A protector does not stop, block, or absorb destructive
surges. And yet lightning damage is routinely avoided; as Ben
Franklin even demonstrated in 1752. He also did not stop,
block, or absorb lightning as others even here suggest as a
solution.

Every incoming wire must earth surges before that wire can
enter the building. So simple, so effective, and so
inexpensive that your telco installs such a protector, for
free, where their wire connects to your building. Cable needs
no protector. A properly installed cable first drops down to
hardwire their ground block to your earth ground. Only then
does the cable rise back up to enter the building.

In your case, lightning may have found earth ground,
destructively, via a furnace. First lightning forms a
complete path from cloud to earth. Only items in that path -
that have both an incoming and an outgoing electrical
connection - would be damaged. No, lightning is not
capricious. It caused furnace damage for good, basic
electrical reasons. Other appliances were not a better path.

Protectors are not protection. The single point earth
ground is protection. Secondary protection is earth ground
connected to AC electric box. That means your building's
earth ground system must met and probably exceed post 1990
National Electrical Code (NEC).

To connect all three incoming AC electric wires to that
earth ground, you require a 'whole house' protector such as
are sold in Home Depot and Lowes. No effective protector has
been observed in Sears Hardware, Kmart, Walmart, Office Depot,
Radio Shack, Best Buy, Staples, or Circuit City. Effective
protectors have names of more responsible electrical
manufacturers such as Intermatic, Square D, GE, Siemens,
Polyphaser, Leviton, and Cutler Hammer. Effective protectors
make a short (less than 10 foot) connection to the single
point earth ground. Ineffective protectors forget to discuss
earthing.

Defined above is secondary protection. Also inspect your
primary protection system:
http://www.tvtower.com/fpl.html

Currently ongoing is a discussion about protection and
earthing in the rec.radio.shortwave newsgroup entitled
"grounding and surge".

All appliances contain protection that would work on the
power cord. Internal protection that can be overwhelmed if
destructive transients are not earthed before entering a
building. Shunt mode protectors that don't make a short
connection to earth simply forget to mention which type of
surges they protect from. They don't protect from typically
destructive transients. Obviously. Where is the 'less than
10 foot' connection to earth? So instead they forget to
discuss earth ground hoping you will instead use word
association: "surge protector = surge protection". The
assumption is false. Surge 'protection' is earth ground.
Effective surge 'protector' makes an earth ground connection
during the surge. But when a $3 power strip with some $0.10
components is sold for $15 or $50, why would they want you to
know the facts - and endanger such high profits?

A protector is only as effective as its earth ground. If
lightning damaged your furnace, the furnace was a destructive
path to earth ground. Install an earth ground path that is no
so destructive.

Robert11 wrote:
I recently had installed a new hot air furnace, that also has an
Evaporator section in it for the house air conditioning.

Last night, a thunder storm passed thru the area.
Nothing really major; have certainly seen worse.
A bit of lightning, etc.

Lights flickered for a few seconds.
This is the first time since the new installation that we had this
type of storm.

Anyway, the main circuit board in the furnace fried.

Surprisingly, nothing else in the house suffered any damage,
whatsoever. Even the PC's still work. Of course most of the other
items in the house are plugged into power extension strips with
overvoltage and spike protection; perhaps this saved them ? Hard
to know for sure, though.

The furnace (110 V) is, of course, hard wired to the house wiring via a
dedicated circuit breaker.

My question is:
Would really hate to have it happen again.

Is there any kind of circuit breaker we can change to that has this
spike and overvoltage protection ?