Dwyer Magnehelic Install

michaelanthony · Post by **michaelanthony** » Mon. Nov. 16, 2015 5:15 am

hotblast1357 wrote:sounds perfect, you don't want it below -.005 or above -.05.

...agree^^^sounds good, looks good! You said a mouthful in your thermometer thread in regards to internal flue pipe temps, I am curious to hear your flue pipe temps during various stages of fire. Your observation has me considering an internal thermometer as well.

Smokeyja · Post by **Smokeyja** » Mon. Nov. 16, 2015 7:19 am

michaelanthony wrote:
hotblast1357 wrote:sounds perfect, you don't want it below -.005 or above -.05.
...agree^^^sounds good, looks good! You said a mouthful in your thermometer thread in regards to internal flue pipe temps, I am curious to hear your flue pipe temps during various stages of fire. Your observation has me considering an internal thermometer as well.

Well I thought it would be a lot closer to the surface temp . But the mistake I made was ever trusting these magnetic thermometers . I knew there was a difference in internal temps but not the poor mechanics of the mag thermometers .

I'll post more in the thermometer thread but I will say the thermocouple in the flu peaked over 1000°F while getting the wood fire going while the surface thermometer didn't budge over 200° .

Sunny Boy · Post by **Sunny Boy** » Mon. Nov. 16, 2015 8:54 am

Smokeyja wrote:
michaelanthony wrote:
...agree^^^sounds good, looks good! You said a mouthful in your thermometer thread in regards to internal flue pipe temps, I am curious to hear your flue pipe temps during various stages of fire. Your observation has me considering an internal thermometer as well.
Well I thought it would be a lot closer to the surface temp . But the mistake I made was ever trusting these magnetic thermometers . I knew there was a difference in internal temps but not the poor mechanics of the mag thermometers .

I'll post more in the thermometer thread but I will say the thermocouple in the flu peaked over 1000°F while getting the wood fire going while the surface thermometer didn't budge over 200° .

If you were to use a hand-held, long probe type K thermocouple, you'd also see a pretty good range of temps inside the pipe. Hottest being nearest to the center of the pipe where the inner most gas stream is insulated by the outer layer of gases and is not losing heat to the pipe.

And it varies where along the length of the pipe, too. Flow turbulence around bends and past an MPDs can cause the hottest stream of gases to shift away from the pipe center. Using an IR gun you can see different parts of the pipe are hotter and it doesn't always relate to distance from the stove collar.

Paul

ddahlgren · Post by **ddahlgren** » Mon. Nov. 16, 2015 10:32 am

I have used a probe since wood burning days and ignore magnetic ones entirely as just stove trinkets at best. I never got to the burn zone with magnetic yet never had any creosote either as always ran with probe in the 300 to 400 range well out of harms way. Surface to probe I have found to be a bit over 2X more on probe 180 surface close to 400 probe typical.

Smokeyja · Post by **Smokeyja** » Mon. Nov. 16, 2015 1:15 pm

Sunny Boy wrote:
If you were to use a hand-held, long probe type K thermocouple, you'd also see a pretty good range of temps inside the pipe. Hottest being nearest to the center of the pipe where the inner most gas stream is insulated by the outer layer of gases and is not losing heat to the pipe.

And it varies where along the length of the pipe, too. Flow turbulence around bends and past an MPDs can cause the hottest stream of gases to shift away from the pipe center. Using an IR gun you can see different parts of the pipe are hotter and it doesn't always relate to distance from the stove collar.

Paul

Paul I am using K type thermocouples so I am seeing that range you are talking about . Check out the thermometer thread on the hardware I purchased and installed . And I already notice a slight difference with the Mercury filled gauge which uses a large bulb probe right in the upper 90° bend . It's about 30° F cooler just in that short distance . I am also using a K type thermocouple probe in the firepot .

It's fun to watch the Magnehelic move upwards with the temp going up . I just think this is all amazing to watch .

