Harbor Freight 10 x 12 Greenhouse Build

[Hiester]

It has been fascinating to watch the progress of your new greenhouse. I have a 10x15' foundation already available, so seeing what you and your spouse have done here is definitely an inspiration to go forward with plans for a greenhouse of my own.

I want to learn much more about the rocket jet furnace. I'm wondering if it would burn pellets... maybe if it had a grate? There was a similar type of heating apparatus in the German House (cabin) of the Frontier Village near Staunton, Virginia (a museum of frontier culture), so the "technology" for such has been around for a very long time.

[shadytrake]

Originally Posted by Hiester

It has been fascinating to watch the progress of your new greenhouse. I have a 10x15' foundation already available, so seeing what you and your spouse have done here is definitely an inspiration to go forward with plans for a greenhouse of my own.

I want to learn much more about the rocket jet furnace. I'm wondering if it would burn pellets... maybe if it had a grate? There was a similar type of heating apparatus in the German House (cabin) of the Frontier Village near Staunton, Virginia (a museum of frontier culture), so the "technology" for such has been around for a very long time.

Hi there and thanks! Yes it will burn pellets, but there is more ash build up. Check out Zero Fossil Fuel's videos on YouTube. He did extensive experiments with pellets for the Rocket Stove.

He doesn't use a thermal mass, because he is only interested in the radiant heat from the stove. However, his design is excellent and we used it as a model for our setup.

We won't use pellets this year, but if we don't get the expected burn we may use them next season. There is quite a bit of planning required for pellets because of the buildup of ash and the burn pattern. They don't burn vertically so there is the possibility of jamming in the feed tube.

https://www.youtube.com/user/ZeroFossilFuel

We expect to build the stove tomorrow if the weather holds. I will take lots of photos and will try to get all the measurements that we use. One of the things that is so frustrating about researching these is the lack of measurement posting. Yes, it does require experimenting and is not an exact science, however basic measurements and design are the same for most builds.

[shadytrake]

More updates as we get to the home stretch. We have completed 1/2 of the rocket mass heater. Once the refractory cement dries, I will be able to finish the build and we can put the heat riser together. Here are pictures.

[My Green Pets]

Looks amazing!

Noob Question: I have seen builds where the exhaust duct loops back through the mass a couple of times instead of just one run through as in yours. Will this affect the amount of heat transferred to the mass before it is blown out the exhaust?

[shadytrake]

Originally Posted by CambriaWhat

Looks amazing!

Noob Question: I have seen builds where the exhaust duct loops back through the mass a couple of times instead of just one run through as in yours. Will this affect the amount of heat transferred to the mass before it is blown out the exhaust?

It shouldn't. The reason they do that is to create a couch or a bed with no cold spots. Mine is just a narrow run through the GH so looping back is not needed.

I started the build on the heat riser today and we go the load of pea gravel for the thermal mass.

[shadytrake]

Almost ready for firing it up!

[My Green Pets]

Awesome! I have only seen heat risers made of metal tubes insulated with perlite and clay. Will the brick and mortar version reach the required temps?

Also, how big is the gap between top of the heat riser and the steel drum placed over it? I have read it needs to be 1.5 - 2 inches.

Learning so much here! Thank you!

[shadytrake]

Originally Posted by CambriaWhat

Awesome! I have only seen heat risers made of metal tubes insulated with perlite and clay. Will the brick and mortar version reach the required temps?

Also, how big is the gap between top of the heat riser and the steel drum placed over it? I have read it needs to be 1.5 - 2 inches.

Learning so much here! Thank you!

Hi Cambria,

The heat riser will have a 10" tube surrounding it packed with perlite for insulation. That will be tonight's project if my back will stop with the spasms. The top will be slanted inward to encourage any ash to fall into the burn chamber rather than into the barrel. Our gap at the top will be about 3" because we don't plan on cooking. The small gap is for being able to put a tea kettle on top for cooking and for extra radiant heat. We really want the heat in the thermal mass rather than as radiant. Radiant heat though quicker at the barrel dissipates much too quickly in the GH. It is more efficient if slowly released by the thermal mass.

Yes, to answer your question about the temperature. It will reach the required temps. Most heat risers are built with brick and fire brick is recommended because of the extreme temps produced. Here are videos of our test run last night (to cure the refractory cement).

Built RMH 1 - YouTube
Built RMH 2 - YouTube
Built RMH 3 - YouTube
Built RMH 4 - YouTube
Built RMH 5 - YouTube

[My Green Pets]

Great videos!

I was wondering about the little hole at the bottom, thanks for the explanation! From what I've seen here and in other places, this type of stove has lots of room for customization and tinkering.

Looking forward to the next update...

[shadytrake]

Insulation tube installed! Tomorrow we round it off with refractory and trim. Then we should be able to finish the heater and proceed to finishing the shelves.