Most folks would use a fraction of that
if by "most folks" if you mean people who only have a woodburner to look good, or to be "green", and only light it now n again, when they're off work, you'd have a point. Otherwise you'd need a LOT of wood. If you take the cost of the stove and installation into account, it makes it an expensive luxury just to look good a few days a year.
If you light a logburner for 12 hours you're going to use about 1/7 of a cube, or a large wheelbarrow full, twice that for softwood, it's all relative.
and there is free wood you have to keep your eyes peeled,
I said there's no such thing as free logs, and I stand by that. If wood were really free there's be no fuel costs, or labor costs, to collect it, process it, and season it.
offer to step in with the saw when someone tips you off of a tree they want to get rid of
Do you have any idea how many professional tree surgeons are killed and seriously injured each year? If the tree is small enough for an amateur to cut down, there'd be next to no wood in it, if it does have enough wood in it to take on the job for the wood, is it worth your life? or the cost of replacing someones greenhouse/conservatory when you feck it up with no PL insurance? Is your time worth nothing? If not it's not free is it
and they deliver it for free too do they? If not it's not free is it?
my woodstore is half full of ash & birch, plus some conifer gathered this way
And how big is your woodstore? I suspect it holds 1 or 2 cube max, i.e. next to nowt.
yes you have to season it all apart from the ash
just because green ash will burn, doesn't mean you don't have to season it. Green Ash will not burn very efficiently, a lot of the energy will be used up driving the water out of it, therefore provide less heat - I know this because when I first installed our first log burner I could not get any seasoned logs for love nor money, so I got part seasoned ash (35% MC) and we froze for the whole winter. Burning green Ash in a smokeless zone will also attract fines if it's reported, regardless weather it is burnt in an approved appliance, wood over 20% MC will not burn efficiently, so you get smoke, whatever wood it is.
but I've only bought a couple of builders bags in the last two years to top it up, and I rarely use the central heating.
Whatever, gas is still cheaper than chasing round trying to find "free" wood at any meaningful quantity, or buying it in.
So I repeat, unless you have access to a LOT of free wood, gas is cheaper. This has been bashed out in numerous threads on Arbtalk over the last few years, the numbers don't lie.