What am I not understanding?

[Ashkapp]

I have a Jotul F500 and I wonder why it is that sometimes I can get an amazingly hot fire going and can close down the draft, and other times I struggle and have to poke and prod it to barely get something going and that’s even leaving the door cracked. For hours.

It’s exactly the same wood and technique of building the fire. I am suspicious of this piece above the vent pipes- should it be sealed?

Thanks!

 

[bigealta]

Yeah that's not looking right.

 

[bigealta]

try a few more good pics

 

[Ashkapp]

Ok so in that picture I tried pushing it up and was able to scrape some loose creosote that had fallen from the chimney. This is how it looks in what I think is the proper position. (Sorry I had two photos and attached the wrong one)
There is a broken piece to this material (what is it?) but it still fits in the groove ok

 

[Sealcove]

If it is the flat surface at the top of the visible firebox, Google Jotul F500 baffle. It is a replaceable baffle section above the tubes for the air chamber/manifold system.

 

[Ashkapp]

So I’m guessing the correct position is to kind of seal off the chimney? It seems like the shape of it has a little bulge in the back to nestle down after the last pipe?

And my question about what makes the “heating” part of this stove actually kick in? In past older stoves, basically a cast iron box, once I build a fire it slowly heats up and radiates. This stove will exponentially heat it seems, but only sometimes. I’d like it to happen all the time but how? 🙂

 

[Sealcove]

So I’m guessing the correct position is to kind of seal off the chimney? It seems like the shape of it has a little bulge in the back to nestle down after the last pipe?

And my question about what makes the “heating” part of this stove actually kick in? In past older stoves, basically a cast iron box, once I build a fire it slowly heats up and radiates. This stove will exponentially heat it seems, but only sometimes. I’d like it to happen all the time but how? 🙂

Will give my two cents, but happy to have anyone else chime in or correct anything I say. I have been burning for 30+ years, but I don’t consider myself an expert on this by any means.

The baffle above the tubes in the firebox directs the heat and smoke around the front edge of the top of the firebox. I am sure someone here can describe it more properly, but in short it is part of the design to retain heat and have more complete secondary combustion around the top tubes. If that baffle is damaged significantly, it could be a reason for decreased stove performance. It is a part that does wear out and require replacement when I reaches end of lifespan. It sounds like yours may be at that point?

I have had a F500 and F600, and like with other stoves the general idea is get a hot fire going and as able, slow down air intake to retain heat (minimize how much you are sending up the chimney). Obviously it is a balancing act of not slowing the air intake down too quickly, but that all depends on the wood, one installation and the draft. An F500 should be pretty easy to get burning and heating well as it is a very simple stove.

How old is your stove? Are the gaskets all sealing properly and is the stove still tight? I let go of my last Jotul, the F600 because after about 12 years it was in need of a rebuild and I did not want to deal with it. I replaced all of the door and glass gaskets and found that I had air leaks in multiple places where the cast sections mate. Pretty typical for a stove that gets used (and it can be resealed if that is the case), but just mentioning in case you have an older stove. If that is the case, the stove may burn hot and fast with too much air available, but won’t have nearly as long or consistent burns. If that isn’t the case for yours, what is happening? Is it not burning well, are fires not getting hot? If so, what is the chimney and what are you burning?

Edit: Rereading your first post, I would just add that there can be variability in the woodpile and certainly weather and other factors will impact draft, but your results sound more extreme. Is there anything else in the house fighting the stove for air when it is not burning well? Heating system, bathroom fans, stove exhaust fan, ?