Temperature swings: Stove top & pipe

I'd pay the most attention to the STT...just paying attention to the pipe only for temp extremes...

 

my mag therm usually reads 1/2 of what the flue probe reads

 

Okay I'm confused no, this is not abnormal, these convection tubes you talked about? I'm wondering if these are much like the convection tubes in EPA stoves. Which would explain the situation completely. Once you get the inside of the stove above xxx? degrees. The smoke itself burns. Putting off more heat and cooling stack temps. Much like a cat stove.

I think this is what happened, I think what you experienced was just a really efficient burn. What we all strive to achieve.

 

A convection tube is a tube that goes through the firebox...but the air going through it is external...they provide no air to the fire. Its basically just more HX area...

 

Which this is what makes me uncomfortable about these modern stoves. They cruise at these high STT leaving, in my mind, not near enough room before reaching that over-fire spot on a modern stove. I'm not saying that is what they do … rather … they make me feel uneasy in that regard. Maybe I'm worried about nothing.

Either way, old or new stove, those temps on the STT are too much for this house given the same size stove. I have too much stove and I know it, but it's nice when it gets super cold like recently.

 

This was how my the inside of my chimney looked before burning that wet wood last year for 4 hours.

I've only burned the stove this year for about 9-12 days and not all of that was 24/7.

 

That is correct.

The tubes that go through the fire box in this stove come from under the stove floor up the back slightly and angle 45* into the fire box going out the top of the fire box into the convection top where hot air is expelled. I'll try and get picture posted.

 

I think that your stove pipe exhaust temp is being regulated by the capacity of the heat exchange tubes. Those tubes and the air running through them have a capacity and rate at which they can extract the heat. So with a slower draft, less exhaust going by, they can remove the heat from the exhaust and keep the exhaust temp down. When you open up the firebox air intakes the exhaust becomes faster and the tubes are not able to reduce the temp as much. I think that if you engaged the fan you will find your exhaust being cooled even more.

 

True, but running the stove at 400*F, depending on how I set the manual damper, the exhaust already stays well below 300*F already. I have to close the damper about 1/2 way in order to get the stove to come to temp or I have to put way too much wood in it … at which point everything gets too hot … the stove … the pipe … the house … so I like to load it with a few pieces of wood, get some coals, reload lightly and keep it near 400-450ish by tending more frequently.

That makes me worry about creosote forming in the chimney and in fact I can stand outside and see evidence of brown streaks coming from the corners of the clay flue liner. If I take the STT to 450*F I can still keep it below 300, again, depending on how far I close the damper. If I run the stove hotter than 450*F+ in 20*F+ OAT temps the stove runs me out of the house … so 450ish+ STT I can bring the pipe temp up to 300-325 … takes 475*F STT to get the pipe hotter. Even with STT at 400*F she's cranking the heat out of those convection tubes, from the top of the stove, even without the blower. I get your point, but I don't really need the blower, not even with the -27*F temps we had a few weeks back.

 

It sounds like you simply have too much stove for the application (as you've stated) and maybe underestimated its overall performance capability / flexibility. In my way of thinking (and experience), a stove itself should retain a higher operating temp than the flue once fired up and cruising. After all, it's heavy steel or cast iron and the flue pipe is typically just 24 gauge thinwall vent pipe unless, of course, you're using double wall. Double wall would obviously read way lower with a mag mount thermo and requires a probe type thermo for anything close to accurate. That said, a cooler than expected flue temp doesn't automatically create creosote like many people think, (or would have you believe). It's what is going up a cold flue that creates problems. A real nice clean burn with a decent STT and a relatively cool flue temp is what you want unless just firing or reloading. Your temps don't seem out of the ordinary at all to me. But as stated, the mag thermos are frequently less than accurate -- especially at their extremes. They seem much closer in the desired burn range among the various brands I've used. Another major characteristic of the mag thermos is their susceptibility to surrounding air flow. Just aiming a small fan at your flue pipe where the thermo is placed can knock the temp reading down a couple hundred degrees on the thermo in just seconds while the pipe itself may only be affected slightly. An IR thermo is necessary to verify the readings until one gets the hang of their particular mag unit as you've no doubt discovered.

Regarding your temp variations, I'd lean toward agreeing. What I would be a little concerned about is that offset between tiles as shown in the pic of your chimney. That just doesn't look right to me. Maybe others will chime in with a more comforting explanation. Mighty clean chimney otherwise!

 

There are several of those off-sets and I'm not sure why, though I have a hunch. Supposedly the chimney liner was backed with mortar all the way to the top. I hope not as it will alter my time in doing what I have in mind.

Chimney is so clean because it was barely used after being built in the mid-70's. That picture, the chimney probably had only been used 2-3 times in the last 25 years.

Will try and get a picture of inside of the stove. I keep forgetting it.

 

Forgot to ask..., was all the wood completely burned?

 

Sounds like a learning curve to me, running a stove with only a few pieces of wood at a time makes for a different type of burn, I get some really hot fires doing it that way.

 

Sorry for the delay. Here's a picture of the inside of this stove. Note the 3 fan blades behind the screen under the ash lip. Firebox bottom is brick lined but is apparently above a hollow stove bottom that draws in cool air into the tubes you see inside the stove. I removed these door gaskets and replaced them as well as made some modifications to the window area of each door. I modified them with a 1/4" backing plate to hold in the steel window plates and added glass gasket material around the plates after grinding them for a better fit. No picture of these modifications yet. Note also that the smoke shield/baffle still needs repairing as can be seen with the right side tack weld being loose. This convection top works very similarly to modern Lopi Liberty/Endeavor models in that air is naturally drawn through this stove from bottom, and into tubes going through the firebox as can be seen in the photo below, and out through the top; cold air from the bottom, warm air out the top. The hotter it gets the faster the air flow...plus if needed...and since this stove is so big for my house...too big...the fans are not needed...but I have two fan speed options as well if and when I need them.


I'm going to replace this stove with something else. Likely an anthracite coal stove of some sort. However, I am considering an over-haul and some more modifications maybe.

 

One of the drawbacks of this stove's design, in my opinion, is the tubes inside the stove. As good as they work for heat exchange, if one of them ever burns through and gets even a pin hole in it, or worse, that could potentially be very dangerous.

I seen another stove like this online somewhere that had similar heat exchange tubes in it, but I don't really recall the name of that stove. It may have been an Ashley, but I'm not certain.

 

This is a better picture and happens to be a picture of an insert model I found on google. Note that my firebox is square unlike the insert pictured. The three tubes are the focus here as they exit at the top of the stove pushing heat into the room. They pull cool air from underneath the floor of the firebox very similar to how a Lopi Liberty/Endeavor works. I found several insert photo's of this stove today on google. I've only seen less than a handful of the stoves online. Mine appears to have been an earlier model with a flat "unrolled" edge. One stove I kept the photo of had rolled front edges.



There seems to be very little information about these stoves. Mine does not have a tag on it anywhere and no indication there was ever a tag on it. However, on the pictures I saved of the insert below, it has a Wernock/Hersey tag on it.