Smokeyja · Post by **Smokeyja** » Mon. Nov. 16, 2015 1:16 pm

ddahlgren wrote:I have used a probe since wood burning days and ignore magnetic ones entirely as just stove trinkets at best. I never got to the burn zone with magnetic yet never had any creosote either as always ran with probe in the 300 to 400 range well out of harms way. Surface to probe I have found to be a bit over 2X more on probe 180 surface close to 400 probe typical.

I wish I had done this from the beginning . I'm not sure why I wasted my time and money on anything else to this point .

ddahlgren · Post by **ddahlgren** » Mon. Nov. 16, 2015 2:01 pm

Smokeyja wrote:
ddahlgren wrote:I have used a probe since wood burning days and ignore magnetic ones entirely as just stove trinkets at best. I never got to the burn zone with magnetic yet never had any creosote either as always ran with probe in the 300 to 400 range well out of harms way. Surface to probe I have found to be a bit over 2X more on probe 180 surface close to 400 probe typical.
I wish I had done this from the beginning . I'm not sure why I wasted my time and money on anything else to this point .

I think the largest problem is putting a flat thermometer on a round pipe lets room air cool off the thermometer.

Sunny Boy · Post by **Sunny Boy** » Mon. Nov. 16, 2015 2:17 pm

ddahlgren wrote:
Smokeyja wrote:
I wish I had done this from the beginning . I'm not sure why I wasted my time and money on anything else to this point .
I think the largest problem is putting a flat thermometer on a round pipe lets room air cool off the thermometer.

That's why mines on a vertical section, not horizontal. There was too much difference in IR gun reading and magnetic gauge reading. Moved it to a vertical section on the stove side and just a few feet above the stove collar and it reads the same surface temps as the IR gun reads on the pipe surface next to it.

Works well for seeing what the stove is doing at a glance, without always having to pick up the I R gun.

Not sure all the Rutland magnetic are this accurate. And I'm amazed it's stayed this accurate for 10 years now. Often bi-metallic types loose some range with use and years. I've got other bi-metaling gauges and most were only good for paper weights !

Paul

Smokeyja · Post by **Smokeyja** » Mon. Nov. 16, 2015 2:22 pm

Sunny Boy wrote:
That's why mines on a vertical section, not horizontal. There was too much difference in IR gun reading and magnetic gauge reading. Moved it to a vertical section on the stove side and just a few feet above the stove collar and it reads the same surface temps as the IR gun reads on the pipe surface next to it.

Works well for seeing what the stove is doing at a glance, without always having to pick up the I R gun.

Not sure all the Rutland magnetic are this accurate. And I'm amazed it's stayed this accurate for 10 years now. Often bi-metallic types loose some range with use and years. I've got other bi-metaling gauges and most were only good for paper weights !

Paul

My newest Rutlands one is 100% crap . The older ones I bought a few years back have gotten me through all the other winters burning with good results ,although still inaccurate, at least it was a consistent inaccuracy .

If anything I really didn't need the Magnehelic gauge to figure anything out . It's just neat to watch . My wife said now instead of a classy rustic look I went for the mad scientist look.

Haha

ddahlgren · Post by **ddahlgren** » Mon. Nov. 16, 2015 2:30 pm

Vertical or horizontal makes no difference the pipe round the magnet flat.

Sunny Boy · Post by **Sunny Boy** » Mon. Nov. 16, 2015 3:31 pm

ddahlgren wrote:Vertical or horizontal makes no difference the pipe round the magnet flat.

Sure,....... but, only if you ignore convection currents and the heat coming off the longer length of vertical pipe below the magnetic gauge that is pre-heating the air before it gets to the gauge.

Here you can see my IR gun is reading 115F. And the magnetic gauge needle is reading above 100F, just shy of a being a quarter of the way to 200F - close to where 115F would be if the gauge had a scale with more divisions.

Paul

Dwyer Magnehelic Install

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