First, it does now matter whether that circuit breaker
protector is on a furnace circuit or installed as a 20 amp
breaker for another circuit (on the same phase). Either
provides the same transient protection to that furnace. Or as
that Siemens app note says, "An electrical surge, whether it
is caused by electrical equipment or lightning, always seeks
ground. Any component between the source of the surge and
ground can be damaged."

IOW the protector inside that Siemens circuit breaker
connects as if just another light bulb - connects in parallel
- is not electrically located between a lightning cloud and
the furnace. The protector does not stop or block surges. It
shunts.

Second, protector is not the open contacts of a circuit
breaker. That would be (futilely) stopping or blocking
transients. A 'whole house' protector inside that breaker
protects by 'shunting' a surge to earth ground. IOW the
internal protector operates independently of the circuit
breaker.

They are called shunt mode protectors. This Siemens breaker
installed on any circuit (of same phase) protects the
furnace. Protector inside that circuit breaker shunts the
transient to earth ground - whether it is a 15 amp furnace
circuit breaker or any other (same phase) 20 amp breaker.

The Siemens breaker (like all shunt mode protectors) does
not stop, block, or absorb surges. It shunts. It must have a
single point earth ground to shunt to. That means earthing
may need be upgraded to meet or exceed post 1990 NEC
requirements.

Third, the effectiveness of a protector during one transient
is determined by quality of that earth ground.

Effectiveness of a protector over many transients is
determined by its joules rating. A protector shunts - just
like a wire. More joules means 'the wire' is thicker. Any
protector that fails during a first transient was woefully
undersized - totally ineffective - too few joules - just like
so many plug-in protectors. An effective protector shunts
direct lightning strikes to earth and remains functional.
Joules and amps numbers determine protector's life
expectancy. Install two such Siemens breakers in the circuit
box (to double the number of joules); life expectancy of both
breakers increases exponentially.

For residential 'whole house' protectors, minimally
sufficient is 1000 joules and 50,000 amps. Does not matter
whether it is a "surge protector" or a "transient voltage
surge protector". Joules determine protector's life
expectancy. Earth ground determines its single transient
effectiveness.

Fourth, the Siemens solution has one difference over other
'whole house' protectors. Once a protector has failed, then
that circuit cannot be reset; circuit breaker must be
replaced. The circuit breaker trips long after a transient
has come and gone. For example, 300 consecutive transients
could come and go before the circuit breaker trips. The
circuit breaker is not protection. But once the internal
protector has failed, then a Siemens breaker will no long
provide power to the furnace.

Fifth, there is no 'functional' difference between TVSS and
surge protectors. Both are only as effective as their earth
ground, as the Siemens app note even suggests. Most critical
is the quality of that single point ground AND how wire to
that earth ground is routed. For example, sharp wire bends
mean a compromised protector. Ground wire bundled with other
wires may induce transients on those other wires. And so to
summarize it: a protector is only as effective as its earth
ground.

Earth ground determines a protector's effectiveness during
one transient. Joules determines the protector's life
expectancy. The difference between TVSS and surge protector
is irrelevant. Your concern is two important parameters -
joules and how the protector is earthed.

Robert11 wrote:
Will probably be replacing a standard house circuit breaker with a
surge protector circuit breaker to provide protection for a furnace
board that seems to be pretty succeptible to lightning strikes
(please see my previous post).

The furnace runs off a dedicated 15 amp line, protected by its own
breaker in the main house panel.

Apparently they come in two flavors.

One being the standard "surge protector," and the other type a
"transient voltage surge protector".

They both seem to be available incorporated into 15 amp circuit
breakers that fit in the main house panel box.

Which do I probably want ?

Why ? What are the differences re protection, etc. ?