Woodburning stoves: what wood and why?

Question

I have been experimenting with a very old (made and installed in the 60s) woodburning stove in my new house in Devon, UK. I have started to learn that hardwood burns for longer than softwood, that well seasoned wood burns more quickly and more cleanly (it releases less creosote). Unfortunately my chimney doesn't have a flue all the way to the top, and the landlord doesn't seem to be interested in installing one soon. This may be one of the causes of my temperatures (around 100-200 C) which do not take off easily.

I would like to ask for references that describe in detail the properties of different firewoods, comparing several species of UK trees. I haven't been able to find such a reference. I have read The woodburner's companion but it doesn't contain any discussion of wood selection.

Answer 1

https://chimneysweeponline.com/howood.htm lists the energy content of a wide range of wood types.

Some examples that are perhaps relevant to you:

• Beech, Blue (Carpinus caroliniana): 23.7 MBTU/cord
• Ash, Black (Fraxinus nigra): 17.9 MBTU/cord
• Sycamore, American (Platanus occidentalis): 17.9 MBTU/cord
• Larch (Larix laricina): 19.5 MBTU/cord
• Cottonwood (Populus trichocarpa): 12.6 MBTU/cord

Also note that Ash is well-known for its low moisture content even when green and so typically requires much less seasoning than other species.

It may also be that, given the age of your woodburning stove, the species of wood you burn isn't the most important factor. Wood stoves of the era you refer to are typically dirty and inefficient compared to modern wood stoves (which themselves are fairly dirty and inefficient).

Also bear in mind that creosote isn't just a sign of inefficiency but is a major safety hazard. If you often burn low temperature fires, and particularly if you burn unseasoned wood, creosote can build up in the chimney (flue or no) and result in a chimney fire (which can burn your house down, shake your chimney down, and generally ruin your day).

Make sure you've studied up on the safety considerations that go with operating a wood stove. Perhaps also consider replacing your current stove with a safer model - perhaps something like a rocket mass heater.

Answer 2

I don't have enough reputation yet to write a comment, so don't see this as an answer, more like a recommendation. I grew up with a wood stove, so maybe I can help.

This may be one of the causes of my temperatures (around 100-200 C) which do not take off easily.

That is definitely not a good temperature to burn wood. You want the fire to be >300°C for a clean, efficient burn. As you noted, hardwood burns longer than softwood, but it is also harder to get started. I'd start the fire with soft wood. It's much easier to get a blazing fire that way. Once your stove is up to temperature, switch to hardwood. If your fire ist still misbehaving (as it sometimes does for me with certain weather conditions), you can add a log of softwood every now and then to keep it up.

Answer 3

Native timber species (that just might be offered to you) as fuel (all 5% moisture):

• Beech 17Mj/kg
• Oak 16MJ/kg
• Pine 17MJ/kg

(BTU/cord would be little understood in these islands)

Remember that pine is substantially less dense than the hardwoods

A source for the info: UN FOOD AND AGRICULTURE ORG WOOD FUELS HANDBOOK

Most important: CLEAN YOUR CHIMNEY!

As pointed out in other posts, soot buildup is a serious fire hazard.

btw, "flue" is the same as "chimney". I suspect that when you state that your "flue doesn't go all the way to the top...", you actually mean that the stove pipe (the pipe that connects your stove to the flue) feeds into a chimney.

What you want to achieve is a sealed system with all air entering through the air intake of the stove, and existing at the top of the chimney. The allows all the air entering the system to be directly available to the burning timber. Ensure that the seal around the stovepipe is good and that the flue has only one outlet (at the roof level). You can seal any dodgy joints with fire cement, available in cans. This should improve the "draw" in the flue. Ensure that all door seals are good. Install new sealing rope if necessary.