The Design Challenge Stove is carefully engineered for smoke-free loading even under marginal draft conditions:
1. The andirons tilt forward to reduce activity in the coalbed (see Blogpost: Under the Hood 3: Andirons - movable, removable, customizable).
2. We added an air foil nose on the front of the secondary chamber, and an airfoil on the face of the catalyst sled to help the exiting smoke make the turn into the bypass.
3. The bypass opening is very large (over 50 square inches). There is no flow restriction at the bypass.
4. The flue exit collar is shaped like a “funnel”. The funnel collar increases flow through the stove by about 12% when the door is open, and helps to vacate smoke quickly from the firebox.
5. Finally, for marginal draft applications (short/oversized chimney, etc.), we have added a simple hinged “smoke flap” above the door. When the door opens the flap covers the top of the door opening. When the door closes, it lifts the flap. For installations that are not at risk of backpuffing, it can be lifted above 90 degrees and a cam holds it out of the way.