Stove top plate - the thick or thin of it

[precaud]

Functionally speaking, in most wood stove designs, the top plate is the primary heat exchanger. When we see a stove with a nice, thick top plate, I think we all associate that with "quality" and "durability." I have a theory that puts a different perspective on the value of a thick top plate, but first I'd like to get some input.

Has anyone here ever burned out the top plate of a stove? Or do you know anyone who has?

 

[EatenByLimestone]

I got rid of a potbelly that was literally worn out. The top piece of cast iron was the part that was in the worst shape, it was actually crumbling, but it didn't burn through.

I'd be happy to give more details but don't know exactly what you want to know.

Matt

 

[precaud]

Matt, was wood or coal burned in it? How long was it used to get to that state?

 

[EatenByLimestone]

Coal was burnt in it. I never saw it burning coal though. That was mostly before my time.

IIRC, the stove was a Puck 12. Judging by the time and effort needed to make the ornate castings I'm guessing it was probably 150 years old. My grandfather bought it used in the 60s (I think) when a larger potbelly that he had in there needed to be replaced. I remember him saying he paid $100 for it so it had to have been in great condition for a depression era person to part with that much cash. I believe it was ran hard the first years he had it as they used to use the cabin in the winter. In the last 30 years or so it didn't get much use since they were getting older and closing up for the winter. I only saw wood burnt, but there are still a few 5 gallon buckets of coal under the cabin. When I took the stove out, the top plate was held together with screws, rust and stove cement. The shaker grate did not move, one could see around the insglass, etc. It was long after replacement time.

I imagine it took 30 years of overfiring to do the damage. As an interesting side note the chimney was entirely 5" singlewall. Up and out of the stove, through a sheetmetal thimble and then up to the stars. I never cleaned the chimney, and have never found a brush, but when it was taken down it was very clean. I found soot filling up about 1 inch of the horizontal portion though. I'm thinking it was ran fairly hot for its lifespan.

Matt

 

[precaud]

Wow, that's an oldie indeed. And ran pretty hard from the sound of it. The $100 potbelly in the 60's sounds too high to me, but no matter.

What I'm looking for is if anyone has burned out the top plate of a wood stove in normal use.

 

[shawng111]

perhaps a thicker top plate has more to do with thermal mass than durability. just speculating

 

[precaud]

perhaps a thicker top plate has more to do with thermal mass than durability. just speculating

Good guess, Shawn. That's exactly right, though I was hoping to demonstrate along the way that it isn't needed for durability reasons.

Instead of storing heat in the firebox insulation, store it in the heat exchanger. Stretch the mass and conductivity of those two elements to opposite ends. Low-mass/highly-insulative firebox liners coupled with high mass/highly-conductive top plates. This is already being done in some of the stoves, the Quad's and PE's come to mind but there are surely others.

 

[BrotherBart]

Interesting subject. But there has to be some durability issue there also. I say that because several manufacturers offer their stoves in a choice of flat top or step top versions of the same stove. On the flat tops they use a thicker sheet of steel for the top plate than they do on the step top where the step bend lends rigidity. Most are 5/16" for the flat top versus 1/4" for the step.

 

[EatenByLimestone]

You could very well be right concerning the price.

I'd bet it has more to do with durability. In a steel box stove the most visible part is the top. If there is an obvious bubble or ripple in it they will loose sales.

With cast iron I bet it depends on the stove design. If you made top of the potbelly I mentioned above thicker, how much more thermal mass could it have? For the boxier designs I bet it's durability also. The top is fairly unsupported. At least on the bottom you can cast ribs into it while not taking up firebox room. The thicker it is, the stronger it will be. I'd bet thermal mass is just a convenient side benefit.

Matt

 

[precaud]

For the same stove body, I'd guess the weight of a 1/4" step-top and a 5/16" flat-top would be pretty close.

What's the 30's top plate thickness?

Lurking within any discussion of durability is the question of expected service life - how long should a stove last before it's recycled? It would be interesting to get the input of some manufacturers.

 

[BrotherBart]

The 30 is 1/4" on top and 3/16" on the sides. They use the secondary air manifolds for stiffeners on the sides and back of the stove body.

 

[precaud]

That should be fine, the 30 doesn't use the low-mass firebricks.

 

[EatenByLimestone]

The top of the firebricks is held in by a horizontal piece of angle iron? (can't remember and don't want to go downstairs to check) That should add some rigidity also.

The more I think of it, the purpose of the thick top could very well have changed over time. Where it may have needed to be thick to be durable on the older stoves, the newer ones have a baffle under them to reflect heat back down. This should keep a good amount of abuse away from them. Maybe it has become a giant heat sink where it used to be more structural.


Matt

 

[EatenByLimestone]

A flat top may simply be thicker because one is more likely to set a large stock pot full of water right in the center of it. :lol:


Matt and doesn't really have a position on this one.

 

[precaud]

A flat top may simply be thicker because one is more likely to set a large stock pot full of water right in the center of it. :lol:

And, it's easier to bend the thinner steel...

Matt and doesn't really have a position on this one.

Glad to hear it - the center of the stove is not a good position to take