Any hot air furnace experts in north east NY?

Good, glad to hear its working better with a simple chimney height solution...

 

The 526 has a smoke bypass only. No secondary heat chamber. You can easily check/clean it from the furnace door. The 2 larger models have secondary chambers.
First 2 years I had mine it was on a short chimney. Worked well and burned clean. Moved it to a different location in house and now it has a 17' chimney. Has given me fits the last 12 years from burning straight beech . Ended up buying 2 brushes and pipe unioned them together. Cleans well but I'm getting to the age where I don't like getting on the roof.
Wood supply changed last year and its mostly oak now. Burns cleaner but still has issues.Just longer times between cleaning. Have used every known chimney cleaning myth and product on the market. This winter by dumb luck I found a chimney cleaner that works and use it every 2 weeks or so. Have only been on the roof once this year ,, before dumb luck and I met.

 

Yes, it is definitely is a smoke bypass...but when it is in 'bypass' position, what is it bypassing ? Isn't it bypassing an additional chamber on top of the main heat exchanger to allow the fire to draft real well during start up? Then after the fire is established and the bypass is closed the smoke has to travel back towards the front of the main chamber and up into the additional chamber before reversing direction again to vent out the rear....creating that serpentine effect and giving it the chance to extract more heat....(??)

The larger ones may not have the bypass gate like the 526 but I think they have the same basic design overall except for dimension changes in firebox, footprint and cfm.

No contrariness here, just a devil's advocate, I think we are pretty much saying the same thing we just ain't using the same words....

I'm right there with you on the roof thing....I have standing seam metal and its so slick you can barely walk on either side of the ridgecap much less carry the brush and handles. So I have to put up a 32' extension ladder to get to the top of a 26' brick chimney !!! THEN its really a major balancing act and not fun at all.... But I do use conduit and conduit connectors instead of the heavier pipe. I need magnetic shoes....

 

I would call it an internal extension of the chimney. It's inside the firebox and provides no extra heat. The larger models have a heavy pipe that runs up from the front of the firebox into the plenum area and out the back extracting heat from the chimney into the plenum.
Other than a smoke bypass on the 526 I can't see any heat gain from it.