Eucalyptus wood in Rocket Mass Heater

My client (https://permies.com/t/281004/Lightweight-Rocket-Mass-Heater-Mediterranean) has a lot of eucalyptus on her property.
It’s invasive and flammable, so she has to control it and cut and collect all windfall ect.
Someone told her it’s not good for burning in wood stoves.
I couldn’t find anything online that said it wasn’t ok to burn it.
Any permies here with experience using eucalyptus wood as fuel? We just want to be sure not to ruin her freshly built rocket.

As I understand it, the reason it's not recommended is because it burns hot and fast and most people want a much slower burn in a wood stove so that it gives heat out over a longer period.

In a rocket mass heater, however, a fast and hot burn is exactly what you want! No need for a long slow burn as the mass absorbs the heat and gives it out over a long time.

We regularly burn eucalyptus. Or acacia (mimosa). Or sticks that other people leave behind when they cut big trees. Or junk wood salvaged from building sites. Wombling other people's left-over wood that they've left behind because it's not considered good enough, getting free heat out of it, and leaving the place more fire-proof is one of the things I love about having a rocket mass heater.

The bark makes a pretty volatile fire-starter too!

Hi Ben;
I looked it up and found that yes, eucalyptus is a hot-burning wood.
However, it absolutely must be below 20% moisture content.
Apparently, it is hard to split when dry, and it is suggested to split green.
If attempting to burn this wood unseasoned, you will have problems.
It puts out a thick white smoke, it sparks and pops, from the oils it releases, and it can cause creosote buildup in the chimney.

So, with a hot burning J-Tube and seasoned wood, it sounds like eucalyptus is a fine choice to clear off her property.

I can look out of my window and see four different  varieties of Eucalyptus and I live as far away from Australia as it is possible to be, but I believe there are over 600 different forms.
As an avid didgeridoo builder I can confirm that the species has an amazing range of different textures and hardness depending on the species! In any case I would not worry about burning any of them in a rocket stove.  

Also, from experience, it's very hard to kill.

You cut it down and ten more 'heads' grow up from the stump. Which, however, make it an awesome tree to coppice if you're prepared to have it on your property at all. In a couple of years you have a load more stems to cut, which will be small enough to not need splitting. We had a few enormous ones up in the forest above the house that burned in the fire a couple of years ago and we felled most of them. Still have to go and haul the wood out, but I bet by now they're busy re-growing.

I dug some photos out...

This photo is of some that were growing at my last place. The bark falls off and leaves strips of incredibly volatile fire-starting material all around. The leaves are just as bad too. It's an amazing resource but a crazy fire risk.



These eucalyptus were cut two years previously and are regrowing. This is a commercial plantation, for paper, and in the next year or two most of those new stems will be cut off, leaving the best one to grow for around ten years. After which it is cut again. They would make excellent firewood coppice if you lived somewhere that wasn't so prone to catching fire in the summer.



This photo is a stump that was cut, then cut again the next year, and the next and the next. After about four years, it finally gave up.



This is a eucalyptus branch that was left behind after someone felled a tree near a forest track. It's a terrible fire risk, so we helped by taking it home and burning it on the rocket mass heater.



And this is a clump growing on the mountain above the house, which got burned in the fire. We don't really want them there so they got cut down. Or most of them at least, I suspect there's still a few left. This photo was taken just a few weeks after the fire, after the first rain which meant it was safe to go and cut. The stuff is already attempting to regrow. Most trees I'm happy to see coming back to life after the fire, but not this stuff!

I burn eucalyptus (camaldulensis also called River Red Gum) and only eucalyptus, because these are the only trees that I have on my property for that purpose.
I have around 100 m3 of firewood cut to 40 cm length with diameters from 5 - 30 cm and 50 m3 of roots.
It's specific gravity in fresh state is over 1, so it will sink in water. When dry it's around 0.9.


Chopping:

It has to be split when dry. Having a lot of moisture it cracks badly, and it helps to split it with manual tools - it's good to have synthetic ax handles, as the wooden ones will be broken in hours because it needs so much force to split. For cutting it crosswise I use a metal chop saw with carbide tipped blade. Chains in chainsaw get gummed quickly from excessive sap. I have used the same blade for 10 years.


Burning:

It has similar caloric value to other hardwoods, however - being so dense it means you can not stuff your firebox to the brim, like with light northern species, because fuel load will be too high and it will smoke - similar problem to burning long hydrocarbon plastics.
For best results I load my bread oven firebox with only half of its volume. I don't have a secondary air tube and it would probably help.
Most oils are in leaves. I never smelled any hint of eucalyptus fragrance in the wood. I never observed sparking when burning wet or dry pieces.
Since it's dense, it leaves a lot of coals, especially if thicker (over 8 cm) parts were loaded or when I use even denser roots. Because of that it helps to have grills in cooking stove fireboxes. It burns better on the grill than on firebrick, resembling coal or coke for which grills are always used in masonry heaters.

I also mill it (very difficult to get usable lumber), use it for fence posts, mulch, smoking, forging and my sheep love the leaves - green and dry.

Re the creosote build up - as long as the chimney is "straight through"
i.e. no angled bends, there should be no problems.  Ours has been going strong for over 30 years.   Neighbours with a right-angle bend had a chimney fire requiring the fire dept.  The wood does burn hot though and we have an hydraulic splitter.

Thanks everyone!
I knew that permies would have the answer.

Can confirm, properly dry eucalyptus is excellent rocket fuel.  

As for splitting it tends to have a twisty spiral grain so it doesn't split straight, also it tends to make little thin bits that try to join the 2 parts you are attempting to split.  It is easier split when green.  I recommend a hydraulic log splitter, biggish logs are a mare to do with an axe or wedges.  Good exercise I suppose...

If you spot anyone replacing old tiled roofs, the beams were often eucalyptus as it grows straight, is fairly strong, and somewhat resistant to rot.  Old roof beams (aside from the nails they contain) are a superb source so worth trying to make a deal for them.

If you have mimosa/acacia where you live that is also invasive and is also good fuel, and dries quite fast as well.