Don't you want to installed it way, way upstream where the breaker panel is? That would protect your house wiring insulation as well. With lightning where the transient is in the nano second range (super fast) anything could happen and surge protection is not 100% guarantee. Transient will seek a path to you furnace circuit board, or anything else, in the most unpredictable manner in a worst case scenario. In any case, make sure you have a good house ground, circuit board ground plane is solidly grounded and disconnect the main breaker during the next big lighting storm if you could.