Jotul F3 - What is the "Air Blocker" for?

[Pellet_Pete]

The caveat for the new-to-me F3 I just got from craigslist is that I must replace the secondary air manifold due to warping (accounted for in price). So I've just figured out (thanks to hearth.com of course) how to remove the top of the stove for ease of access. This allowed me to unbolt the stove pipe adapter & then remove the rear heat shields, and finally get at the screws that bolt the secondary air manifold to the stove. One of these screws/bolts also holds on the secondary air intake cover, and a weird piece of cast iron fell out when I removed the cover.


According to the spare parts listing from the Jotul UK site, this is part #84 on the diagram in the manual, which is listed as the "Air Blocker (for USA)". Apparently it serves the function of restricting the secondary air intake area, as below:



So the question is, why this constriction?

As an aside, that little bit of secondary intake was partially obstructed by gasket material & cement, so when I re-gasket the manifold it will be better than new.

 

[begreen]

That's a very interesting discovery! Our F400 came with a European doghouse that admitted more air. It's also interesting to note that we have a person here from Scotland whose F3CB was burning hot. She had to restrict the secondary a bit to tame it down.

 

[Pellet_Pete]

That's a very interesting discovery! Our F400 came with a European doghouse that admitted more air. It's also interesting to note that we have a person here from Scotland whose F3CB was burning hot. She had to restrict the secondary a bit to tame it down.

So do you think it's a good thing, allowing for better burn control? It seems like a safe/conservative approach, to place a physical limit on the non-adjustable intake air, since you can always increase air via the primary.

 

[Pellet_Pete]

Just found this unanswered thread on the same subject from our Scottish counterpart!
https://www.hearth.com/talk/threads...fication-to-jotul-secondary-air-inlet.141146/

 

[FionaD]

Aye!

 

[ToltingColtAcres]

So do you think it's a good thing, allowing for better burn control? It seems like a safe/conservative approach, to place a physical limit on the non-adjustable intake air, since you can always increase air via the primary.

if that's the case, why not simply reduce the size of the non-adjustable air intake from the onset to place that 'physical limit'?

 

[FionaD]

My curiosity is really getting to me over this. Please someone call Jotul USA and ask them.. Then report back to us here!

The only thing I could think of was that it seems that stovers on the left side of the pond really fill their stoves to the very brim, whereas folk over here don't seem to do that, as far as I have seen. So maybe Jotul USA needed to reduce the draw to avoid potential overfiring - is that a possibility?

 

[begreen]

My guess is that it has more to do with how the stoves are emissions tested in Europe vs the states.

FWIW, 3 splits fills that little stove to the brim.

 

[BrotherBart]

I have ten bucks that says it is to adjust for the fact that in the U.S. they have to use a six inch pipe and a specific flue height for EPA cert. Whereas in Europe they use the smaller pipe.

 

[begreen]

Not a betting man, but in Europe the F3 series ships with a 150mm (5.9") flue collar, same as in the US.