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HVAC Unit 31 Gas Heat

The specific gravity of natural gas is?

The specific gravity of natural gas is 0.60

What is a water and digital manometer?

A water or digital manometer is an instrument that measures gas pressures.

The pressure at the manifold for natural gas is?

The pressure at the manifold for natural gas is normally 3.5" WC (water column).

What is the approximate oxygen content of air?

The approximate oxygen content of air is 21%.

Why is excessive air supplied to all gas burning appliances?

Excessive air is supplied to all gas burning appliances to support combustion.

The purpose of a gas regulator at a gas burning appliance is to?

The purpose of a gas regulator at a gas burning appliance is to drop the pressure to the proper level (in. WC) and maintain this constant pressure at the outlet where the gas is fed to the gas valve.

Do all gas valves snap open and closed?

...No,They are electrically operated

What is a redundant gas valve?

A redundant gas valve has two or three valve operators physically in series but wired in parallel with one another. This built in safety feature allows any operator (pilot or main) to block gas from getting to the main burner.

What is a intermittent pilot gas valve system?

An intermittent pilot gas valve system lights the pilot every time there is a call for heat by the thermostat. When the call for heat ends the pilot is extinguished and does not relight until the next call for heat.

What is a direct burner gas valve system?

In a direct burner gas valve system the electronic module or IFC lights the main burner directly without a pilot flame. A spark, hot surface igniter or a glow coil ussually accomplishes ignition.

Where are inshot burners used in heating applications?

Inshot burners simply slip over the orifice spuds and are screwed in place.

What is an integrated furnace controller (IFC)?

An integrated furnace controller controls the ignition and sequence of operation of most modern gas furnaces.

If there is too much primary air, the gas
flame can ____.

a. get blown out
b. "lift" off the burner rack
c. make noise
d. both b and c
Answer : D

A furnace with a vertical air flow through the
heat exchanger and the blower compartment beneath the heat exchanger is called a(n) ____.

a. uniflow
b. downflow
c. low boy
d. horizontal
Answer : B

The proper color of a gas flame is ____.

a. sharp all blue
b. lazy all blue
c. blue with slight orange tips
d. lazy with yellow tips
Answer: C

Primary air adjusters on atmospheric type
gas burners are usually ____.

a. butterfly shutters
b. sliding sleeves
c. spoiler screws
d. all of the above
Answer: D

The orifice is a precisely sized hole in the

a. manifold
b. spud
c. burner tube
d. combustion chamber
Answer : B

. In a conventional gas furnace, the hot flue
gases are ____.

a. forced out a PVC vent with a blower
b. recycled through a secondary heat exchanger and
then vented through a draft diverter
c. forced through a type B vent by a blower
d. vented by natural convection
Answer: D

A condensing gas furnace uses ____ from a
condensing type heat exchanger to increase the furnace efficiency.

a. sensible heat
b. latent heat
c. superheat
d. sub-cooling
Answer : B

If flue gases are not vented properly, carbon
monoxide poisoning could result.

Answer : True

Liquified petroleum (LP) is heavier than air
and can cause suffocation if not handled properly

Answer : True

A gas furnace designed for use with natural
gas can be used with liquified petroleum (LP) with no system modifications.

Answer : False

A gas flame will carry electrical energy.

Answer : True

. In the USA, natural gas suppliers supply gas
with a heat content of about 1,050 Btu/cu. ft.

Answer : True

The gas flame will lift off the burner and be
noisy if it receives too much primary air

Answer : True

Butterfly shutters and sliding sleeves are
examples of ___________ and are used on atmospheric type gas burners.

Answer : Primary AirAdjusters

. Three products of complete combustion of
natural and LP gas are ____,____,______

Answer : FUEL, OXYGEN,& HEAT___.

. Another name for a down-flow heating unit is


A furnace with a horizontal heat exchanger
and a propeller fan for moving air through the heat exchanger is called a ____________________.

Answer : Air Handler

The dangerous by-product of poor
combustion of gas is ________________


Spark ignition is important for roof top or
package units located outdoors because of ______________


On a gas furnace, what energizes the blower
motor in the heat mode?

Answer :Time Delay Fan Switch Temp.Sensing element

When a gas furnace ignites and is under "full-
fire," why does the fan not come on immediately?

Answer :To allow time to heat up before pushing hot air out thru the vents

What is the difference between a yellow gas
flame and an orange gas flame?Yellow indicates not enough air,Orange indicates dust particles being burned

Answer :Yellow indicates not enough air,Orange indicates dust particles being burned

The flame in a gas fired furnace is burning
with heavy yellow tips. What is the problem?

Answer :Not enough air & emitting carbon monoxide

While the furnace is operating, heated air
and flue products spill out of the burner compartment. What is the problem?

Answer :Too much air across the heat exchanger,the flue gases will become too cool& the combustion will
condense and run doun the flue pipe

When the burners ignite, the burner flame is
normal until the blower starts. At this time, continuous roll out occurs. What is the problem?Too much air in the

Answer :A Crack in the Heat Exchanger

Why do propane and butane gas furnaces
require 100% shut off in the event of pilot outage?

Answer :The gas is heavier than air,it will not vent up the flue ,gas can pool & create an explosion

return and supply ducts are both on top

a. up-flow
b. down-flow
c. low boy
d. horizontal
Answer : C

blower located below heat exchanger

a. up-flow
b. down-flow
c. low boy
d. horizontal
Answer : A

primarily used in crawl spaces

a. up-flow
b. down-flow
c. low boy
d. horizontal
Answer : D

blower located above heat exchanger

a. up-flow
b. down-flow
c. low boy
d. horizontal
Answer : B

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