Thoughts on this Flue Temp Sensor

[fao1989]

Fellow Woodburners:

Happy with my BK A25. Installed in masonry/brick fireplace.
Considering a Magnetic sensor on liner or insert top, behind the cover, near the collar.

Attracted to the idea that this type might avoid me having to pull out blocker plate (already installed) or drill into the flue liner.
The video and sales page claim the connection is good to 800 C, which is clearly sufficient for the application.

Interested in your Thoughts.

video:

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Source page: https://tempsure.net/product/tempsure-wifi-module-kit/

Thanks!

 

[begreen]

I wouldn't cut or drill into the flex liner, especially if it is a thin one.

 

[fao1989]

I wouldn't cut or drill into the flex liner, especially if it is a thin one.

Thank you begreen. Concur.

That's what drew me to the idea of a magnetic probe that i might be able to place on the insert neat the collar somewhere, but behind the decorative A25 fireplace surround. Wouldn't be as instantaneous or accurate as a flue gas monitor, but would give a fair reading of the top temps near the exit point near the collar.

 

[begreen]

Yes, that's a better plan. Does the flue collar have a neck that it could attach to? If not, the stove top, maybe switch to a probe that is compatible and attach that through the appliance adapter?

 

[fao1989]

The A25 manual shows a flue collar neck that looks like it might be a good spot. If I can get my hand around there, i might be able to get a good attachment for the magnet at/near the collar assembly. And would avoid moving the insert or altering any of the installation or piercing anything.

The other concern is pulling the K type probe wire between the metal surround shroud and the fireplace brick edge to get the probe connector to the battery powered monitor/display, outside the shroud. I need to do that without subjecting the cable to minor risk of rub-wear over time. I'd need to protect that thin cord with some kind of very thin wedge or metal shim to sustain a small crevice at the bottom shroud edge. Im thinking maybe a metal washer?

What did you mean by: "attach that through the appliance adapter"?

 

[begreen]

The appliance adapter is what connects the liner to the flue collar.

 

[fao1989]

The appliance adapter is what connects the liner to the flue collar.

View attachment 333132 View attachment 333133

Ah.
So thread a probe between, or pierce this connector?

My instinct is to use the magnet connector on the collar and accept the delay/difference in temps from the outside option.

 

[begreen]

It could have a thermocouple washer held captive by the band clamp or an 1/8" hole drilled into the adapter for a 4" probe.

 

[fao1989]

It could have a thermocouple washer held captive by the band clamp or an 1/8" hole drilled into the adapter for a 4" probe

Great options. Presume if I used a 4 in probe, I'd have to pull it out each year for an annual cleaning.

 

[fao1989]

Great options. Presume if I used a 4 in probe, I'd have to pull it out each year for an annual cleaning.

Update and request for opinions:

You may recall, I was following discussions here of flue temps and was looking for an approach for my A25 insert.
Ultimately I used an Auber 200 connected to a K-type thermocouple washer probe (rated to 1650F).
When we cleaned the liner, I had my dealer/installer connect the sensor to the outside of the stove collar at the front to the collar with a screw to the collar (see image, location at end of red arrow). The probe connects to the Auber with the Auber OEM cable (rated to 900F), not touching the stove directly. [Bonus: after about a cord or so of burning 20% MC: negligible creosote; nearly none when cleaning].

I chose this approach instead of a penetrating probe because I both didn't want to pierce the stainless steel flue liner, nor have to pull the Ashford25 out of the fireplace and remove the probe every time I clean it.

Following the discussions I recognize that although I now have measurements of the OUTSIDE collar temps, these are lower than the actual interior liner temps. So accepting this fact, and recognizing that the outside temp is only a proxy for inside liner temps, I should probably double the Auber temp to get to a closer approximation of whats going on inside the liner.

I measured last night, shortly after start up, full load of all white oak, small splits, MC ~15-18%, with by-pass closed. Fully and vigorously burning and cat active, thermostat at about 75-80% of WOT, for about 5-8 minutes. I got a reading of 480F from the sensor on outside of that collar, before I dialed it back to to lowest setting. My logic? Keep the inside liner temps under 1000F, if the outside is approaching 500F.

Also rechecked my chimney height today, which I now believe is ~24-25 ft [I am essentially at sea level]. I do know my draft is strong and is positive before I light the fire. Never had any smoke puff back into the living room, when lighting. Ever.

So, some thoughts and looking for some opinions.

- Should I assume the measured collar temp is roughly one-half of inside liner temp? Or is the collar so close to the cat that the outside sensor at the collar is over-representing/inflating the inside liner temps?
- How high can I safely let the measured collar temp rise to, if it is in fact, one half of the inside temp? Put another way, if the collar connects to the first part of the liner, how hot can that get? My dealer said stainless steel liners are rated to 2000F. But recalling reading on this forum, not to exceed 1000F for the liners. Yes?

Normally, I run the A25 insert low and slow. Last night after the run up and then throttling down, I ran it from 30% to throttled completely back. The Auber readings from 400F down to 280F while cat still in active range, before we turned in. It went about 12 hours with coals in the morning.

- Can I ever run this insert on WOT for any length of time without worry? Am I being too conservative and over-analyzing ? Never quite get it hot enough to burn off the glass corner angel wings.

Thoughts?

Thank you!

