NATE Gas Heating 3

Question 1

What is the minimum clearance from combustibles required for Type B vent pipe in most residential applications?

Accepted Answer

1 inch

Answer

Type B double-wall vent pipe requires only 1-inch clearance from combustible materials due to its insulating outer jacket.

Question 2

What does a cracked heat exchanger in a gas furnace risk introducing into the living space?

Accepted Answer

Carbon monoxide (CO) and other combustion byproducts

Answer

Cracks in the heat exchanger allow combustion gases including deadly carbon monoxide to mix with circulated air and enter the living space.

Question 3

What is the purpose of the vent pressure switch on a two-stage condensing furnace?

Accepted Answer

Confirm the inducer is operating at proper speed and the vent is clear before allowing ignition

Answer

The vent pressure switch proves adequate draft by sensing the negative pressure created by the inducer blower before the gas valve is energized.

Question 4

LP (propane) gas manifold pressure for residential furnaces is typically set to which value?

Accepted Answer

7–11 inches WC

Answer

Propane furnaces require higher manifold pressure than natural gas, typically 10–11 inches WC, because propane has different combustion characteristics.

Question 5

Which type of furnace venting uses a dedicated fresh-air intake pipe running alongside the flue pipe?

Accepted Answer

Direct vent (sealed combustion) system

Answer

Direct vent sealed-combustion furnaces draw all combustion air from outside through a dedicated intake, preventing depressurization of the home.

NATE - North American Technician Excellence Practice Test

NATE - North American Technician Excellence Practice Test

NATE Gas Heating 3