Dave Liquorice wrote:
2nd Year of running the woodburner. Didn't think it was drawing very
well the last few days, wasn't sure if it was because of the cold,
still, weather or something else. So removed the baffle to look at
the base of the 7" rear exit flue. Maybe more than 50% blocked by
light crispy/brittle tar bits, removed all that (a bucket full) and
it's now drawing and burning far better. B-)

The flue was swept before we started this season in the last week of
October, similar amount of burnt tar then after the entire winter (5
months?) as I've just removed after a week under three months.

There has been a fire in it most days since the 23rd Oct from about
1500 with the last logs going in about 2100. The stove is quite large
10kW output but with a boiler rated aroud 7kW so I guess the flue
gases are generally quite cool. We are burning seasoned hard wood
(mostly beech but some birch and a little possibly oak), with the
bark falling off and shakes opening up in the end grain. Generally
it'll get through 4 x 9" long 4" sized logs every hour, so something
over 15 logs/day.

Is that level of light crispy tar build up sort of expected? I don't
mind digging it out every 6 weeks or so, more concerned about buildup
in the flue and risk of a fire up there...

I've got a woodburner, multifuel actually, but I wouldn't describe myself as
a guru.
It's been installed since Oct 2011, so just over a year. I burn mainly scrap
timber - door frames, windows, joists etc, the occasional tree (cherry,
eucalyptus, oak, sycamore) and a little coal.
I don't have a damper, the hole at the back of the burner has a 5ft piece of
corrugated flue liner affixed to it and bent up into the (brick) chimney,
draws well with vents open, smoulders for hours unvented and I've never had
any build up of tar/ creosote.
It's used daily from Oct to April, from about 5pm to midnight, using about
same volume of timber as you, but this time of year, a kilo of housecoal
gives off a hell of a lot more heat than wood alone, I pay £7.50 for a 25kg
sack, so about 4 or 5 will last me over winter, **** the smokeless ****e
off, and the stuff the garages try to sell at £9 for 10kg