Cottonwood yesterday. Splits like hell, But was free and will make heat! The rest is a mix of ash, cherry, and honey locust Sent from my SM-G892A using Tapatalk
Hmm, cottonwood. Not the most desirable of species from a BTU perspective, they tell me. But as you say, it'll produce heat. We have a number of medium density eucalypts around here, oakish to locustish, and a few of them have very little ash but the densest of them (blue gum) has quite a lot. Of what is available, I'd burn manna gum which has virtually no ash in the heartwood (it's all in the bark, so you want to get rid of that). So, big manna gum is now my favourite for firewood, followed by peppermint. But I'd burn cottonwood as long as it doesn't make a big mess.
For daytime burning, I'd burn anything that doesn't bung up the heater with ash. Night-time, well, you need the BTUs so I put up with the ash.