Hello Robert,
I have mounted older versions of this device in friends and families panels. I assume you have a typ. 120/240 single phase service. Consider protecting both legs as close as practical to the main breaker, keeping the protector's leads as short as possible without sharp bends. You want to minimize lead inductance to the MOV and maximize it to everywhere else. Then, if you want to get sneaky and have enough length for your furnace hot, try winding a pigtail into it.(Like the neutral pigtail on a GFCI breaker.) This has no effect @ 120/60Hz but looks like a substantial reactance to a hi-f pulse. If you read the datasheet, you'll see that the clamping voltage on that arrestor is a couple of hundred volts more than you want your furnace to ever see!!! If I had one of those new-fangled electronic ignition furnaces, it would probably have magically grown at least one, 1.5KE130CA bi-directional, 130V RMS transient voltage suppressor, 1500Watt surge rating (TVS) I believe that they have faster transient responses than those red or black MOVs that you may have seen.(They look like fairly large disc capacitors.) So Robert, if you have the skills and replaced the control board yourself, You might be able to add this additional protection as well. Finally, always make sure you have proper overcurrent protection before surge protection!
Take care & be safe!
Joe
