EPA stove overfire... Any changes to regulations? Flue liner size change?

[SuperJ]

For your volume calc, I think your diameter should be the 3/8"s hole in the thermostat blade (or whatever the smallest orifice), not the diameter of the vent pipe. You aren't feeding your stove with a 6" diameter air inlet. But, it would be interesting to use some sort of pitot tube setup to try and determine flow based on velocity and diameter.

 

[SuperJ]

Thats why I have a big tech boner for the fully automated control system I linked.... Ya its over over engineered in typical german fashion but it controls inlet air, fans, flue gas temp, flue barometic pressure, the works.

Ultimately I think this might be the future, with thermal electric generators and a small battery you could probably run the whole thing without plugging it in to an external power source.

 

[begreen]

Thermocouples in multiple locations are typically used for automated control, but there are some innovative techniques also being shown that explore other options. Ideally an O2 sensor would be employed too, but that gets pricey.

 

[SuperJ]

Is there a way to confirm the the thermostat is actually closing under overfire/high temp conditions? On a free standing stove you can remove the cover and observe the thermostat action. If it's actually closing then looking for air leaks, and controlling the draft are the obvious things, but if it's not responding then the thermostat itself deserves closer scrutiny.

If it's not closing... How is the thermostat coupled to the princess insert? If it's fasteners you might want to remove and and check the surfaces for good contact (maybe even install some sort of malleable thermally conductive interface like thin copper, or high temp thermal paste).

 

[begreen]

Yes, there are some long postings in the BK performance and maintenance thread on this topic.

 

[sadpanda]

Thermocouples in multiple locations are typically used for automated control, but there are some innovative techniques also being shown that explore other options. Ideally an O2 sensor would be employed too, but that gets pricey.

Yes thats why my collar adapter already has an O2 sensor bung welded on it and there is a WBO2 sensor kit sitting on my desk right now


yes you can observe the thermostat. It simply does not shut down the air inlet enough. This design is a coiled bimetalic spring that is shaft mounted near the side wall of the fire box but does not touch it. Shaft changes the clocking of the spring, free end of spring has a chain hanging from it that is connected to an air inlet flap. Stove heats spring, spring relaxes and closes door. Room air cools spring, spring tightens and opens door.

When I was getting overdraft/overfire the firebox was full and looked borderline rocket heater ish... Flames getting sucked through the cat, cat glowing like sword being forged, stove poping and pinging like a car exhaust... it was glorious lol. In that situation I think the cat/top plate/exhaust collar and pipe are taking all the heat literally and figuratively. The firebox side walls are not heat soaking at the normal rate so the spring cant do its job. Really, having the spring sitting on top of the cat (and calibrated accordingly) would probably be more ideal but that would probably make mechanics/packaging 'difficult'

 

[black smoke signals]

Sad panda said yes you can observe the thermostat. It simply does not shut down the air enough.—————— I’m thinking if the 3/8 hole was not in the flap with high winds the flap would be jumping (flapping) against its stop. Would this snuff the fire out (I’m not gonna try it on my stove) or at least slow it down? My over fire only happened once when wind picks up 45-65 mph. Also has scared wife loading from a cold stove because t-stat is not allowed to go to full shut down in case of high wind alert she just didn’t feel like she has control over the stove. Don’t get me wrong I think it’s a good heater but sometimes we have to be carful as the wind can be unpredictable

 

[BKVP]

One of the designs at the Alliance for Green Heat 2018 Wood Stove Design Challenge has an option for this exact issue. The problem with the EPA tests is that they are with a fixed chimney height of 15'. That only covers the average single story home and not all the other normal variations from mobile homes, basement installs and 2 story with an attic.

I know it all too well. The dilution tunnel is not even externally vented! It's vented into a draft hood, within the room and can have velocity controlled by a fan/rheostat.

 

[SuperJ]

yes you can observe the thermostat. It simply does not shut down the air inlet enough.

Do you mean it fully closes but still permits enough air to overfire, or do you mean that it never fully closes, even under over fire.

 

[sadpanda]

I have used 5.5 a few times because of space limitations. But i will not do it on a chimney under 25'. Because of that i have never had an issue. Another point to add is going down to 5.5 wont change the pressure measured by a manometer. It will change how the stove runs because it changes the volume and velocity in the stack but the pressure will not noticably change.

I agree the pressure will not noticeably change. I'm having a draft issue which means I'm having a volume and velocity issue. The stove was probably designed by starting with the target emissions rate and the test parameters (draft) and the mass air flow requirement resulted in a 6in flue. Hence the King needing an 8in.

I'm exceeding the draft so my velocity and mass air flow is too high. I need the restriction to bring the mass air flow back in line yes? I'm currently doing it with a key damper but I'm thinking that causes other issues ie too low of a velocity for the the given pipe size

Like I said, there most certainly must be some sort of calculation that is run for this sort of thing. https://www.mecaflux.com/en/calculer conduit fumees.htm ?

I'm having to order 24' of flue liner so I think I'm in that range...

 

[begreen]

Is there anything pressurizing the stove room? HRV imbalance?

 

[sadpanda]

Do you mean it fully closes but still permits enough air to overfire, or do you mean that it never fully closes, even under over fire.

