how hot can exhaust get?

I have a magnetic rutland thermostat on my 6" black stove pipe exhaust coming from my johnson energy systems j-7900 wood furnace.
I usually run exhaust temps at about 300F. Today i opened up the damper, dial damper on the front of ash pan door, and the loading door flapper was set on high. It very quickly reached 460F and set off the smoke alarm in the basement. I watched the black pipe start smoking some and stink bad. I think it was burning off some of the paint maybe.
So did i get it too hot? what temps should i be seeing on that thermostat on the black exhaust pipe?
Also ive been wondering how hot is too hot on the little dial thermodisc temp gauge that turns on the blower? My setting are 90f=off 150F=on and 200f=limit. I usually run between 100F and 160F during the day. Thanks guys

First off, it sounds like your black stove pipe is somewhat new. New stove pipe will smoke and stink something awful the first time they are exposed to higher temps. The smell and smoke is a very thin layer of oil used on the pipe from the factory to keep it from rusting, I believe. Normally, anything over 550 degrees in considered over-firing a flu, so your 470 degrees is in the normal burn zone for draft temps. As for your plenum fan temps, yours sound like they are right where they are suppose to be. Although they can be manually adjusted, I run mine in the same ballpark as yours.

yes the pipe is less than month old. Forgot to mention i now have stainless steel flue liner in the chimney if that makes a difference.

aaronmach1 said:

yes the pipe is less than month old. Forgot to mention i now have stainless steel flue liner in the chimney if that makes a difference.

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You might be getting a better draft due to the new liner and black pipe. The only time my pipe gets that hot is when I have a full load in the fire box. With the right pressure system outside I have seen mine go as high as 1000. Then I just cut down on the air intake and close down the dampner, gets it back in line then readjust from there. Some day I will be able to afford a nicer system but this one still works.

Just my 2 cents worth take it for what its worth.

Beefie

wow just realized my furnace got hot! on the thermo dial it was just past the blower limit switch at about 210F. I never had it that hot. I was throwin in small stuff as i was haulin wood in and didnt pay attention how hot it got. Did i almost over temp the furnace?

aaronmach1 said:

wow just realized my furnace got hot! on the thermo dial it was just past the blower limit switch at about 210F. I never had it that hot. I was throwin in small stuff as i was haulin wood in and didnt pay attention how hot it got. Did i almost over temp the furnace?

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Probably not, if you have a draft induced blower attached to your furnace the high limit switch would have shut it off. And the plenum fan would still be blowing to cool your furnace. According to the limit switch your unit was only about 60 degrees hotter than normal. But the actual temp of the steel and flu was probably much higher. But the furnace should be able to handle those temps. Just so you dont make a habit of letting her get that hot. Generally, smaller pieces of wood burn hot and fast. Thus raising stove temps in a hurry.

Just out of curiosity, is this a new furnace you are breaking in?

reaperman said:

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Probably not, if you have a draft induced blower attached to your furnace the high limit switch would have shut it off. And the plenum fan would still be blowing to cool your furnace. According to the limit switch your unit was only about 60 degrees hotter than normal. But the actual temp of the steel and flu was probably much higher. But the furnace should be able to handle those temps. Just so you dont make a habit of letting her get that hot. Generally, smaller pieces of wood burn hot and fast. Thus raising stove temps in a hurry.

Just out of curiosity, is this a new furnace you are breaking in?

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not a new furnace i bought it used a few weeks ago. I do not have a draft induce blower on it. Is the the only thing that the limit setting is for? Also i noticed when the furnace temp was that hot the flue temp was not much hotter if any than normal.
I just hurried up and closed flue damper and ash door dial damper untill the temps went down, i didnt know what to do.
Also is there any recomendations for my on/off blower settings. Just realized im set at Off=90F On=135F and Limit=200F. As long as i have a fire going, the blower runs all day. It only shuts off after a slow burn overnight and just coals are left in the morning.

I over-fire my furnace on a regular basis to help keep the creosote under control. I don't burn a lot of seasoned wood so burning hot helps.

