To control the negative pressure generated by a tall stack or an induced draft fan, stack outlet dampers were installed and controlled to maintain a setpoint typically about 0.1” negative pressure measured at the back of the furnace. Boilers made in this era typically had tall stacks to induce a negative pressure (or draft) in the boiler, or induced draft fans. Allowing these furnaces to “go positive” for even a short amount of time could result in damage to the boiler casing or injury to boiler operators. Because the furnaces were not air tight, the furnace walls were kept cool by a constant stream of cool air drawn in by the slightly negative pressure of the furnace. Namely, boiler construction. Since then, many more boilers were of brick-set construction, required to be run at negative draft or balanced draft pressure. Today, draft controls are still common on all types of boilers, but for very different reasons. (Heating oil was 25¢ a gallon in 1964!) Additional benefits included more reliable burner performance, reduced burner emissions, and increased safety by tripping a boiler off line if the draft turned positive.Ĭheck out the first page of that article below. Keep reading to the next section to learn how to maximize the efficiency of your electric furnace.Danbury, CT – In 1964, Preferred Instruments published an article in the Fuel Oil & Oil Heat magazine. During that time, draft controls were used primarily to control excess draft from tall chimneys and lower excess air to conserve fuel. Electric heat is in some ways much simpler than either gas or oil, but it can still have its fair share of problems. Set the upper pointer at about 115 degrees Fahrenheit (46.1 degrees Celsius) and the lower one at about 90 degrees Fahrenheit (32.2 degrees Celsius).ĭo not try to adjust the burner of an oil furnace call a professional service person.įinally, we have electric furnaces and heaters. Pointers should be set about 25 degrees apart. There are two pointers on the fan side the blower turns on at the upper pointer setting and shuts off at the lower pointer setting. One side is marked LIMIT don't touch this side. To do this, remove the control's cover and find the toothed dial underneath. If the blower control has been set to ON, change it to AUTO if the blower control is already on AUTO, the limit switch needs to be adjusted. To determine the problem, check the thermostat. If the blower runs continuously, either the blower control on the thermostat has been set to the ON position, or the limit control switch needs adjustment. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. If the plenum gets too hot, the limit switch shuts off the burner. The limit switch is a safety control switch and is located on the furnace just below the plenum. The draft regulator should be adjusted by a professional service person as part of regular annual maintenance. To decrease airflow, turn the counterweight outward. To increase the airflow, screw the counterweight inward. Too much air in the chimney wastes heat too little air wastes fuel by failing to burn it completely. Accumulated soot and rattling are signs that the draft regulator needs to be adjusted. The draft regulator, located on the stack, is closed when the burner is off but opens automatically to let air into the chimney when the burner is turned on.
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