another hot floor... or "Tale of two Jotuls"

So, I noticed this evening that the floor under the "new" Jotul Firelight 12 is much warmer than I'd ever noticed the floor getting on the old stove, so I took some measurements. Both stoves were started cold at the same time, roughly 3.5 hours ago, and both reloaded with a big load approximately 2.5 hours ago. Both have been cruising the last 2 hours with stovetop ~550F and catalyst 1200 - 1400F. In other words, all conditions are roughly equal... with one exception. The old stove has a nice bed of ash from several weeks of burning, whereas the new stove only has minimal ash bed from one half day of burning.

Here are my measurements, all in °F:



The new one seems to be running awful hot for any stove requiring only ember protection. There's no mention of a bottom heat shield for this stove, and externally, everything looks similar to my old stove. I know the ash bed probably makes a difference, but I think 275 on the bottom of the ash pan, and 150 on a masonry floor below is awful hot for any stove requiring only ember protection. No?

begreen said:

It's a bit warm, but not alarming yet. The floor under the stove is stone, right? How is the stove working out in that room?

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Yep... not alarming for me, but perhaps a sign that something is not right with one of the stoves. The floor beneath the stove is brick tile, then masonry board, and then several feet of stone, supported by some heavy wood timbers. The floor out in front of the stove has only the brick tile and masonry board atop wood timbers, without the benefit of several feet of stone, but it's not getting hot out in front... just directly underneath.

Too early to say how the stove is heating from that room, as I've only run it a few times when I can be home. I'll start fueling it 24/7 this weekend, which -- given the massive amount of stone I have to heat -- will definitely change the dynamics a bit.

cc rangeley said:

I learned that the reason for my hot floor under my jotul was because bottom heat shield was missing (and still is). Jotul folk said it's still safe on only an ember pad and not to worry about it.

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Yep... I was on that thread! Hence the title of my thread, "another...".

jotulguy said:

Just a thought....but is there ash in stove #1 and little to no ash in stove #2? Ash is an amazing insulator.

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Ash will definitely make some difference, but the question is more whether any stove with ember-only floor rating should hit 375 on the bottom side, ash or no ash.

edit: okay... maybe not "several feet" of stone below the stove, as I just found this photo of the basement below the fireplace. What looks like a fireplace next to the built-in cupboard in this photo is the foundation for the fireplace above, where I have the stove installed. Eyeballing, looks like maybe 24" -28" of stone between the firebox floor above and those heavy timbers supporting the stonework.

These stoves have two bottom plates, the upper one being the floor of the firebox, and a second about an inch below, forming a plenum for intake air to flow in-between. Air is drawn in thru two holes in the rear of the stove, channeled around either side of the ash pan between these two bottom plates, and rises thru channels on either side of the front door to supply the firebox thru the air wash system above the door. Air is also taken from this space between the two bottom plates to feed the cat in the rear of the stove.

In any case, I got to thinking about this hot-bottomed stove, and realized it's this double bottom plate, and the intake air that's constantly funneling thru it, which keeps the bottom of the stove cool, thus permitting the ember-only clearance. On the hunch that maybe something was clogging this plenum and causing the warm bottom (lack of cool air running thru), I decided to hook my shop vac to each of these two holes after work, before I lit the stove for the evening. Some crap definitely came out of the holes, but nothing that sounded like it would have really been a plenum clogger (was expecting a dead mouse, actually!).

Then, I lit the stove and I used my IR gun and the FLIR camera to measure temperatures on the bottom of the stove. Measuring on the bottom of the stove, as well as on each of the legs, the left side of the stove is running 30 - 50F hotter than the right side, making me think that perhaps air flow thru the left side is somehow less than the right. Perhaps there's a clog there, which the shop vac failed to clear?

Other than the hot floor issue, this stove is running BEAUTIFULLY! Gets up to light-off temp way quicker than the other, and I seem to be able to cruise way lower, way longer, and with much lower stove-top temps than the other, older stove. Could be the extra 10 - 15 feet of chimney, or it could be the stove. I'm not swapping them this week to find out.