Warped Grates

[Donk4kyv]

This is the 4th year I have used my Harman Oakwood stove. At the beginning of this burning season I replaced the grate; over the past three years the original had gradually warped so badly that it bowed up almost 1 1/2 inches in the middle, making it difficult to thoroughly rake the ashes and judge the depth of the coal bed. I thought maybe I had inadvertently over-fired the stove in previous years, but this year I have been extra careful with the new grate, plus this winter has been so mild that I haven't run it all that hot. I just checked when I swept out the fire box this morning, and the new grate is developing a warp, although so far only about 3/16 of an inch.

In both cases, it arched upwards at the middle, so I suspect the top side of the grate in contact with the hot coals gets slightly hotter than the bottom side facing away from the fire, and the long-term difference in expansion eventually causes permanent warpage. I'm going to try reversing the the grate each time I let the fire go out , and see if alternately exposing each side to the fire might keep the warp balanced out even over time.

I'd like to hear from anyone else's experience with this problem with whatever stove you might be using. Does anyone know what material these grates are made from? My new one appears cut from a sheet, not cast. Certainly the manufacturer could have figured out by now what material to use that would be less prone to warpage.

I also wonder if the badly warped grate could be heated to high enough temperature that it could be forced back in shape; I'm thinking of a friend's forced-air blacksmith forge that he fires up every summer to demonstrate horseshoe making.

The guy at the store that sold me the new grate asked me if I ever burnt hedge, warning me that it would over-heat the stove. I had used a lot of hedge that first year, but didn't notice the warp until the middle of the second season. I still occasionally burn maybe one stick of hedge mixed in with other wood, and don't run the fire all that hot, so I can't see how that would be a problem. This year I have been burning mainly red oak along with a little sassafras.

Don

 

[bholler]

Most of the harmans I work on are warped the only ones that are not are people who don't use the ash pan and let a layer of ash over the grate.

 

[FPX Dude]

I had a grate then decided I didn't need it, took it out...try that!

 

[bholler]

I had a grate then decided I didn't need it, took it out...try that!

no this grate is part of the stove and is nessecary

 

[begreen]

How tightly does a new grate fit in the base cavity? Is there plenty of room for expansion?

 

[branchburner]

I bought my Oakwood used, with one season on it. After purchase, i discovered the grate was severely warped, and thought "oh no, this stove has been badly overfired!" But after buying a new grate and burning one season, THAT grate was moderately warped, and I was pretty sure I had not overfired the stove to any real degree.

Since I had not thrown out the old grate (I never throw anything out) I decide to try pounding it flat with a sledge. It did regain some flatness without breaking. The other thing I did was flip it over in the stove, to reverse the side facing the coals as you suggested, but I can't recall if that reversed the warping or not. But it's nothing to worry about.

Did you save the warped grate? One thing I had not liked about the Oakwood in trying to build a coal bed was how easily coals slid through the grate into the ashpan, so I decided to lay the old grate over the new one, in reverse pattern so as to greatly reduce the size of the openings. I figured two would be better than one, and it didn't reduce the firebox height by much. That system worked "grate."

I have also let ashes build up, and not used the ashpan at all, and got the feeling that it make the stove run better when the ashpan was full. The insulating effect means less heat dispersed below the grate, when the ashpan is empty, and more heat concentrated to the rear shoe brick area for quicker/better secondary burning, IMO. As bholler says, that would also reduce the intense heating of the grate.

Probably because it's a downdraft stove the bottom of the firebox gets a bit hotter than other stoves, and maybe it's the material or how they're made, but it seems normal for Harman grates to warp under conditions that would not be overfiring. I have not seen it in other stoves. I just had a used Jotul that leaked a bit of air and ran hot, and I'm sure the last owner overfired it... he hinted as much, and the top baffle plates were warped to hell... but the ash grate was flat and perfect as could be.

BTW, have you ever checked the external temp of your rear burn chamber? I was mentioning in another thread that's how I know the AB is firing well, but I have seen it as high as 850f when the stove top was much lower. These can be hot stoves, as I'm sure you know.

 

[Donk4kyv]

I kept my old grate, if the black hole that floats around inside this house hasn't sucked it up. I have thought of trying to heat it over a forced-air charcoal forge like blacksmiths use if I can borrow one, and seeing if I can pound the red-hot grate flat with a hammer.

From the looks of the new grate, it isn't cast but cut from a sheet, although I can't imagine what kind of cutter they would have used to stamp out something from a sheet that thick.

The warped grate isn't really a problem, other than knowing that it should be flat. It's just annoying and in the way when I rake ashes with a poker.

 

[rwhite]

I read something similar when I was looking at a jotul. Some suggested flipping it over every season.