Open space under firebox

[ascutneymaple]

My new(to me) evaporator arch has no bottom under the firebox, this isn't a problem because it can sit on the concrete floor and be closed on the bottom. However, when I bought it I was advised to put the arch on cinder blocks or something to allow air to enter through the bottom of the firebox and create draft. In a time when everyone is trying to airtight their arch this seems like a bit of a backwards school of thought. Just looking for opinions/suggestions.

[maple flats]

If you will not have forced draft of any type, you need an adjustable air inlet. Does the front have a draft door? If yes, do not add extra. If no, you need air in but make a way to control the air. The size should be the same sq inches as the stack above the taper. The area of a circle is 3.14 x (rxr). For example, a 12" stack, r=6, 6x6x3.14=36x3.14=114 sq in. (rounded up). Make the air inlet about 114 sq inches.

[ascutneymaple]

it has a blower going from the back of the firebox under the grates and yes, it does have an ash door on the front

[Flat47]

Perhaps something was "lost in translation" because the only real reason I see to put a rig up on cinder blocks is to get it up to a more user friendly height. This doesn't apply to larger rigs, like 3x8 on up, as they are already built higher. But small rigs always seem to be too low. The draft door lets the air into the firebox, not space created by blocks.

Traditional wood-fired arches have been built with open bottoms for a long long time. I think you may have gotten some misleading advice. Check the Leader web site. They have downloadable instructions on evaporator set up. Could be helpful.

[Bucket Head]

Many folk's put their smaller rigs up on blocks to aid in firing. It used to be common practice to put rigs with no ash box up on blocks to increase the amount of area that draft air could enter under the grates. This was prior to forced draft factory rigs and the homemade funace blower set-ups. Once in a while you will still see an arch set up this way- usually in a sugar house with no electric service. It works well, you just have to be careful of the pile of red hot coals on the floor under the arch. Don't wear your rubber boots!

Steve