TESTING CREOSOTE-REDUCING DEVICES: THE RESULTS

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The Smoke Consumer reduced creosote, too, but did so less well than the other two devices. In price, it falls between the draft control and the catalytic afterburner.

The Smoke Consumer required considerably more effort to operate and maintain than the other products tested, since it didn't always self-clean during the hot fires that started off each day's run. The manufacturer's literature specifies both 300 and 450°F as the surface temperatures needed at the filter level to assure that the deposits on the filter will ignite and burn off. (We understand, from the manufacturer, that 450°F is the current recommendation.) During our daily hot fires, the surface temperature on the devices always exceeded 300°F and usually exceeded 450°F . . . as measured with the surface thermometer supplied by the manufacturer. Therefore, our experience with the Smoke Consumer leads us to conclude that even 450°F isn't hot enough to guarantee ignition of the deposits in the filter.

When a Smoke Consumer is installed and operated in a house, part of its creosotereducing effect may be due to the recommended daily hot fires themselves (if such a procedure wasn't part of the home's daily woodheating routine before putting in the device). More intense burns-which result in more complete combustion of the smoke-not only generate less creosote, but cause high flue gas temperatures that pyrolyze or dry up the existing deposits so that they lose weight and adhere less strongly to the flue wall.

LIQUID CREOSOTE AND THE CREOSOIE-REDUCING DEVICES

The amounts of liquid creosote that we observed in the course of our tests are, we believe, accounted for by the theories behind the design of each device. The Smoke Consumer, for example, is principally a filter for particles in the smoke . . . most of the vapors (and some of the particles) pass through or around it. In our tests, considerable quantities of the organic vapors and water vapor condensed, forming the liquid creosote mentioned previously.

The Smoke Dragon, on the other hand, destroys a portion of the organic vapors by burning them. In addition, some of the heat that's generated in the catalyst probably goes up the flue, which also decreases condensation. And finally, the secondary air that the device adds to the flue gases has a diluting effect (just as does the air admitted by the barometric draft control), and thus helps reduce creosote accumulation. For all these reasons, one would expect less condensation of creosote in the flue above the Smoke Dragon than in the flue above the Smoke Consumer.

The barometric draft control simply adds air to the smoke in the flue. Consequently, all the vapors pass through the device and up the chimney. The dilution air added by the draft regulator affects the flue gases in two ways: First, it increases the velocity of the smoke ... and second, it dilutes the gases, resulting in a lower overall concentration of unburned material in the smoke. These factors substantially reduce condensation of both water vapor and organic vapors, despite the cooler temperatures. No liquid was observed in the tees just below the prefabricated chimneys in the systems equipped with barometric draft controls . . . while there was at least some liquid in all the other systems (including the controls).

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