Update on the Stovetop Versus Over the Door Temperature Experiment

[BrotherBart]

Back before the season started I posted a thread about an experiment I did with my old insert out in the East 40. In a nutshell I burned the dickens out of it with continuous loading of dry cardboard. In the first place to dispose of a huge bunch of cardboard I needed to get rid of without filling up the landfill and secondly to determine if people that measure their insert stove temps with thermometers over the door were getting accurate information.

The results of the outdoor test were that the front of the stove body consistently was 100 degrees less than the temperature of the top plate of the stove measured centered halfway between the flue collar and the front lip of the top plate. Since the insert being used was a pre-EPA beast a legitimate question was raised whether this result would be consistent with the same test done with an EPA re-burn insert since the hot flue gases of the EPA unit are blown toward the front of the stove and they smack into the front of the stove prior to exiting over the front of the baffle. Well the results are in.

For the last three nights I have made the same observations using my Englander 30. The same construction as a standard tube type reburn EPA insert. And at every stage of the burn from 300 degrees stove top temp on up the temperature measurements on the front of the stove above the door was almost exactly 100 degrees less than the temperature of the top plate measured centered on the lower step of the top.

This is just for information purposes and because I like to play with wood stoves. Others are encouraged to verify the results as true on other stoves or as the biggest crock of it since Bub suggested burning green wood.

 

[Backwoods Savage]

Didn't your mother tell you to stop playing with fire BB?

 

[gzecc]

BB that was great timing. I just asked that question. I assumed as much but now have the case study.

 

[woodconvert]

I don't have an insert but on my stove if I put the thermometer on the door OR the top right front of the top surface of the stove I get the same temps. If I move it to the center of the top surface (on my top loading door) it's measures about 150-200 higher.

 

[fullbore]

My Quad is about 150* warmer on the stove top than the front door. Normally 750* vs. 600*

 

[Rockey]

Oddly enough i was just thinking about this last night. Good information. Did you have the blower running on the 30 when you took these readings? I'm assuming your insert did not have a fan running at the time it was being tested. Almost all inserts have the fan running which would keep the top much cooler and make the correlation between stove top and door a bit closer. Just food for thought.

 

[BrotherBart]

Oddly enough i was just thinking about this last night. Good information. Did you have the blower running on the 30 when you took these readings? I'm assuming your insert did not have a fan running at the time it was being tested. Almost all inserts have the fan running which would keep the top much cooler and make the correlation between stove top and door a bit closer. Just food for thought.

The blower wasn't running on either one during the comparison.

 

[Hogwildz]

Thanks for the results Bart.
I really don't rely on the thermo much anymore. I use it as at 200 on mine its going to be longer restart of reload then if I reload at 300 or above.
At high end its usually about 700-750 at initial reload spike, then cruises around 650. I can cut the air back at 400 or 500 and it still works its way up to 700ish then settles back down at 650ish.
There is only so much control on a stove, and I know after 3 years burning mine, that she likes to run at 650, no matter what I do, unless I run small loads. Thats the sweet spot, nothing glows and she runs there for the majority of the burn. I gave up trying to hold the reigns tightly a long time ago. I let her run, or should say she runs where she likes to and have had no ill effects as of yet, thank goodness.
Now before I adjusted the door the first year, and the thermo was pegged the first few fires, that made me worry.

I will say I neglected to cut the air back till she was about 650-700 today, she ran for a bit longer at 750 and the house rose 1 degree warmer then the steady 75 she ran all day. At 76, a whole 1 degree warmer, the wood lasted a noticeably shorter time and for only a 1 degree rise. So in essence, at least for me, trying to burn flat out, any higher than she usually cruises at, is not worth the 1 degree rise at a considerably shorter burn time.
I pretty much have it set that at 650, I get the most beneficial burn times & heat production. Anything more is like going over 55 on the highway and burning more gas. Yes at lower I can get longer burn times, but at a less efficient burn, and at a lower house temp held. Load it, let it flame, close it back, let her cruise at the temp she likes to cruise at, for me there is not better temp or burn time for ratio of wood consumed vs. heat output and steady house temp.

One other note:
I can only speak for the Summit. as that is what I have fired. The baffle design puts the majority of the secondary out the front, which is blasting right at the front of the stove, and actually just about at thermo level.
When I get some free time, I will conduct a similar test. But I strongly believe the way the Summit is set up, the temp on the front with the majority of the secondary blasting at the front, is giving a fairly accurate real world temp.
If I ever get to test my theory, I will post results.

