New Princess 29 Insert - Questions - Running Very Hot & Installation

[fallingpines]

Block off plates are not common with stove installers at all. It is not required by code at all so they don't do it. But it really does make a big difference. The furnace cement it far from permanent it will crack and crumble away shortly

They got the green light from BK to use mill-pac (actually got permission right after initially coating everything with furnace cement), so I'm guessing that will be the approach in the future.

I'd honestly like to see a 15 used in there so it seats a bit better, but they were limited at the time to what was supplied, the 30. That is a bit unfortunate.

I snapped a few pictures of what I have going on above the unit now. They wanted to make sure it was not going to leak, but I'm not sure if less is more in these cases. haha.

You can see the original damper which was removed however many years ago and served as the hanging point for the old barely insulated block off plate from the country comfort. It was actually only held up by two metal pipes behind the stove and optimistic gravity. With how leaky and poorly installed it was, it served very little purpose now so it was discarded.

Before anyone asks why I didn't install myself and do things like the 15 angle and block off plate, to get the tax credits and insurance blessing it needed to be installed by a certified professional team.

 

[BKVP]

Then I don't understand the following earlier remark:
"The old chimney had the block off plate directly above the unit about 2 feet above which opened into the ceramic."

All I'm saying is that a cold air falling down the chimney is bound to open the Tstat, leading to shorter, more intense burns (and possibly heat disappearing up the flue outside of the liner). Hence a block off plate where the liner enters the chimney is a good thing to do.

The thermostat would not be effected a cold downward draft in the PI29. It's front of shroud and right of loading door.

 

[begreen]

Good at least that they used the right adapter elbow for flex. They sure goobered on the milpac. It doesn't look like it is sealing anything and shouldn't be necessary at all for the elbow to flex connection.

 

[BKVP]

Burn away! You'll find the cat will calm down..probably bit by bit. Most notably will be next season. Good job!

 

[fallingpines]

Unfortunately, there are still issues with the unit. It seems the thermostat/bimetal coil is having some major issues controlling the damper. I would expect it to slowly close as the unit heats up and approaches the overfiring temp. Looking into the side when the surface temps are over 600 (cat temps are past the active zone), the damper remains open with plenty of travel left before closing. I found the only way to control things is to turn it down to below the halfway point. This matches with what I saw when it reached 768 from a few nights back. (damper was not anywhere near closing)

I know the scale of the thermostat is generic and different for each stove based on the conditions present, but I'm using it to describe the issues seen. So that others have an idea of the scale, it is Low - 8 equally spaced dots - High

Instead of having the full range of the thermostat, I've found it dies out at "low" and it runs away at anything above dot 5. When I put it at about 4.5 it will remain near the top of the active cat zone and surface stays between 500 and 600. (How I would expect high to function).
If I set it at the second dot it barely stays in the active zone. (How I would roughly expect Low to function)
So there is very little control available from the installed thermostat. 2-3, 3-4, 4-5.

I fired it up this weekend and waited till things got nice and hot, swapped over to the cat and waited for it to stabilize at High, the heat just continued to rise up with surface temps climbing past 600 and getting back up to 700...again. (Verified by infrared and the surface thermometer). I looked through the side grate to see the damper flap still open by about an inch. Turning thermostat down, it only closed below the 5th dot. I'm wondering just how hot things would need to get for it to actually close.

I then left it at 4.5 and waited to see how things stabilized. When the temps lowered, the damper very slowly opened and closed, keeping the unit operating at the top of the active range for the temperature probe. So the automated adjustment works to some extent.

Later I turned it down to Low and noticed that it cooled down to below the active zone (damper flap stayed closed until it was below active), so I went to between dot 2 and 3. This kept the temp probe at about 1/5 into the active zone and stove temps above 450 though I need to test again with the infrared thermometer.

With all that information to work with and ruling out the other issues from before (since the installer team worked through them), there is an issue with this thermostat. Without taking it apart, I'm not sure if it is an adjustment issue or a problem with the bimetal coil. My guess is the bimetal coil since the actual scale between Low and High is half what it should be. Repositioning the coil unit or lengthening the chain would simply make the flap remain closed until the thermostat was raised even further than 2, (so we would just make 6 the new Low and it would max at High) again..this points to the coil. This could be a one-off issue with the supplier of the coils, as we have had two years of supply chain disruption. Looking back into the forums I see years ago others had issues with the coils from day 1 and a replacement resolved things. They had a positive feedback loop active for some reason, luckily mine is a negative feedback loop but the scale is off from where it should be.

 

[stoveliker]

The thermostat is not meant to control the cat gauge. It is meant to control the overall temperature of the stove.

I would not worry about the cat gauge overactive; in fact, having too much air would result in a *lower* cat temperature because it will see less fuel (smoke) because the air allows it to be burned in the firebox before it reaches the cat.

The cat gauge is *not* an indicator or overfiring. At all.

It is also common to not be able to run at the lowest Tstat setting as it depends on your draft. Each system has a different lowest operable setting.

