Outside air and "port" for Hybrid Stove

[00nothing]

Hi Max and everyone,

I’m finishing up a foundation for the Hybrid stove and am at the stage of placing the top slab of the foundation. I’ve decided to try to work in an outside air intake (a 6" round duct) and am thinking through the placement of the duct in the slab. My instinct is to offset it to the firebox side of the stove so it’s directly under the grate and a bit towards the rear of the plan in the N-S axis. On the drawings, there’s a note for a “port” on Section 6 and I’m guessing this is a secondary air port behind the firebox, but I’m not totally sure what’s all being called out on that drawing. Where would that “port” air normally enter from in a build that didn’t have any outside air, behind the ash box, somewhere else?

Thanks for any advice!

[max]

Hi Oliver. This is a great question.

Whereas I generally favor bringing outside air directly inside the stove, the two (or three) different burn modes of the hybrid cookstove masonry heater design will likely require that outside air be brought near to the firebox and ash doors, but outside of the stove. This will allow each of the doors to operate as air controls.

I have been meaning to update this drawing (which was originally published in the design’s development topic):

If you ignore the cooktop as an air intake, the illustration shows the burn configuration in mass heating mode. This is basically a self-feeding batch box with primary air coming in through the door and secondary air coming through the grate.

What the illustration does not show is what happens when you reverse the flow using dampers upstream in the design to move into cooking mode where the flames are traveling upward towards the cooktop. In this configuration, the ash door and grate administer the primary air and the door administers the secondary air.

This dual function is one of the main innovations of this hybrid design.

I was extremely impressed with the quality and apparent cleanliness of the burn in both of these configurations in the prototype that we built at the MHA annual meeting.

So far in its design development, this would require that outside air come up through the floor right outside and at the base of the stove, likely in the tile work of the required hearth extension.

There is a piece of hardware that was designed specifically for this purpose that I don’t believe is currently available:

It was designed to cap and regulate a 4” outside air feed in the floor in front of a stove.

I hope this provides some insight.
Would be really neat to see progress on your build. If you feel the calling, start a new thread with progress reports! Will try to cheer on and provide info. in the process!