 

[Superlite]

More of a question from me,

I keep my thermometer on the flue pipe right where it goes into the terracotta pipe, actually right on the outside of the 90 that goes into the terracotta. I was always under the impression that the temp should be taken at the flue and not the stove top. Does it matter? Or should I have one for both? Does anyone else keep theirs on the flue?
Thanks

edit: I understand this thread is about inserts, but I have read a lot about stove top temp on here lately, and I was wondering what other people do...

 

[BrotherBart]

On my stoves that aren't sitting inside of a fireplace I have thermos on the pipe and the stove top. I would love to have one on the pipe for the one in the fireplace but it won't work.

 

[RedRanger]

Well now I am really stumped!! I have my thermomoter on the top of the insert and never get it past 500F. But there is plenty of heat, so much that if my face is at that spot where the blower is shooting the hot air out,, it damn near feels like a "burn"..

Could the air from the blower passing over the thermomoter be cooling the reading?

Guess I could try a door reading, and a top reading without the blower running. Thing is, it`s so damn cold around here right now that I am keeping that blower running from mid to high non-stop.

Here is why I am puzzled? With the old non-epa insert I could only place the therm on the door and got readings of 450F consistently. But that insert did not produce near the heat that this new one does. I mean, the difference in heat output is like night and day.

 

[BrotherBart]

The air is cooling the thermo and the stove top sonny. I could turn the blower on on my old insert or I can turn it on on the 30 and the thermo on top in the air path goes down significantly.

Using the IR thermo it tells me that the air is cooling the thermometer even more than it is cooling the stop top.

I need to get a life and quit looking at this stuff. :lol: Oh, that's right, I already had one.

 

[Hogwildz]

Well now I am really stumped!! I have my thermomoter on the top of the insert and never get it past 500F. But there is plenty of heat, so much that if my face is at that spot where the blower is shooting the hot air out,, it damn near feels like a "burn"..

Could the air from the blower passing over the thermomoter be cooling the reading?

Guess I could try a door reading, and a top reading without the blower running. Thing is, it`s so damn cold around here right now that I am keeping that blower running from mid to high non-stop.

Here is why I am puzzled? With the old non-epa insert I could only place the therm on the door and got readings of 450F consistently. But that insert did not produce near the heat that this new one does. I mean, the difference in heat output is like night and day.

Sonny,
I am not sure of your insert, but mine has a separate steel metal plate shelf on top that has a small gap between it and the actual insert box. I would never be able to get a decent reading that I would trust.
And would have the same result as you. Unless your actual fire box top is where your putting the thermo, your getting a bad reading.
And as the ol wise feller BB says, that thermo is getting wind chill from the blower if it blows out at the top.
Did the old insert have secondary burn? The older pre EPA stove were stuff and burn, stuff and burn, with most of the heat going up the chimney and not hanging out and building up in the box along with the scorching secondary heat the new EPA stoves do. Not knocking older stoves, as I am sure many burn fairly cleanly while very hot, but I still think much more heat was going up & out than being retained longer in the box like newer ones.

 

[Pagey]

Thanks for that info. I can't really fit mine on the front of my Endeavor, so I was curious about this issue. Not saying that this experiment holds true for my stove, but it's better than no info at all!

 

[kenny chaos]

On my lopi liberty I do both flue pipe and stove top. I know the firebrick on top does not extend all the way to the front and I started measuring the stove top on the front, right hand corner. I leave it back from the front edge due to the overhang. I then read in the owners manual to measure in the center, over the door, back of the edge. The temps were about 100 degrees higher there. They also seem to run about 100 degrees cooler with the blower on.

 

[begreen]

Just checked on the T6. It's currently at 500 on the stove top and 300 on the door. 675 on the glass pointed at the fire. I just reloaded the stove so I will check again once the top is back up to 650.

edit:
I just put some of our madrona stash on the fire. Stove top now at 650, door is at ~400 and through the glass is reading about 700. If I open the door it's dang too hot to read and will singe the hair off your knuckles at 24" away. Love hardwood.

 

[bokehman]

through the glass is reading about 700.

You're not reading through the glass, you are reading the glass. Open the door 90 degrees (so the fire is no longer behind the glass) and read the same spot on the glass to see what I mean.

 

[oconnor]

I found the same behaviour on my Kennebec 450 - about 100-150 cooler at the front than when next to the flue outlet. Being next to the outlet gave good protection from blower cooling too.