tar on chimney flue

Yup. Creosote. As long as it is not flaky and crusty you probably do not have to worry. Our old chimney was like that on about the top 4 feet and was like that for many years. We simply did not worry; just cleaned the chimney as normal. However, pay extra attention to the cap as that will build up with flaky sooty stuff and sometimes needs to be cleaned a couple times during the winter.

Also, you are burning dead elm. Does that mean you are burning it without seasoning? If so, that is what is causing the tar. Even though the elm is dead and the bark has fallen off, that stuff still has moisture in it and will cause lots of creosote. Better to cut this year to burn next year. btw, we also burn a lot of dead elm. Cut a couple of them this winter and will cut a couple more yet this Spring if this snow and ice ever melts.

You are right. That elm is all over Michigan. It pains me to drive down the roads and see dead trees all over the place and nobody taking advantage of it.

Sounds like you have the right idea with what you cut this winter. I wasn't able to cut much because of the deep snow, but we have over 5 years on hand anyway so I won't worry.

And we also have a whole bunch of dying white ash now, compliments of the Asian ash borer. Woods really look sick.

Yes, you should. Keeps the weather out and stops most of any possible downdrafts.

also keeps critters out.

when I was a kid we decided we wanted to start having occasional fires in the old masonry fire places in our 20's built home. The fireplaces had not been used in many years, so my folks had a chimney sweep come out and clean / inspect the chimneys.

Darned good thing they thought ahead -- the sweep found 14 dead blackbirds in the upper portions of the flue!

The chimneys had no caps, the birds got drunk eating the fermenting mulberries from the neighbors tree - and fell down the flue pipes!

We also had the occasional squirrel fall in.

Best to have a cap - and best it be stainless on the stove chimney.

You guys have piqued my interest - so far I've not heard or seen any dead Elm - I'm near Ann Arbor - perhaps there aren't many of those around here - but boy do we have a lot of dead ash!