Coal buildup

[hpmer]

Donkey,

I took your suggestion and built a downdraft stove. Actually a mockup of what I will eventually build and am very impressed with how cleanly it burns.

After a while, however, coals begin to build up and eventually fill the fuel box. Since I only have experience with horizontal feeders I don't know if this is normal or if there are any tricks to metering the fuel at the optimal rate.

Am I just feeding it too quickly, or should I resign myself to periodically removing coals to make room in the fuel box? The stove's purpose is to boil down maple sap into syrup and that means 8-10 hour burns.

[grizbach]

hpmer, If you take a look at my stove over at the heating forum, you will see that I have built a grate with an ash drawer under it. I can dump my ash or coals when ever I want. It takes about 6 hrs to fillup. My current grate covers only about 25% of my feed area.

[hpmer]

Griz,

Is it mostly ash or coals?

I think the grate is a good idea, but that will require some redesign. Probably well worth the effort though.

[grizbach]

As the wood burns it turns to coals, which lie on the grate.
As the coals burn, they turn to ash, which fall through the grate.
You can also break up the coals into small pieces to have them fall through.

[hpmer]

What did you use for a grate?

[Donkey]

The coal buildup problem is common and there are a lot of various solutions.
I like grisbach's, it seem like one of the more practical.
For heating a space, usually by the time the coals get out of hand, it's time to shut it down anyway. Your needs will be different.
The grate is a good idea, I'd make the feed deeper just on top of the grate to make extra space for coals and give them more time to burn completely.

[grizbach]

You are going to have to use stainless to handle the heat. I made my grate out of 1/8" sheet stock.
For someone who doesn't have shop equipment, one could get some cheap stainless servingware (with long handles). Take off the handles and bend it in half or thirds (so it resembles a W) to the dimensions you want.

I'm currently working with some stainless. I could send you a short bar if you want.

[hpmer]

Thanks Griz, but I think I'll experiment with some options on my end first. I do appreciate the offer, though.