I try not to let it go over 600 when I'm burning it hot. Tonight it saw 813 and I smelled it in the house. This is on a digital thermometer, mind you. I have a Rutland dial-type and it's about 70 degrees lower than what my digital is showing.

I have a wood furnace as well. My blower settings are 200 limit, 150 on, and 100 off. Stays about 130-140 during burning. A lot of that depends on the temp of return air. Mine is drawing in cold basement air as my furnace sits on the basement floor, and blows the hot air into the basement atmosphere (no ducting). From there it uses convection to heat the house. I have a constant supply of cold air running down both of my staircases into the basement.

OH_Varmntr said:

I over-fire my furnace on a regular basis to help keep the creosote under control. I don't burn a lot of seasoned wood so burning hot helps.

I try not to let it go over 600 when I'm burning it hot. Tonight it saw 813 and I smelled it in the house. This is on a digital thermometer, mind you. I have a Rutland dial-type and it's about 70 degrees lower than what my digital is showing.

I have a wood furnace as well. My blower settings are 200 limit, 150 on, and 100 off. Stays about 130-140 during burning. A lot of that depends on the temp of return air. Mine is drawing in cold basement air as my furnace sits on the basement floor, and blows the hot air into the basement atmosphere (no ducting). From there it uses convection to heat the house. I have a constant supply of cold air running down both of my staircases into the basement.

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great thanks! i assume the 600 and 800 Are flue temps???? Also how long do you let the oven over temp for?
Also now that i have a stainless steel liner is it still good to use the Rutland brand spray stuff on the fire to help get rid of creosote? Or will it hurt the liner?
Mine also draws cool basement floor air through the blower. Its not that cool though.

Yes, flue temps. I have a surface mount thermocouple attached to the flue about 4" from where it exits the firebox.

I only run it hot for about 20 minutes or so. That's at about 600. The 800+ I saw today was by accident because I wasn't paying attention. Goes to show what can happen if you get sidetracked for 10 minutes.

This will all be fixed here soon. My digital thermometer doesn't have an alarm output, but the one I'm looking at buying (~$80) does. So I'll set it to about 650 and wire up alarms on each floor so if it overfires it will sound all the alarms. I'm looking at 100db alarms so it will wake up even the heaviest sleeper (me).

As far as the creosote removing spray, I couldn't tell you if it will effect the stainless liner or not. Sorry

aaronmach1 said:

not a new furnace i bought it used a few weeks ago. I do not have a draft induce blower on it. Is the the only thing that the limit setting is for? Also i noticed when the furnace temp was that hot the flue temp was not much hotter if any than normal.
I just hurried up and closed flue damper and ash door dial damper untill the temps went down, i didnt know what to do.
Also is there any recomendations for my on/off blower settings. Just realized im set at Off=90F On=135F and Limit=200F. As long as i have a fire going, the blower runs all day. It only shuts off after a slow burn overnight and just coals are left in the morning.

Click to expand...

The limit switch control tow things. First, it controls at what temp the plenum fan turns on at. On your unit it turn the fan on at 135 and off at 90. The high limit part of the switch (200 on your unit) will shut off the draft blower because at that temp the furnace doesnt need any more forced air. Plus 200 is getting plenty hot.

thanks alot guys this was very helpfull!

OH_Varmntr said:

This will all be fixed here soon. My digital thermometer doesn't have an alarm output, but the one I'm looking at buying (~$80) does. So I'll set it to about 650 and wire up alarms on each floor so if it overfires it will sound all the alarms. I'm looking at 100db alarms so it will wake up even the heaviest sleeper (me).

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Do you have a link of where to buy this type of alarm thermometer?

aaronmach1 said:

Do you have a link of where to buy this type of alarm thermometer?

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Here is the one I'm looking to buy. The only thing is that it is powered by 12VDC because it is an automotive unit, so you'll have to find a 110VAC to 12VDC transformer to power the unit. If you do some research you can find an AC powered unit.

