What type of furnace draft uses two fans to facilitate airflow?

A. Assisted draft
B. Induced draft
C. Natural draft
D. Balanced draft


A. Incorrect. Assisted draft furnaces use rotary blowers, driven by electric motors or steam turbines.
B. Incorrect. Induced draft furnaces use a fan located at the top of the furnace to draw flue gas from the furnace body into the stack.
C. Incorrect. Natural draft furnaces have no mechanical draft or fans.
D. Correct. Balanced draft furnaces use two fans to facilitate airflow.

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The second-order AR filter has feedback coefficients a1=0.9 and a2=0.5 (b0 = 1). When xi = sin(2?i/8), the value of y2 = ________(x.xx).

Analysis: x0=sin(0)=0, x1=sin(?/4)=0.707, x2=sin(?/2)=1. yi = 0.9yi-1 +0.5yi-2 + xi. With zero initial conditions: y0=x0 =1 y1=0.9y0+x1=0.9(1) + 0.707 = 1.607 y2=0.9y1+0.5y0+x2 = 0.9(1.607) + 0.5(1)+ 1 = 2.9463 = 2.95

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Fill in the blank(s) with correct word

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