Efficient Gas-Fired, Forced-Air Heating systems

Question 1

A mid- efficient furnace typically has an AFUE rating of _______.

Answer 1

80-83%.

Question 2

What does AFUE stand for?

Answer 2

Annual Fuel Utilization Efficiency.

Question 3

What is the minimum efficiency rating of a high efficient furnace?

Answer 3

90%

Question 4

What product is formed by the condensing of the products of combustion in a High efficiency furnace?

Answer 4

Carbonic Acid. (condensed water and carbon dioxide gases)

Question 5

Can you run a high efficient flue horizontally?

Answer 5

Yes, the PVC intake and exhaust are commonly routed through a side wall. This is acceptable because there is a Combustion air blower in the system.

Question 6

What techniques were used in the heat exchanger to accomplish the jump from a standard to mid efficient furnace? What is the major drawback in employing these?

Answer 6

Thinner, metals with greater heat transfer capabilities, with a tubular design. There is a greater pressure drop through the heat exchanger and convection currents may not be relied upon to exhaust the gases; A combustion air blower must be used.

Question 7

The first device to operate on a mid/ high efficient furnace is?

Answer 7

The combustion air blower, performing a pre purge of the heat exchanger.

Question 8

There are two types of combustion air blowers, what are they and why are they different?

Answer 8

Induced draft fan (pulls air into heat exchanger and pushes it out the flue.)
Forced draft fan (pushes air into the heat exhanger and subsequently out the flue.)

The difference is entirely positioning.

Question 9

What is another name for a secondary heat exchanger?

Answer 9

Condenser coil.

Question 10

Is the maximum number of high limit switches in an efficient furnace 1?

Answer 10

No, often there is a second high limit at the back of the plenum and two flame rollout switches which are essentially high limits.

Question 11

What type of bimetallic sensing element is typically used for an efficient furnace high limit?

Answer 11

Disc type. (sometimes strip)

Question 12

Why is an air prove switch required?

Answer 12

So that we know fresh air is moving into the heat exchanger. (To avoid major explosions with undesirable gases.)

Question 13

What is a typical set point for a high limit?

Answer 13

Between 82 and 94 degrees C.

Question 14

What ignition method do most high efficiency furnaces use?

Answer 14

Hot surface igniter.

Question 15

How does a DSI ignite gas?

Answer 15

It sends a high potential (up to 5000V) arc across an air gap; This arc ignites the gas.

Question 16

What are three benefits of HSI over IP?

Answer 16

Reliable,
Eliminate the need for a pilot,
Inexpensive.

Question 17

What material is typically used in Hot surface igniters? How hot does it generally get when energized?

Answer 17

Silicon nitride. 1370 degrees C.

Question 18

Should an igniter typically shut down after the flame has been proven?

Answer 18

Yes.

Question 19

What is the common flame rectification current ratio?

Answer 19

4(out):1(return)

Question 20

What are some problems which could cause flame rollout?

Answer 20

Inadequate building static pressure,
Plugged or obstructed heat exchanger,
Misaligned burners,
Cracked burner tube / manifold,
Gas leak,
Dirty or faulty CAB, 
Cracked heat exchanger.

Question 21

How are modern IFM made more efficient?

Answer 21

They are directly coupled and contain a capacitor which allows for smooth quiet operation.

Question 22

What are the three main fan speeds used for?

Answer 22

Low - Continuous operation,
Mid - Heating,
High - Cooling.

Question 23

Could installing the wrong ECB cause a violent explosion?

Answer 23

Definitely, always install to spec.

Question 24

What temperature is the exhaust gas from a high efficient furnace?

Answer 24

Roughly 40 degrees C.

Question 25

What is the purpose of a dual stage burner?

Answer 25

To run the furnace on high or low depending on the required heating load.

Question 26

In Canada, is it acceptable to position a high efficient furnace’s exhaust vent in an outside wall, one foot above grade?

Answer 26

Yes.

Question 27

Do high efficiency furnaces require annual maintenance?

Answer 27

Yes.

Question 28

What kind of filter will eliminate particles up to one micron in size?

Answer 28

A high efficiency filter.

Question 29

What kind of filter will be used in an environment where the probability of mold and micro organisms is very high?

Answer 29

A micro-biocide treated filter.

Question 30

Do electrostatic filters require line voltage to operate?

Answer 30

No, they require no voltage.

Question 31

Could a dirty or plugged filter cause an AC compressor to fail?

Answer 31

Yes.

Question 32

What does EAC stand for, what must they be interlocked with, for operation?

Answer 32

Electronic air cleaner.

Interlocked with the Indoor Fan Motor. (This way they only draw energy when needed.

Question 33

What is a typical comfortable humidity and temperature for humans?

Answer 33

40% at 22 degrees C.

Question 34

What are the four common types of humidifier?

Answer 34

Standing water absorbent-pad,
Rotating drum, (Calcifies easily)
Rotating disc, (Probably the best)
Flow-through. (Wasteful)

Question 35

How many volts does a humidifier motor typically run on?

Answer 35

24.

Question 36

How many air exchanges per hour should the average home have?

Answer 36

0.35.

Question 37

When installing a main exhaust fan, what must it be interlocked with?

Answer 37

The blower fan (IFM) and an HRV (if equipped).