Hey, Ravenswood...
As I was watching, a strong just of wind hit the house, and the firebox went dark! Smoke started pouring out of the intake dampers too. When the gust ended - WHOOSH, instant flaming hot firebox! Just like someone had hit a switch.
You didn't mention whether or not you have an OAK on your unit. If you do, that may be the culprit - NOT the cap.
Think about your description of the events - they're printed between the arrowheads above...
I quote, "The firebox went dark..." I would ask my self "Why? What could cause THAT to happen?
Your fire is burning nicely - so you have the three ingredients for fire...
1: Heat source
2: Oxygen &
3: Fuel...
If wind came down the chimney, it would add MORE OXYGEN.
On the other hand, IF the position of the OAK hood (or intake) was caught by the blast of wind in such a way, that instead of pushing air into the OAK,
it created a venturi effect & sucked air OUT of the OAK what would happen?
Loss of combustion air - OXYGEN - in the firebox, would cause the fire to go out...
When the wind died (or changed direction) the correctly drafting chimney system sucked more combustion air - OXYGEN - into the firebox &
I quote, " WHOOSH, instant flaming hot firebox! Just like someone had hit a switch..."
Ok...I'll admit to barely passing college physics, so I can't put this into a legible scientific formula, but it CAN & DOES happen.
It was proven a couple of years ago by
www.woodheat.org & that proof caused Canada to drop OAK mandates.
Course that proof don't mean squat round these parts...
If you DON'T have an OAK, I didn't say anything.... :red: