In some furnaces, an opening in the flue, called a(n) ____, helps keep constant pressure in the combustion chamber and prevents ambient air from reaching the furnace flame.

A humidifier that sprays small water droplets into the air is called a(n) ____ humidifier.

A typical forced-air furnace is equipped with a(n) ____.

It is very important to install a humidifier’s ____ level.

Which type of furnace can operate to produce either full heat output or produce at a fixed level that is less than full heat?

A Category I furnace is a ____ furnace.

Which of the following statements regarding hot-surface ignition (HSI) systems is false?

A combination gas valve is used to replace separate furnace components, such as a ____.

A furnace that can vary its heat output along a scale that may range from 40% to 100% capacity is a(n) ____ furnace.

A furnace with an AFUE rating between 90% and 97% is a ____ gas furnace.