An internal heat exchanger has only one wall that separates two liquids.

Commercial and industrial units typically operate between 208 V and 440 V.

Only high-input commercial heaters utilize a multiple-flue construction design.

A passive system does not require a pump to circulate heat transfer fluid.

A pressure-reducing valve normally is set to activate when pressures within a tank exceed 100 psi (689.5 kPa).

Protection against vacuum conditions within a water heater is required by both model plumbing codes.

Sunburn is a good example of a second-degree burn.

The most commonly used types of insulation for hot water piping is fibrous glass and flexible tubing insulation.

Gravity circulation is the circulation of water based on the use of a mechanical pump.

In the 2018 UPC, ___ water is water at a temperature higher than or equal to 120°F (49°C).

A common problem with water-jacketed back heating systems was ___.

An increase in the volume of water produced by thermal expansion creates a corresponding rise in ___.

The coefficient of thermal expansion is the unit increase or decrease in the length of a material per ___°F increase or decrease in temperature.

A(n) ___ is a device or piping arrangement incorporated into the discharge piping of a storage-type water heater or hot water storage tank to prevent the gravity circulation of heated water into outlet piping.

A(n) ___ heating element is a heating device that makes direct contact with the substance to be heated.

A(n) ___is a passage within an appliance through which combustion products pass from the combustion chamber of the appliance to the draft hood inlet opening on an appliance equipped with a draft hood or to the appliance outlet on an appliance not equipped with a draft hood.

___ systems use pumps to circulate a heat transfer fluid through a solar collector and heat exchanger system.

A(n) ___ water heater is a nonstorage water heater that heats and dispenses water at the point of use.

Relief valves should be tested ___.

The American Society of Plumbing Engineers (ASPE) recommends that the outlet temperature at a storage-type water heater be between ___ to prevent the growth of Legionella bacteria normally present in the water.

A ___ is an adjustable and lockable means to limit the maximum hot-position setting of a device.

The 2018 IPC requires that piping be less than 1" to have a minimum insulation wall thickness of ___".

A ___ circulation system is a forced DHW circulation system that utilizes a circulator to draw water from the hot water fixture supply and push it through the cold water fixture supply.

A(n) ___ was a system utilizing a raised floor set on stacks of tiles called pilae.

The ___ temperature and pressure relief valve had a lead plug that melted when the water temperature reached 210°F (99°C).

___ is a natural process of convection in which layers of water form based on temperature.

A(n) ___ heat exchanger resides in a water heating storage tank and allows the transfer of heat from an HTF to the potable water without the two liquids mixing.

Water heaters can be classified in categories based on storage capability, ___, and use in residential or commercial/industrial buildings.

A(n) ___ control circuit keeps water near a set temperature by controlling the firing and extinguishing of the main burner.

A(n) ___ flue is a single flue that passes through a water heater tank from the bottom to the top.

___ collectors are the most common type of solar energy collectors installed in domestic water heater applications.

Superheated water is water under pressure that is heated above ___°F without becoming steam.

___ is an injury caused by exposure to hot water.

The primary objective of a DHW system is to safely provide ___ to fixtures and appliances at a predetermined temperature.

___ is an electrical heating element embedded in flexible cable that runs along the length of piping and activates when the pipe temperature drops below a predetermined set point.