HVAC Unit 31 Gas Heat Review Questions with answers
Question :The four types of gas furnace air flow patterns are
_____, ______, _______ and _______.
Correct answer:Upflow, low-boy, downflow, and horizontal.
pg 711-712
Question :Describe the function of a multipoise or
multipositional furnace.
Correct answer:It can be installed in any position. It is very
versatile. The configuration can be changed very easy. pg 712
Question :Describe the function of a draft safeguard switch.
Correct answer:Also known as a vent limit switch. They are
NC switches usually mountd on the draft hood if the furnace has one. They monitor the draft hood temperature and open when there is any spillage of flue gas. pg 713
Question :Where are auxiliary limit switches used in heating
applications?
Correct answer:They are used for counterflow and horizontal
furnaces. They monitor room return air temperature and interrupt burner operation when the temperature gets too hot.pg 713
Question :The specific gravity of natural gas is: ABCD
Correct answer:D) .60 pg 714
Question :What is a water and digital manometer?
Correct answer:A water manometer is used to measure gas
pressure. It is a tube of glass or plastic formed into a U that is half full of water. Gas pressure is determined by the difference in levels in the two columns.
A digital manometer also measures gas pressure. It does not have any fluid to spill. It can also measure both positive and negative pressures in inches of water column. pg 715
Question :The pressure at the manifold for natural gas is
typically: ABCD
Correct answer:D) 3.5 in WC pg 715
Question :What is the approximate oxygen content of air?
Correct answer:21% oxygen pg 716
Question :The typical manifold pressure for propane gas is
_____ in WC.
Correct answer:11 in WC pg 715
Question :Why is excess air supplied to all gas-burning
appliance burners?
Correct answer:To make sure that all of the methane is
burned. pg 717
Question :The purpose of the gas regulator at a gas burning
appliance is to: ABCD
Correct answer:B) decrease the pressure to the burner. pg 718
Question :T or F: All gas valves snap open and closed.
Correct answer:False - the valves are solenoid, diaphragm and
heat motor. pg 719
Question :Which of the following features does an automatic
combination gas valve have? ABCD
Correct answer:D) all of the above. It has a pressure regulator,
pilot safety shutoff, and redundant shutoff feature. pg 721
Question :What is the function of the servo pressure regulator
in a modern combination gas valve?
Correct answer:It monitors the outlet pressure of the gas
valve. Any gas outlet pressure change is instantly sensed and reflected back to the diaphragm. The regulator then repositions the diaphragm and disc to change the flow rate through the servo pressure regulator valve.
It is a self-balancing system that works off gas valve outlet or working pressure and is independent of flow rate. pg 723
Question :What is a redundant gas valve?
Correct answer:It has two or three valve operators physically
in series but wired in parallel with one another. It is a safety
