I can’t remember what stoves you guys are running, and Tapatalk doesn’t show signatures, but the cat probe temperature and thermostat have nothing to do with one another on my BK’s. They may both be affected by the operation of fans, but not in any co-dependent way.
I have an AF30.0, one of the originals. I _think_ on mine the bimetal spring is heated by the steel firebox. When I run the fans, I am pulling heat out of the steel into the house, the bimetal "feels" colder and opens the air valve a bit to increase combustion rate.
The cat probe shows the temperature of the exhaust from the combustor,
yup. Only. The probe shows the temperature of the air at the combustor outlet. It does NOT indicate the cat is active, only if the cat is hot enough to be active if there is food available. I keep harping on this. If one of y'all want to fill a suitcase with seasoned white oak and fly up here with it as a checked bag, I got a spare room. If you come in January, i can show you the difference between a cat 1/3 up in the active zone but inactive on oak coals and how much heat comes out of a cat 1/3 up into the active zone and active on smoking spruce. You will be expected to come outdoors with me to consume Guinness at -30dF. Several of them, we can watch my stack plume and the northern lights and tell lies until the beer runs out.
and is easily affected by the fans in the Ashford 30’s, as the fans blow air right across the sensing shaft of the thermometer probe.
It is indeed possible to turn the fans off and see the cat probe creep back up into the active zone, under a limited number of conditions. A well seasoned operator, by the third winter or so of operation, should be able to avoid this. I think of it, going into my fifth heating season with the stove, as a preventable stall.
But but, the cat is active, it's just the fans causing the probe to read inactive when the cat is active. Mmmm-Hmmm. I judge that one by what outfit my wife is wearing. Fans or no, right or wrong, I keep my needle in the undisputed zone.
But the “thermostat” is a wound coil of memory metal or bimetallic that reacts to its local temperature at the back of the stove, completely separate from what the cat probe is doing or showing. The thermostat does not open or close to maintain anything, in terms of localized temperature at top of firebox or combustor probe temperature.
I agree. I think the tstat is heated by conduction from the steel firebox. Running the fans pulls heat off the steel into the room, less heat to conduct to the bimetal, air valve opens.
The probe going up when you turn off the fans may or may not have anything to do with any actual change in combustor temperature, it is affected by the air blowing directly across the thermometer shaft.a\
I do agree it is "possible" to have the combustor engaged, and the fan kit running, have an active combustor eating smoke and putting out the BTUs to prove it, and have the needle in the inactive zone. I also think that is a razor edge to walk on.
The actual thermocouple junction in the probe, at least on mine, looks to be pretty well centered on the back face of the cat. While airflow 5 cm away on the outer shield of the sensor will affect the indicator "a little", I struggle to see this as a significant factor at low and moderate fan speeds.
Weather forecast suggests tomorrow, yet again, will be a lovely day for a Guinness.
Still not too bad at 625! Closed it down after a while at 650, overall less stinky than expected.
