Dual (elec and wood) furnaces. Route air ducting in series or parallel? Any preferences?
 

My contuinuing saga on the wood furnace is now this: my hvac buddy says
I should install in series, having the hot air from the wood furnace
(which has a blower) feed into the cold air return of the existing
electric furnace. Also to re-route the cold air return from the
electric into the wood furnace.

Does anyone have any opinions on this compared to doing it in parallel?

Thanks!

Dean