 

[EbS-P]

I bet if drilled a hole a used the probe you’d see flue gas’s at that location is not double. I use a similar setup. Washer k type shoved up under the liner insulation 4” above the connector. I think my alarm is set at 650. I have not confirmed with my probe but I want to switch because the probe reacts so much faster.

 

[begreen]

Agreed, my thought was that the surface temp that close to the flue collar would be different, though how much is just a guess. Maybe the flue gas temp is 1.5 times the surface temp at that location?

 

[fao1989]

I bet if drilled a hole a used the probe you’d see flue gas’s at that location is not double. I use a similar setup. Washer k type shoved up under the liner insulation 4” above the connector. I think my alarm is set at 650. I have not confirmed with my probe but I want to switch because the probe reacts so much faster.

EbS-P: Thanks for the response. If your sensor is currently attached outside the liner, and your alarm is set to 650 - what is your comfort level for limit of likely inside temp? 750? 800? 1000? What do you think the highest run temp "should" be?

 

[fao1989]

Agreed, my thought was that the surface temp that close to the flue collar would be different, though how much is just a guess. Maybe the flue gas temp is 1.5 times the surface temp at that location?

Thanks begreen. I *thought* I'd seen a few threads that said, "double" any outside temperature for an inside approximation. With a draft of 24ish feet, I'm reluctant to run WOT for concern of it taking off and rising uncontrollably. Although I'd heard that Blaze Kings will shut the throttle before that?

 

[BKVP]

Agreed, my thought was that the surface temp that close to the flue collar would be different, though how much is just a guess. Maybe the flue gas temp is 1.5 times the surface temp at that location?

Depends on if the bypass is in open or closed position.

BKVP

 

[fao1989]

Depends on if the bypass is in open or closed position.

BKVP

In my case the bypass is closed, when the cat indicator lit [in red zone] and outside collar temp then reading about 300F. With throttle at ~80% on my A25, I let it run 5-8 mins before outside collar temps reached about 480F before I then throttled back. Noting that my chimney height is about 24-25 feet.

BKVP, absent an inside liner sensor, what do you estimate the actual insider liner temp is with bypass closed compared to the collar? Twice as high? Half again as high? When is a SS liner getting 'too hot'?

I'm trying to consider if the taller chimney height should influence my approach to running WOT for any length of time? Like to clean the glass.

Thank you!

 

[EbS-P]

EbS-P: Thanks for the response. If your sensor is currently attached outside the liner, and your alarm is set to 650 - what is your comfort level for limit of likely inside temp? 750? 800? 1000? What do you think the highest run temp "should" be?

The real question is i don’t know because I haven’t looked. Nothing has ever glowed. Temper colors say I’m ok. Stove top temps don’t exceed 700. Like I said buy a probe and drill a hole and use the actual data to calibrate your own setup.

I’m guessing based on my insert flue gas measurements that you are probably just fine. My probe alarm on my insert with 23’ of insulated liner is 950. It has a damper in the adapter and the probe touches the damper. It regularly sees 950. Nothing glows. It won’t burn below 600F.

My hunch is that in the first 18” of flue the temps drop quite a bit. The radiant heat from the stove keeps the surface temps of all pipes much higher than 1/2 the flue gas temps.

 

[fao1989]

In my case the bypass is closed, when the cat indicator lit [in red zone] and outside collar temp then reading about 300F. With throttle at ~80% on my A25, I let it run 5-8 mins before outside collar temps reached about 480F before I then throttled back. Noting that my chimney height is about 24-25 feet.

BKVP, absent an inside liner sensor, what do you estimate the actual insider liner temp is with bypass closed compared to the collar? Twice as high? Half again as high? When is a SS liner getting 'too hot'?

I'm trying to consider if the taller chimney height should influence my approach to running WOT for any length of time? Like to clean the glass.

Thank you!

I should say I closed the bypass when when the cat indicator lit [in red zone] and outside collar temp were then reading about 300F. Temps then rose to 480F before I throttled back.

 

[BKVP]

There are too many geeks these days. The actual flue collar is downstream of the combustor. What is expected flue collar temp in relation to flue gas temps? Is the cat 600F or 1,400F? There are several influences on temperatures, far too many to make a steadfast assertion.

I know liners can take much higher themselves you'll generate from a properly installed and properly operated wood stove.

BKVP

 

[EbS-P]

There are too many geeks these days.

I’m offended I went to school for way too many years and earned that badge!

 

[begreen]

The contradiction here is the difference between true cat stove and tube secondary stove flue temps.

 

[BKVP]

I’m offended I went to school for way too many years and earned that badge!

And they divulge who they are!

 

[RustyShackleford]

Did someone say geek ? I'll bet I'm not the only person here who's imagined hooking a stepper motor to the intake flapper, plus a bunch of thermistors and thermocouples in various locations, and hooking it all up to an Arduino !

 

[BKVP]

Did someone say geek ? I'll bet I'm not the only person here who's imagined hooking a stepper motor to the intake flapper, plus a bunch of thermistors and thermocouples in various locations, and hooking it all up to an Arduino !

Webster's Dictionary defines Geek as:
One who's imagined hooking a stepper motor to the intake flapper, plus a bunch of thermistors and thermocouples in various locations, and hooking it all up to an Arduino !

BKVP

 

[stoveliker]

A real geek would measure before calibrating a derived quantity (collar temp), or before starting to design active elements in a system...