A modification to my gravity feed wood pellet rocket stove. In order to reduce the amount of wood pellets consumed, I thought I would add the option of burning ‘real wood’ along side the pellets.
I had tested the theory of a dual fuel rocket stove by adding sticks into the fire box. Repeating at 10 minute intervals. This involved getting down on hands and knees to insert small sticks into the combustion area.
By doing this I was able to reduce the quantity of wood pellets burned in half, while maintaining heat output.
The main problem was the interval at which wood would need to be loaded. The reason for building the pellet rocket stove in the first place was to be able to load it, light it and forget about it. If I was going to have to add wood every 10 minutes it would be pointless.
Lengthening the fire box
This is the modification that I came up with for converting the pellet rocket stove into a dual fuel rocket stove.
Because of the minimal cost and time involved to carry out the modification, I thought it must be worth a try. After all, if I could save a bag of pellets a day with a dual fuel rocket stove, it would save a small fortune over the course of the winter.
This is where the modular design of the fire box is really handy. I extended the original fire box, doubling it in length, leaving a 10cm square hole in the top. This allows for the mounting of a wood supply tube.
After making up 4 new angle iron straps, as shown in the photo above, the fire box unit was ready to be re-assembled.
The top fire brick was cut to leave the 10cm hole required.
The whole modification only took 4 hours, including then dismantling and re-assembly, at a cost of under 25€!
After a couple of weeks in operation, the result of the dual fuel rocket stove is very promising. I’ve cut wood pellet consumption in half, a 15kg bag now does about 24hrs.
I have made a temporary wood supply pipe from a short piece of flue pipe. It works ok for testing purposes, but really needs to be more solid in its construction. Also the addition of proper fireproof seals would be a good idea.
With the current temporary feed pipe enough wood can be added to allow a 30 to 40 min burn. So I think with the addition of a longer one, going to try 1 metre, the 60-90 min re-loading interval should be achievable.
This modification has turned out to be very practical. The dual fuel rocket stove burns pellets continuously, supplying a base heat for the underfloor heating. And when I’m at home I can add wood to give it a boost.