Digital EGT Thermometer/Pyrometer with analog output [SYL-1812RA] - $78.50 : auberins.com, Temperature control solutions for home and industry

It has an analog output for the alarm, which I am going to wire up the alarms so they serve 2 functions. For one, they will sound when the high alarm sounds. I will also wire up a set of alarms that will sound if we lose power at the house. These will be wired up to a relay that holds the contacts open, and if we lose power, the contacts will close and connect the alarms to a battery which I will have on a battery tender. That way if the power goes out during the night while we're sleeping, we can wake up and set the furnace up to run with no power, or fire up a generator (on my list of things to buy).

The thermocouple I am using is a type-k surface mount thermocouple. Hold onto your britches, those fellas are expensive.

I found this one as well, and this is actually what I have on my furnace now, but mine lacks alarm outputs.

http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=106&zenid=c4c435bd2f7c2ba24d5bd79ccb9e8600

This one can be powered by 110VAC, but it is a PID temp controller used to control the process temperatures of an oven or the like. It has heat/cool outputs that are used to control process temps and it will constantly try to control the temp and you'll constantly hear it click as it tries to control it. As long as the outputs aren't hooked up to anything you'll be fine.

Both units can use the same type of thermocouple.

You can see my unit resting on the air makeup box of my furnace. When I get the right one I want I'll mount it on the wall.

OH_Varmntr said:

Here is the one I'm looking to buy. The only thing is that it is powered by 12VDC because it is an automotive unit, so you'll have to find a 110VAC to 12VDC transformer to power the unit. If you do some research you can find an AC powered unit.

Digital EGT Thermometer/Pyrometer with analog output [SYL-1812RA] - $78.50 : auberins.com, Temperature control solutions for home and industry

It has an analog output for the alarm, which I am going to wire up the alarms so they serve 2 functions. For one, they will sound when the high alarm sounds. I will also wire up a set of alarms that will sound if we lose power at the house. These will be wired up to a relay that holds the contacts open, and if we lose power, the contacts will close and connect the alarms to a battery which I will have on a battery tender. That way if the power goes out during the night while we're sleeping, we can wake up and set the furnace up to run with no power, or fire up a generator (on my list of things to buy).

The thermocouple I am using is a type-k surface mount thermocouple. Hold onto your britches, those fellas are expensive.

Click to expand...

Do you just leave a multi meter hooked up to the k-type t/c? how is the t/c attached to the pipe? I work with k-type t/c's all the time.

aaronmach1 said:

Do you have a link of where to buy this type of alarm thermometer?

Click to expand...

I found a kit already put together on ebay, it looks like a good idea

Woodstove stove pipe Alarm Thermometer flue temp wood | eBay

OMG.....OMG.....OMG!!!!!

What the hell are you guys doing?????
If I am wrong..my bad ,but it looks like you are taking external pipe temps?

If so add 400-500 degrees. To make an accurate measurement you must take it from the center of the flue.

...to add you are advocating over firing...most warranties are now void due to that advice.

CrappieKeith said:

OMG.....OMG.....OMG!!!!!

What the hell are you guys doing?????
If I am wrong..my bad ,but it looks like you are taking external pipe temps?

If so add 400-500 degrees. To make an accurate measurement you must take it from the center of the flue.

...to add you are advocating over firing...most warranties are now void due to that advice.

Click to expand...

are you telling me that when my magnetic rutland thermometer on the exhaust 6" stove pipe to chimney says 400 that im actually at 800 or 900F ? My normal burns usually read at 200 to 300F on that thermo.

aaronmach1 said:

are you telling me that when my magnetic rutland thermometer on the exhaust 6" stove pipe to chimney says 400 that im actually at 800 or 900F ? My normal burns usually read at 200 to 300F on that thermo.

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That's what I'm telling you if your therm. is out side the pipe.
At 200 you should have buckets of liquid pouring out your pipe. If you do not it is hotter than 200 and at 300 you'll have some creosote build up.

CrappieKeith said:

That's what I'm telling you if your therm. is out side the pipe.
At 200 you should have buckets of liquid pouring out your pipe. If you do not it is hotter than 200 and at 300 you'll have some creosote build up.

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holy balls. i had it at 450 the otherday according to magnet thermo on the pipe.(according to you it was more like 900F.) If these are that far off how the hell can they sell them? it even says "burn range" from like 300-500F. Overfire at like 600-900F and 100-300 says creosote.