Smell's like coal!

Some woods smell different for sure. Seems like cottonwood was a stinky one.
I get something of a putrid burning smell sometimes when combustion isn't quite 100%. Put a little flame under three big splits and it'll smell like a campfire for a few minutes. Get those splits roaring and start to damper down and I've smelled what you're describing here.
Don't think I'd be worried about it.

I get the same thing here too. I burn alot of elm too.

I think my woodstove smells like coal when I am getting a nice, clean burn. I assume that is because the parts of the exhaust that smell like wood are being combusted, leaving an exhaust similar in makeup to a hot coal fire. I can't smell this inside, but I smell it in the yard.

I get that smell outside sometimes. Coal is a good description of the smell.

I've gotten that smell alot as well. I think Wood Duck is right about it being during a clean burn. Apparently the wood type doesn't make a huge difference there, as I burn pine all the time.

Right, I get that coaley smell when I've got a good burn going. I kind of like it....reminds me of days spent playing in my grandmother's yard. My grandfather heated with coal exclusively up until the 1990's. When he died, it was the first thing my grandmother changed. She was tired of rattling clinkers every morning and stoking the boiler...plus she kept her house spotless. With a bunker of coal in your cellar, that is not an easy standard to adhere to, let me tell ya.

Yep, clean burn. I have noticed that with both the Lopi and PE Summit regardless of what type of wood being burnt.

My bet is that sometimes, with a hot, clean fire going in the stove, the hot oxygen-rich gases in the flue react with whatever has been deposited there to give you a whiff of different fragrances. No real pattern to it, and nothing unpleasant.

Never smelled anything here resembling (bituminous?) coal here, though. Don't burn elm.