AUF/AOF for barrel stove evaporator

[crowellsr]

How many CFM should I be looking for in a AUF/AOF modification to my barrel stove evaporator?

[RileySugarbush]

Almost any additional air for AUF in a small evaporator like that will make a difference in evaporation rate. I would look for a cheap 200CFM (or more) squirrel cage blower and put a damper on the inlet to the blower to fine tune it. Too much air and the fire is really putting out the heat but it blows right past the pans with the high velocities and you end up with high stack temps and wasted wood.

I think it will be difficult to see any advantage of a high pressure AOF system on a short system like a barrel. Save the time, complications and money for when you have at least a 2x6.

[crowellsr]

Ok so anything is better than nothing in a AUF modification. I currently build the fire on the sand in the bottom of the barrel. Will I need to put in a grate to get the fire up off of the sand so the AUF can get under the fire better?

[Super Sapper]

Raising it up is a good idea even if you do not use AUF.

[crowellsr]

What is recommended for a grate so it is not effected by the heat?

[BRL]

A lot of people use 1/4" angle iron in this configuration VVVVV. Ashes build up in the V and keeps them cooler so they don't deform

[berkshires]

What is recommended for a grate so it is not effected by the heat?

Other people have fancier stuff, but I made one out of fencepost that works great. I drilled extra holes and left space between the beams. Looks like this:






Because of the shape, they don't buckle in the heat.

[crowellsr]

Thanks everyone! I guess I better get to work

[RileySugarbush]

You definitely want a grate. Beneath that is the " under" of AUF, so that is where you introduce the blower air. I use the inverted steel angle mentioned here. It works well. Mine have gaps of about 1/4 to 3/8 inch between angles. The area under the grate needs to be closed off so all the air goes up through the wood. many, including me) block off the very front of the grate near the door so the airflow can't short cut past the wood in that area and to keep the door cooler.

Depending on your stack and the draft it creates, you may need to throttle the blower to keep ash from blowing out the gaps around your arch. Else you need to seal things up well.

[wobbletop]

I used a small bathroom vent fan for AUF. It uses a 3" vent pipe. I plan to add a variable speed fan control to it this year. Previously I had just blocked part of the inlet.

I used a BBQ grate for the grate. You can pick up replacement ones at home depot, etc. There is some drooping but I flip it over every batch so it's not an issue. They last a couple years.