Wednesday, March 16, 2011

Bus Blog 19: The Stove

I picked-up a lot of things during my first permaculture design course, the heaviest of which was an old cast iron stove.  I found it half-buried in a hillside on the Mountain Waters property and Richard, the owner, said I could have it.
The stove was rusted, plates on the inside where cracked and burnt clean through, it was missing the range top and was loaded with dirt, ash and decaying plant matter.  It was beautiful.  A pair of fishermen were cast in the walls, pulling in their net and covering the various chimney ports were rusty seagulls.  The adjustable stove door read "ULEFOS".

 I got a little obsessed with the rocket stoves during my stay at Mountain Waters.  I read everything I could about them and the logic made sense: use controlled air intake to convert your fuel to fully burnt hot exhaust gas.  You can then channel the exhaust gas through a series of twists and turns of piping to extract maximum heat from it.  The more mass your piping possesses, the longer you can store and release this heat into your atmosphere.  Rocket stoves and heaters enable people to produce more heat with less fuel.  There's a great book the mass heating concept and how to do it here.  I wondered if I could turn the Ulefos into a rocket stove.

Further research revealed that the model of this stove had been in production since 1766 with no changes and was a huge seller until the 1950's when wood heating lost popularity to gas and electric.  200 years without a change in design?  It must have worked.

Not wanting to mess with two centuries of success, I tried my best to restore the stove to original condition and not to convert it.  First, I stripped the stove down to pieces, wire brushed and sand blasted each, then reassembled it using High Temp RTV to seal the unit.  The broken plates were replaced with 3/8" steel and held in place with refractory cement.  

To secure the stove in the bus, I anchored bolts in the studs I had previously placed beneath the fire-surround floor, then welded a series of washers to the stove's feet.  Once the stove was assembled and in place, I cranked washers tight to the floor of the surround with a pair of steel hex nuts, then locked them in by tightening the nuts against each other.  I tried to shake the stove loose, but the bus just rocked back-and-forth gently with all my efforts.  It was in.

Next came the chimney.  I had been pricing stove pipe all round town and if a store actually had my size (4") it was ridiculously expensive.  I made a mistake in this, for some reason I ignored all my junk shop/yard experience and searched only box stores and hvac places for the proper pipe.  Once I was sure that I'd go broke using a conventional chimney, I did what any cheap person would do.  I decided to make my own.

It took me less than 5 minutes at the scrap yard to find the pipe that would become my chimney.  It was 4" outside diameter with a 1/4" thick wall.  This meant that the pipe was heavy, but strong.  It also had a lot of mass to it.  While I decided against modifying the Ulefos to function as a rocket stove, it seemed I could still gain the benefits of thermal mass heating in the chimney.  The theory worked the same:  if I had a thick wall to capture a lot of heat from the exhaust gases and put a few twists and turns in the pipe to expose that heat to more surface area, I'd get more heat, longer.

I spent the next two days cutting, welding and grinding the pipe into a funky, yet serviceable shape.  After an initial pressure test, involving a bike pump and rubber stoppers, it seemed my welds were air-tight up to 15 psi.  It was heavy as hell, but seemed like it would work.  Good enough for me.

The ceiling was marked above the stove and anything flammable was cut-out and removed in an 8" radius around the pipe.  I cut the roof like dividing a pie into 8 pieces and bent each slice up and out.  The surrounding area was jammed tight with refractory grade insulation and closed with a piece of cement board with a chimney sized hole in the middle.  After working the chimney through the cement board, I climbed to the roof and sealed the chimney hole with a gasket and more high temp RTV.  I then bent the slices of steel roof down to the pipe, loaded them with more RTV and attached each with self tapping screws.  

Since the wall of the chimney was 1/4", the screws took a while to set themselves and I did a bit of swearing. People walking by were quick to look away.

We had a test fire the next day, and after sealing a leak or two, the carbon monoxide detector was silent.   There was heat.