I've gotten a lot of help here in making the decision what type of system to put in a new house. I've pretty much made up my mind except for one big issue, and that is zoning.
Zoning is attractive to me as a concept. The zoned system allows me to afford a higher efficiency unit than I might have if I had 2 units, and the concept of shutting off unused zones seems like it might be an energy saver. It also seems as though VS and zoning could be a good match. My local Trane dealer (who I have worked with from the beginning) is about the only local dealer who is enthusiastic about zoning. His son has a Trane zoned system and he is so impressed with the zoned system that he is installing a new zoned system in his house later this year in conjunction with a room addition.
I have called several other dealers who sell other brands I was interested in but they have never done a zoned system. (Another interesting experience I have had is that in a town of over 450,000 the only Lennox dealer does not do new residential construction and 2 of 3 Rheem/Ruud dealers also expressed no interest in new residential construction or zoning. There are, however, about 15 York dealers in my town).
So here's my issue: The architect's load calculation calls for 2 split system units totaling 6.5 tons. The house is 3139 sq ft in Bakersfield, CA (hot dry summers and mild winters). I have asked for but have not yet received a copy of the load calcs. Previous responses on this site have questioned that much cooling for 3139 sq ft for a new home built to Title 24 specs.
Aside from issues of whether the load calc is correct, does using a zoned system allow you to change to size of the units? My guess is no, in that whether you are using 1 or 2 systems the house's demands remain the same.
The reason I ask is that the dealer mentioned above has quoted me a 5 ton single system (Trane XL19 and XV90) used in conjunction with the zoned system (3 zones). He is confident that the system will handle the demands of the house. If a properly prepared Manual J shows 6.5 tons then would it prudent for me to have a 5 ton zoned system?
The Trane dealer told me he has never had county building inspector question a smaller zoned unit when the plans called for more capacity. I am worried that a building inspector would challenge my 5 ton unit when the plans called for 6.5 tons.
Have you ever done a zoned system that had less capacity than a 2 unit set up? What issues or concerns should I have and what questions should I pose to my dealer? Is it the HVAC contractor's responsibility ot insure that the system meets local code requirements? I am building the house with a construction manager without a general contractor, so I want to make sure I don't have an inspection problem.
One last zoning issue having to do with IAQ. With 2 units I was going to go with 2 Aprilaire 2200 filters. With a zoned system I will only have 1 filter. Is this a problem (more frequent filter changes, etc.)?
Thanks very much.