 

[fallingpines]

The thermostat is not meant to control the cat gauge. It is meant to control the overall temperature of the stove.

I would not worry about the cat gauge overactive; in fact, having too much air would result in a *lower* cat temperature because it will see less fuel (smoke) because the air allows it to be burned in the firebox before it reaches the cat.

The cat gauge is *not* an indicator or overfiring. At all.

It is also common to not be able to run at the lowest Tstat setting as it depends on your draft. Each system has a different lowest operable setting.

The thermostat is meant sit on the side of the stove and the coil winds/unwinds (depending on design, which metal is on the inside or outside) as the temperature goes up it lowers the flap on the damper to bring the temps down by controlling the airflow into the unit. I get how those work.

You'll notice I mentioned the surface temperatures of the stove. (blower off and stabilized before measuring) Even speaking with the installers, they said that the temperatures I was able to send them pictures of was dangerous and the video of the unit smoking off the paint was not what should be occurring.

I've accepted that the cat temps will settle down over time, but if the unit is not closing the damper as it should at high temps, there is a problem.

 

[stoveliker]

The thermostat is meant sit on the side of the stove and the coil winds/unwinds (depending on design, which metal is on the inside or outside) as the temperature goes up it lowers the flap on the damper to bring the temps down by controlling the airflow into the unit. I get how those work.

You'll notice I mentioned the surface temperatures of the stove. (blower off and stabilized before measuring) Even speaking with the installers, they said that the temperatures I was able to send them pictures of was dangerous and the video of the unit smoking off the paint was not what should be occurring.

I've accepted that the cat temps will settle down over time, but if the unit is not closing the damper as it should at high temps, there is a problem.

I am sorry, but I see no indication of overfiring. 700 surface temp is not overfiring.
You relate the cat gauge indication to the action of the thermostat. These are *not* directly (in first order) related. Closing down the thermostat could increase the cat gauge, and that is perfectly normal.
The thermostat manages the air based on the output temperature of the stove, which is a combination of the heat output of the firebox and the heat output of the cat. So looking at only the cat gauge to correlate with the Tstat action is not the right way of thinking.

So I see no indication of overfiring, I explained that the low end of the workable range is *often* not the low end of the thermostat range (i.e. if you have a short chimney, less draft, the lowest workable Tstat setting might be at 2.30 or so because below that you'd not have enough draft to suck in enough air to keep the burn going).

The unit smoking off the paint is normal for a new unit, and will happen each time you reach a higher temperature than before.

Edit: there could of course be something wrong with the Tstat, but I see no indication of that being the case in your description.

 

[stoveliker]

I fired it up this weekend and waited till things got nice and hot, swapped over to the cat and waited for it to stabilize at High, the heat just continued to rise up with surface temps climbing past 600 and getting back up to 700...again. (Verified by infrared and the surface thermometer). I looked through the side grate to see the damper flap still open by about an inch.

This just indicates that the setting on the thermostat you had here was simply a higher heat output than you expected or wished.

The thermostat has very precise control in a certain range. In particular between 2 and 4, very small changes (fractions of the distance between your dots) will have significant consequences.

 

[fallingpines]

This just indicates that the setting on the thermostat you had here was simply a higher heat output than you expected or wished.

The thermostat has very precise control in a certain range. In particular between 2 and 4, very small changes (fractions of the distance between your dots) will have significant consequences.

Sorry, but that's not correct at all. That's like saying the thermostat in your house only works between 70-74 and if you set it to 75 and the temperature goes to 95 its just a higher heat output than you expected or wished.

These coils are not new technology, they are how thermostats have been controlled for years prior to the digital ones being used today. This is a heavier duty unit than what was found in a normal house thermostat. There is a science behind them and they can be tuned for a range of temperatures based on material expansion coefficients of the metals used. It has been mentioned many times on this forum that the BK units will self regulate and prevent themselves from getting too hot, even at a High setting. However, that is only if the bimetal coil is operating as intended and has been tuned properly. It's why they don't want the consumer to mess with it and why I haven't opened up the unit to see what is going on. The selling point of these units is how they are safe and they auto regulate using this technology.

 

[stoveliker]

I know how they work; I have a master's in materials science and a PhD in physics.

It appears you know how these units run despite this being your start in the game.

I am only telling you what people experience. Almost no one can run at the lowest setting of the Tstat. Why? Because the setting does not independently control the air, it is dependent on the engine that sucks the air in, your draft. That differs for each system..it can only alter that given (based on chimney, weather and a host of other parameters not influenceable by the Tstat) suction power by constricting the flow.

It is not calibrated to the measurement of your cat gauge. The measurements of your cat gauge doesn't give the heat output of the system. It is only telling you when to close the bypass. Period.

And I have not seen evidence presented that your unit overfires.

 

[BKVP]

OP, please call 509-522-2730 tomorrow and ask for Francisco. He will help you. He'll need the name of the dealer.