I wanted to show a few enhancements that I’ve
made to the pellet-fed rocket mass heater.
First, on the feed tube, I set up the feed
control gate so that it could be opened and
closed by turning a threaded rod.
This allowed to fine-tune the pellet feed
rate.
A couple of turns can make a difference between
a fair burn to burning extremely hot.
Next I added a gate part way up the feed tube.
Originally I was going to make it so the feed
control gate could close and let the fire
go out, but the pellets would continue to
gasify behind the gate.
Adding this further away would allow for the
pellets to burn out and leave enough space
between the fire and gate.
I added this flange to the bottom of the feed
barrel.
It allows for the feed tube to loosely connect
into the barrel and float around a bit.
This allows me to dump the pellets into the
barrel without worrying about moving the feed
tube.
Inside the feed barrel, I also installed a
sloped artificial bottom so the majority of
the pellets would go into the feed tube.
I also made a stand which supports the barrel
and top end of the feed tube.
It only takes a couple of minutes to convert
the heater from regular wood burning to a
pellet burning system.
Here’s the system burning wood again, but
I must say burning pellets is far less time
consuming and I’m finding they burn much
more consistently and hotter.
A little bit of stove paint really cleans
up the entire contraption and camouflages
my terrible welding job.
I also have a couple of other changes that
I made to the feed and burn areas.
First, I raised the feed tube a bit so the
pellets drop on to the grate when the feed
tube is out of pellets.
This helps to make sure all the pellets roll
out of the feed tube and reduces the risk
of the pellets burning inside the tube and
creating a backdraft.
Second, I redesigned the restrictor plate
so more air is forced over the pellets.
The plate can also slide back and forth so
I can adjust the amount of air that is entering
the system.
I find it’s best to close it up about half
way when starting, to help with the drafting.
Then open it all the way once the all the
pellets are burning.
You may recall while filling the foundation
hole for the dome, I installed 4” corrugated
pipe under the floor.
Finally you can see how this is being used!
Looking at the traditional heater, there is
the barrel which radiates out a lot of heat,
the exhaust running under the floor which
absorbs some of the heat, and the exhaust
to the outside where any remaining heat that
wasn’t absorbed elsewhere is vented.
While building the dome, I installed several
sections of corrugated pipe and they terminated
inside of a barrel that was open at floor
level.
Now it’s time to make some major additions
to the heater unit.
I’ve made a metal shroud that covers the
heater and barrel.
It has an opening at one side to let in cool
air, a baffle to force more air around the
barrel, and then a fan to blow the warm air
through the corrugated piping.
Next I installed two aluminum radiators.
One sits directly on top of the barrel and
the other above the blue barrel.
These radiators are tied to the existing circulation
pump for the aquaponics system and always
have water flowing through them.
I debated on coiling some stainless tubing
inside the barrel but didn’t for two reasons:
First the radiators were cheaper than the
tubing, and I can easily see the radiators
if they are leaking or need any maintenance.
Looking at the air flow through the system,
the fan draws the room temperature air through
the base opening around the barrel.
Some of the air is drawn over the baffle area
and some around the first radiator.
This radiator really gains most of its heat
from the hot surface of the barrel top.
Next all the air is drawn through the next
radiator, which draws a substantial amount
of the heat out of the air.
This allows me to just leave a cheap box fan
in the system without the risk of melting
it.
The cooler air is forced through the ground
where the remaining heat is absorbed under
the floor and exhausts back into the building.
The last odd feature I added was to enclose
the 8” exhaust pipe in a 10” section of
pipe and put in a blower fan.
This works well…especially when the heater
has been running a long time and the floor
temperature along the exhaust is basically
saturated.
Taking a look at the cover, it has a steel
frame and is then covered in sheet metal.
Each section can be easily screwed to the
other pieces so that I can dismantle it if
the rocket heater needs any maintenance.
This is the center baffle sliding into place
which is used to force the air around the
barrel and then down through the fan.
Here is a shot of the top radiator on the
barrel before I added the back cover.
And this is the front side of the heater where
the second radiator is mounted.
The box fan just sits on top of the blue barrel
that was buried in the floor.
The front cover quickly attaches so I can
access the radiator or fan.
The water lines for the radiators tap off
of the main pump line that circulates the
water through the aquaponic system.
It first goes through a screen filter to reduce
some of the solid buildup in the radiators,
which at some point I’m sure I will need
to flush.
Then there are two lines that run to each
radiator and the return lines then merge and
drain directly back into the fish tank.
Here are some of the temperatures for one
particular run.
A 40 pound bag of pellets will typically burn
for 6-7 hours.
On this day, I ran this system on an overcast
day to minimize the temperature increase from
solar gain.
The outside temperature was 29 and inside
was 55.
The air temperature above the first radiator
was 226 – keep in mind that the barrel temp
is exceeding 500 which is the limit of my
infrared thermometer.
The air drawn down before it reaches the fan
is 189, so some heat is radiating through
the cover heating the dome air.
After the air is drawn through the second
radiator, the temperature drops to 98 degrees
and it then enters under the floor.
The normal ground temperature for this area
is 52 degrees so the ground is acting like
a thermal mass and is currently at around
57 degrees.
Keeping the fan running while the heater isn’t
running helps to maintain the air temperature
at around 50 degrees during the night when
it drops below freezing outside.
The cover over the exhaust helps to heat the
air temperature to 94 while the exhaust vents
out of the building at 101 degrees.
The water entering the radiators is 60 but
exits at 81.4.
Hoping I did the math correctly, this equates
to using a 4.4kwh or 15,000BTU/hour to heat
the water.
The fish really enjoy bathing in the warm
water that’s coming in from the heater.
So far, the balance between heating the water,
floor, and air is working well, but the true
test will be when the weather gets really
cold in January.
Thanks for watching.
There will be more updates about the rocket
mass heater in the future!
