Accepted Answer

Hello and thank you for your question.

One possibility is that the screen at the top of the chimney has become clogged with particles. This can happen if the screen mesh is dense. Ideally the screen mesh should be just small enough to keep out birds.

It does not sound as though the problem is likely to be with the stove itself. The Oslo model is known to be prone to a problem with the damper handle that can make the damper difficult to operate - sometimes it will cause the damper to fail to open or close fully. But this is not likely to come on suddenly, and is more likely to be present in a new stove - but it wouldn't hurt to inspect the damper operation to make sure that it is not stuck or failing to open sufficiently. If this does turn out to be part of the problem, it should be addressed with Jotul directly as it will often require replacement parts, though applying graphite to any areas that appear to be sticking may help in the short term.

Many problems with smoking are due to a lack of combustion air or differences between indoor/outdoor air pressure. But this seems unlikely in your case as things have operated well until just recently. Unless you've done something very recently that would have significantly reduced available combustion air (did you just insulate the home? replace windows and doors? add a lot of weatherstripping and caulk? anything like that?) it just doesn't seem likely that these conditions would have changed enough to create the problem.
Geographical issues, and even very tall, dense trees or buildings nearby can all cause issues with air flow, but unless these conditions have changed drastically and recently they're also unlikely to be related.

So I have to suspect that the problem is either a clogged screen or an obstruction within the chimney. Either would best be addressed by CSIA-Certified chimney person.

I hope this information helps, and if so that you will please click the ACCEPT icon as this is how I get paid for my time answering questions.
Please feel free to ask additional related questions.
Thank you.

Expert:	MJ
Pos. Feedback:	100.0 %
Accepts:
Answered:	12/21/2008

Architect, Efficiency C&onsultant

Licensed Architect, LEED AP, Energy Efficiency Consultant