DIY Rocket Stove - This is built exclusively from materials available from your local box hardware store etc. using stock HVAC components for about $50 with enough material left to make another and possible a third with only a few other parts.
by N&L DIY
by RubiconDave
by 3rdWorld Prepper
by Pearls and Fiddlesticks
by DIY Life Hacks
by Banshee Moon
by Tanuja's Craft