenhouse Using a Wood Stove
Kiko Denzer and I were hired to build a heater in a greenhouse for some
very avid gardeners. They had experimented with using a wood stove but
there simply wasn’t enough heat retained for the stove to heat the
greenhouse from one day to the next throughout the winter. Our task was
to incorporate the old wood stove, mostly taking advantage of the glass
door and firebox it offered, and plug it into a system with channels and
enough mass to absorb sufficient warmth to heat the greenhouse with one
firing a day. This article chronicles that build and the results.
Here you can see the long path that the smoke makes through the bench
after it has exited the original stove. Â All of the heat retained by
the bench would have otherwise gone straight up the chimney. Â There is a
bi-pass damper which acts as a valve and allows for a straight shot to
the chimney when you are making cold start.
Visiting in the Winter Time
The following photos were taken on December 3rd in the Willamette
Valley of Oregon. Â You can see tomato and pepper plants maturing inside
the greenhouse while the ground outside is covered in snow.
Step-by-Step Photos of the Construction Process
Dry
lay-out. Â I had carefully drawn out the heater and we had poured the
pad to planned dimensions… but it is always still important to check
that everything fits together as planned.
Kiko
instals wooden guides, often called “leads”, that will help us to keep
our corners plumb and allow us to run lines to level our courses. Â This
is more helpful on larger projects.
The
original wood stove that inspired the project. Â I used a 4 1/2″
grinder with a metal cutting disk to cut out the baffle shelf it had
inside.
We
laid up as many courses as we could behind the wood stove before moving
it into place because we knew we wouldn’t be able to get there to work
once it was there.
Now we have placed the wood stove which will act as our fire box. Â We are examining how the linteled course will go.
You
can see in this picture and the subsequent one that we have wrapped the
stove in 1″ ceramic wool blanket. Â This is both to ensure that the
metal stove has adequate room to expand and contract within its new
brick housing and also to raise temperatures in the firebox which will
contribute to a cleaner burn. Â In this photo, we are beginning to fully
enclose the stove with brick and beginning to define the down and
up-draft channels that will enter into and leave the bench.
Detail of the creamic wool and brick work surrounding the stove.
A cleanout is being installed at the bottom of the downdraft. Â We are using a soot door by Pisla and a masonry frame that surrounds it.
The down and up-draft channels getting further defined. Â Lintels to span the openings.
Before
the mortar has set up, we knock the lintels back and forth at least a
quarter inch to ensure that they will have room to expand and contract
when heated.
Project coming along. Â We have gotten above the height of the bench so….
We switch gears and focus on the bench. Â A rare shot of Kiko using cement mortar!
A The area the greenhouse is in experiences occasional flooding so we
built the first couple of feet with cement based mortar and made some
weep holes in the brick work.
We
chose to insulate the bottom of the bench channels (with a perlite-lime
mix) so that less of the heat would soak into the pad and ground below
it and more would go into the bench top.
Detail
of first flue liner plugging into brick work. Â We used ceramic wool to
help seal the union while giving the two different materials room to
move when heated.
The flue tiles are mortared to each other but very minimally mortared to the bench surround.
I’m
not sure why we hadn’t set up the brick saw. Â Cutting block with a
diamond blade on a skilsaw can be a dusty and noisy affair so put on
your safety gear.
The
next couple of photos show us marking a flue liner for an angle cut
using water in a wheel barrow to give us a mark all around the shape.
Each bringing the flue liner down to our marks.
Working
out the corners and also inserting the copper heat exchanger that Ed
had made to warm water up for watering starts and seedlings.
Flue liner assembly is completed. Â Cleanouts at end of bench to access both horizontal runs.
Framing up and reenforcing the concrete pad which will act as the bench top.
Mixing concrete, shoveling, and screeding.
Bench completed, back to brick work.
This
is an important photo which shows the basic design. Â You can see the
firebox and the bell that will be formed above it, and the down and
up-draft channels. Â The heater has been designed around the size of the
brick units to minimize cuts and complexity.
The bi-pass damper is put into place. Â When open, it gives the flue gases a direct shot up the chimney.
Another angle on the bi-pass damper and the shaft which leads to its operation on the front face.
You can see the lintel above the firebox as well as the bi-pass damper handle.
We
have used slabs made of castable refractory to cap off the “bell” above
the firebox and the entrance into the downdraft. Â An anchor plate with
a shut-off damper has been installed for the chimney to plug into.
A plaque made of left-over mortar to record the year in which it was built.
The
top of the heater is insulated with a perlite-lime mix in order reduce
the amount of heat accumulated at the top of the heater and encourage it
to absorb it into the rest of the heater.
The heater is near completion.