________ are, essentially, temperature-actuated switches
Thermostats
Name the three types of most commonly used residential thermostats
Line-voltage, low-voltage, and electronic
________ thermostats act as on/off switches to conduct full power to the heater
Line-voltage
________ thermostats are used primarily for high-amperage electric heating systems
Low-voltage
________ thermostats are low-voltage and use semiconductor components for both temperature sensing and control-circuit switching
Electronic
Regardless of type, room thermostats should be mounted approximately ________ from the floor
1.5m (5ft)
What is the usual “watts per unit length” rating of standard density baseboard heaters?
250W/ft
Where in a room should baseboard heaters be mounted?
At floor level, centred along walls, and near areas of high heat loss (such as under windows)
What type of heater is normally installed at ceiling height?
Unit heaters
Residential electric furnaces are usually available in both single-phase and three-phase ratings from ________ kW to ________ kW
4, 50
What type of electric heater can be used with certain oil-fired, forced-air furnaces?
Plenum heaters
List two applications for heating cable sets
Radiant space heating (floor or ceiling), driveway/sidewalk ice melting, and freeze protection on pipes
Residential water heaters are commonly available in ________ kW and ________ ratings
3, 4.5
What are the three types of thermostats commonly used in residential space heating application?
Line-voltage, low-voltage, and electronic
Where are the supply registers of a forced-air furnace normally located?
Around the perimeter of each room, preferably in front of areas of high heat loss
What is the purpose of the heat exchanger in a gas-fired furnace?
To separate the products of combustion from the circulated air
A gas-fired furnace is typically ________ efficient
70-80%
How many conductors are commonly needed between the furnace and the room thermostat? What is the magnitude o the voltage that they carry?
Two or three, 24V
After the thermostat contacts open, which shuts off first, the blower motor or the gas burner?
The gas burner
What is the purpose of the anticipator resistor in the room thermostat?
To limit the set-point overshoot to an acceptable value
What is the purpose of the thermocouple? Is one always required?
When heated, the thermocouple generates a small current that holds the gas safety value open. A thermocouple is not required on units equipped with electronic spark ignition
List two conditions that may cause overheating of the heat exchanger
Rom thermostat contacts stuck closed, blower does not run, and insufficient air flow
Where should an electronic air cleaner be installed on a furnace?
In the return air duct, preferably downstream of the standard filter
Name the two classifications of fans
Centrifugal and axial
