There is a Direct Air box that works with all the Dwarf stoves: S (3kw), M (4kw) & L (5kw).
DWARF Direct-Air Intake Box
$75.00 – $95.00
The Direct-Air box connects to the back of the Dwarf stoves allowing fresh air to be piped into the stove for combustion. Supplying outside air keeps your warm air in the room instead of sending it up the chimney to be replaced by cold drafts entering your space through cracks around windows and doors. If your space is very airtight, the direct air intake might be necessary to ensure the stove gets enough fresh air to function.
You can use 3″ flexible aluminum dryer vent to make the connection between the Direct-Air kit and your outside air supply. Alternatively, if you prefer a more rigid pipe that matches your stove, the female end of our 3″ single-wall stovepipe fits nicely over the inlet of our Direct-Air kit.
Direct Air kits are designed to fit each stove model (S, M, & L) respectively. If you have a legacy Dwarf stove (one with a single air control lever on the bottom instead of two), the direct air for the Dwarf S is backward compatible with your stove.