I'm saying it does not fully close. Again, unless the spring proves faulty, I'm thinking there is enough of blast furnace effect with the down wash air delivery that the cat/top plate/flue is heating soaking WAY faster then the side wall where the thermostat is located. That side walls have shielding inside the firebox as well so the thermostat is quite insulated from whats going on. I was IR gunning the stove all over the place in the beginning... I need to look back in my emails but I think there was a HUGE difference from the top plate temp by the cat and the side wall right by the thermostat. Like 500F difference.

 

[bholler]

I'm saying it does not fully close. Again, unless the spring proves faulty, I'm thinking there is enough of blast furnace effect with the down wash air delivery that the cat/top plate/flue is heating soaking WAY faster then the side wall where the thermostat is located. That side walls have shielding inside the firebox as well so the thermostat is quite insulated from whats going on. I was IR gunning the stove all over the place in the beginning... I need to look back in my emails but I think there was a HUGE difference from the top plate temp by the cat and the side wall right by the thermostat. Like 500F difference.

The problem with this theory is many people run princess inserts on chimneys as high or higher than your chimney. Few people have issues with their inserts which tells us there is something more going on with yours. Have you had anyone there to check the thermostat? It really sounds like it is not functioning properly.

 

[bholler]

I agree the pressure will not noticeably change. I'm having a draft issue which means I'm having a volume and velocity issue. The stove was probably designed by starting with the target emissions rate and the test parameters (draft) and the mass air flow requirement resulted in a 6in flue. Hence the King needing an 8in.

I'm exceeding the draft so my velocity and mass air flow is too high. I need the restriction to bring the mass air flow back in line yes? I'm currently doing it with a key damper but I'm thinking that causes other issues ie too low of a velocity for the the given pipe size

Like I said, there most certainly must be some sort of calculation that is run for this sort of thing. https://www.mecaflux.com/en/calculer conduit fumees.htm ?

I'm having to order 24' of flue liner so I think I'm in that range...

Draft is the pressure differential. By using a key damper you are restricting both the volume and velocity. This causes the vacume to be lessened below that damper. Going with a smaller liner increases velocity but reduces volume. This can effect different stoves in different ways. Some will actually run hotter with that increased velocity. For example regency reports their big hybrid overheating when run on a 6" chimney

 

[begreen]

Some will actually run hotter with that increased velocity. For example regency reports their big hybrid overheating when run on a 6" chimney

That happened to BrotherBart's old Sierra when he put it on a liner. I'm wondering if a better approach would be to go up to a 7 or 8" liner to slow down draft.

 

[bholler]

That happened to BrotherBart's old Sierra when he put it on a liner. I'm wondering if a better approach would be to go up to a 7 or 8" liner.

Only bk engeneers would have that answer. Different designs will react differently. That level of thermodynamics is a bit above my pay grade.

 

[black smoke signals]

Cold stove has a (look it up) t-stat adjustment measured from base to the intake flap! Sad panda my stove is still under warranty I too thought about modifying a damper or controlling the intake only thinking my stove wasn’t tested for this modification would void my warranty. Like I said at my homes high wind no burning ! modifications to the intake I would like to hear!

 

[sadpanda]

Cold stove has a (look it up) t-stat adjustment measured from base to the intake flap! Sad panda my stove is still under warranty I too thought about modifying a damper or controlling the intake only thinking my stove wasn’t tested for this modification would void my warranty. Like I said at my homes high wind no burning ! modifications to the intake I would like to hear!

I would recommend contacting BK for customer support on this issue. They stand behind their products. I 'live dangerously' and have weighed the risks of the modifications I have made... Speaking of, I am going to try a new thermostat spring as a CYA/just in case.

I am also going to get an adapter and additional length of pipe so I can reuse my old liner for now until I get this experimentation ironed out. Truthfully, I was able to heat 2k.sq ft albeit by overfiring... I am adding nearly 1k sq ft and tall ceilings, however, I am adding a ton of insulation, 100% continuous air barrier and enclosing the masonry in the building envelope... Lots of changes. If the princess can't keep up I may be looking into a hearth mounted free stander with a more generous firebox, which would require 8in liner anyway.

Is there anything pressurizing the stove room? HRV imbalance?

HA! Nothing yet. Still very drafty. House was leaky to begin with and I've been knocking down/replacing walls and building new for the past 1.5 years (long story) Hopefully we will be totally sealed up by spring and ERV will be installed then.

That happened to BrotherBart's old Sierra when he put it on a liner. I'm wondering if a better approach would be to go up to a 7 or 8" liner to slow down draft.

Playing with the engineering tool box calculators, doubling the pipe diameter did not decrease draft (pressure differential) but it did decrease velocity and increase CFM....

Only bk engeneers would have that answer. Different designs will react differently. That level of thermodynamics is a bit above my pay grade.

I agree, I'm over my head too. Maybe thats where this is all heading...



BKVP: The manuals all state that flue must AT LEAST match the diameter of the flue collar... Is there any restrictions/dangers/thoughts on going larger? I know the rules but can you at least ask the merry band of nerds if our logic is sound?