Gridlock said:Thanks for the suggestion. I tried not blocking the cat chamber float last night and this morning, and it did help, though not sure if the reason it worked better was not blocking the throat, or because there was less wood in the firebox due to leaving the space clear next to the throat! It also still took substantially longer for the CAT temp to rise substantially, as compared to a somewhat smaller load. The more I think about it, Henk's theory above really makes a lot of sense.Todd said:I wonder if during a reload you raked all the coals towards the back where the cat chamber is located and pile the wood on top if it would make a difference? Those VC's have that rear chamber cat design where I could see air flow getting restricted from solid wood up against it. If there was a good pile of coals the air might have a better chance getting up through there?
Thanks for the vote of confidence for one of my many theories, Gridlock, let's call it theory 2.0 (i.e. larger loads may be producing a higher proportion of water vapor at the specific point in time that you close the updraft bypass flow. This followed my (alas a bit too flippantly posited) theory 1.0 (i.e. larger loads go through a longer endothermic phase). Both 1.0 and 2.0 were generic theories, in the sense that they pretty much apply to any type of cat stove.
Then Fire God Todd spoke and made me realize that your stove is definitely not "any type of cat stove", thereby prompting me to study the online manual of your stove in order to see how much of what I had theorized about was applicable at all.
This spawned new versions of both theories; let's call them 1.1 (i.e. the longer heat-up times for larger loads might be less pronounced at the stove-top than at the catalyst top) and 2.1 (i.e. the large amounts of water vapor produced by larger loads could already deactivate the cat during the early heat-up phase), as discussed in my previous post.
Since the 1.1. version seems to resonate with the testimonies and views of several other posters who actually have an identical or similar type of stove as you have, my money is presently on the idea that with larger loads your stove top temperature may be way too optimistic and you should probably try to measure your cat top temperature more directly (or, if you do so already, at least re-calibrate the probe).
Please also remember that your stove manufacturer advises to start the cat at 450 F.....
Best of luck,
Henk