Heating 101

When a coffee cup gets warm when hot coffee is poured​ in, it represents heat transfer by​ _____.

• conduction

• capillary action

• convection

• radiation

Answer explanation

Conduction is the flow of heat from one material to another through direct contact. See Section 1.1.1

When you become warm while sitting some distance from a​ fire, heat is being transferred by​ _____.

• combustion

• conduction

• radiation

• convection

Answer explanation

Radiation refers to the transfer of heat through space by electromagnetic waves. Through​ radiation, heat can pass from one object to another without warming the air between them. The heat from the sun or a fireplace is a good example of radiant heat.

See Section 1.1.3

A temperature of​ 140°F is equal to​ _____.

• 202°C

• 12°C

• 60°C

• 133°C

Answer explanation

​°C =​ 5/9 (°F​ - 32)

​°C =​ 5/9 (140-32)

​°C =​ 5/9 (108)

​°C = 60

See Section 1.1.4

Next question

Humidifiers are used to​ _____.

• lower the room temperature

• reduce condensation

• keep furniture dry

• add moisture to the air

Answer explanation

Homes are often equipped with a humidifier to add moisture during the winter months when the air is​ dry, increasing the feeling of warmth.

See Section 1.1.5

Carbon monoxide​ (CO) is produced when​ _____.

• there is excess air in the combustion chamber

• incomplete combustion is present

• oil and oxygen are mixed

• there is too much water vapor in the flue gas

Answer explanation

Incomplete combustion results from a lack of oxygen and causes undesirable products to form. These include carbon monoxide​ (CO) and pure carbon​ (soot), as well as other compounds.

See Section 1.2.1

A yellow flame in a gas burner indicates that​ _____.

• incomplete combustion is at work

• there is too much primary air

• there is too much secondary air

• a proper amount of combustion air is present

Answer explanation

A yellow flame in a gas burner is a sign of incomplete combustion.

See Section 1.2.3

Most calculations regarding the capacity of gas piping are based on natural gas having a heat content of​ _____.

• ​1,800 Btus/ft³

• 750 Btus/ft³

• 1500 Btus/ft³

• 1000 Btus/ft³

Answer explanation

The heating value of natural gas varies from​ 900-1,200 Btus/ft3​, depending on the local supplier.

See Section 1.2.4

Figure RQ01

Which furnace configuration is represented in Figure RQ01​?

• Horizontal

• Counterflow

• Upflow

• Lowboy

Answer explanation

The​ counterflow, or​ downflow, furnace​ (Figure 11) is commonly used in structures with an​ under-floor air distribution system.

See Section 2.1.0 and Figure 11.

In a condensing​ furnace, the secondary heat exchanger​ _____.

• is used to reheat the flue gases before they are vented

• extracts heat by condensing moisture from the flue gases

• is used only for​ room-air dehumidification

• extracts heat by cooling the room air that passes over it

Answer explanation

The secondary heat exchanger appears much like a cooling coil. As the flue gases move through the​ coil, enough heat is extracted from them that water vapor in the gases condenses.

See Section 2.2.1

The type of blower used to circulate room air through a furnace is​ a(n) _____.

• centrifugal blower wheel with​ forward-curved blades

• axial fan

• centrifugal blower wheel with​ backward-curved blades

• propeller fan

Answer explanation

Centrifugal blower wheels with​ forward-curved blades are used in virtually all furnaces. Air enters through both sides of the wheel and is compressed at the outlet by centrifugal force.

See Section 2.2.2