THE WORLD'S SIMPLEST 'PULSE JET' HEATER!

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The fuel supply and its control plumbing are common hardware items. We used a one- quart fuel tank for our model to limit the burning time to several hours between refills; its vented cap can be sealed for storage. With the exception of the two 1/8" brass needle valves, the metal fittings can be either brass or iron, whichever you have or can purchase more inexpensively.

To reduce fuel pressure within the feed-control lines (which could cause a too-rich burn and subsequent overheating), we packed 1/4" X 1" twisted cotton wads into the cores (it's imperative that there be enough restriction to make it extremely difficult to blow through each of the tubes). Then, to guide each drop of kerosene down the copper burner feed line (rather than let it build up at the bottom), we inserted a length of 1/16" copper-coated welding wire into the tubing.

Tackling the fabrication of a sheet-metal burner housing is a task; instead, it's easier to use a 44" length of premade 26-gauge, 3" galvanized steel downspout as a "combustion chamber" and add to it a bread-pan wall spacer and some heat-dissipating fins. The dissipater is just a 17" X 38" section of aluminum roofing fan-folded to create 3"-deep fins. The spacer should have a 9/32" hole bored through each of its ends to allow the copper fuel feed line to pass through, and have six 1-1/2" openings in its sides to let heat escape. (The compression nuts and sleeves go on after the line is slipped in place.)

To complete the housing, the burner should be installed through a 7/16" hole drilled 5" from the lower back end of the spout. Then, with two 1-1/2" holes bored to the side of that, the spring-mounted sheetmetal lighting flap can be added. After this, the inlet elbow and the exhaust elbows and stack can be attached when the unit is permanently mounted.

Note that we've included a finned chimney cap in our design. Testing reinforced our belief that this addition helped induce the flow of flue gases out of the short stack; it's made in a similar manner to the heat dissipater, but its mounting edges are folded around the top of the flue spout and secured with sheet metal screws.

To install the heater in the ice-fishing shelter or in any other single-walled structure, it's necessary to make an inlet opening in the sheathing slightly larger than the outer dimensions of the elbow. The exhaust opening, since it's exposed to considerably more heat, should measure about 6" X 6", and its four edges should be protected with sections of polished aluminum bent to create a 1" lip on both sides of the wood. For drip flashing, we chose to use two steel pie plates; we cut 2-1/4" X 3-1/2" openings in the bottoms and mounted the inlet plate outside, facing outward.

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