I have a 2 story ~ 2700 sqft "colonial" style house built in 2004. It's heated via forced air (oil burner) with A/C. The house was built as 2 zones (1st floor/2nd floor) with an unfinished basement which houses mechanicals (water treatment, furnace, air handler, most of the ductwork, etc).
I am in the process of finishing off the basement into 2 parts - mechanicals and storage (unheated/uncooled), about 1/3 of the floorspace, and the remainder a living space with insulated walls, fully finished, etc. I have never had any water or condensation issues in the basement. The house does have a french drain-type system but I've never heard the sump go on.
At any rate, the zones are controlled via dampers and an EWC zone controller. While trying to debug a fritzy AC compressor (turned out to be a mouse that cooked itself in the contactor), I became very familiar with the logic of the zone controller and associated tstat wiring.
I'd like to extend the HVAC to the new basement space, and this should be quite easy given that the overhead is exposed, so ductwork should be a cinch to run. The issues come in in adding another zone - this requires another damper, but also would require a daughter board off the EWC to extend it past 2 zones. Now this is starting to get expensive and out of my comfort range for such things.
Then I thought - I could run the basement off the 1st floor control (e.g. just add vents/returns in the basement) or even better, add a tstat in parallel with the 1st floor tstat.
I do understand that there will be tradeoffs with this - just as if the whole house was ducted with a single zone, the only accurate temperature zone would be the one in which the tstat sits, with other areas being hotter or colder depending upon where ducts and such are located. By parallel wiring a tstat, theoretically, for example when in heat mode, you'd be assured that each zone is at least as hot as it's supposed to be. As is, I have a wood stove on the 1st floor, so while the tstat may be set at 65, most of the time it's in the 70's.
Again I understand the tradeoffs, but is there an equipment durability issue with wiring it this way? e.g. will it affect the longevity of the furnace or AC?