Efficient Gas-Fired, Forced-Air Heating systems Flashcards

1
Q

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

A

80-83%.

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2
Q

What does AFUE stand for?

A

Annual Fuel Utilization Efficiency.

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3
Q

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

A

90%

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4
Q

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

A

Carbonic Acid. (condensed water and carbon dioxide gases)

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5
Q

Can you run a high efficient flue horizontally?

A

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.

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6
Q

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?

A

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.

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7
Q

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

A

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

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8
Q

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

A

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.

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9
Q

What is another name for a secondary heat exchanger?

A

Condenser coil.

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10
Q

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

A

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

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11
Q

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

A

Disc type. (sometimes strip)

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12
Q

Why is an air prove switch required?

A

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

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13
Q

What is a typical set point for a high limit?

A

Between 82 and 94 degrees C.

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14
Q

What ignition method do most high efficiency furnaces use?

A

Hot surface igniter.

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15
Q

How does a DSI ignite gas?

A

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

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16
Q

What are three benefits of HSI over IP?

A

Reliable,
Eliminate the need for a pilot,
Inexpensive.

17
Q

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

A

Silicon nitride. 1370 degrees C.

18
Q

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

A

Yes.

19
Q

What is the common flame rectification current ratio?

A

4(out):1(return)

20
Q

What are some problems which could cause flame rollout?

A
Inadequate building static pressure,
Plugged or obstructed heat exchanger,
Misaligned burners,
Cracked burner tube / manifold,
Gas leak,
Dirty or faulty CAB, 
Cracked heat exchanger.
21
Q

How are modern IFM made more efficient?

A

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

22
Q

What are the three main fan speeds used for?

A

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

23
Q

Could installing the wrong ECB cause a violent explosion?

A

Definitely, always install to spec.

24
Q

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

A

Roughly 40 degrees C.

25
Q

What is the purpose of a dual stage burner?

A

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

26
Q

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

A

Yes.

27
Q

Do high efficiency furnaces require annual maintenance?

A

Yes.

28
Q

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

A

A high efficiency filter.

29
Q

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

A

A micro-biocide treated filter.

30
Q

Do electrostatic filters require line voltage to operate?

A

No, they require no voltage.

31
Q

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

A

Yes.

32
Q

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

A

Electronic air cleaner.

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

33
Q

What is a typical comfortable humidity and temperature for humans?

A

40% at 22 degrees C.

34
Q

What are the four common types of humidifier?

A

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

35
Q

How many volts does a humidifier motor typically run on?

A

24.

36
Q

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

A

0.35.

37
Q

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

A

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