Is it always necessary to have 2 zones when installing central air?

Question

I just had an estimate done and I was quoted a price based on 1 zone. The contractor told me that my house did not need 2 zones. I thought all houses needed at least 2 zones.

Answer 1

As a veteran of the installation of many zoned systems, my gut tells me to keep things as simple as possible. A "zoned" system means many different things, so I am assuming you are talking about having the capacity to shut down a sector of your home via a thermostat.

The alleged savings from this technique never materializes. It is important to keep cool, dehydrated air circulating throughout the entire home for several reasons. Let's assume the downstairs gets shut off at night, and all cooling is taking place upstairs in the bedrooms. The heat and humidity continues to eminate upstairs from the unconditioned space and increases the load on the active zone. In the morning, you crank on the downstairs zone, and it labors (at increased cost) to rid the area of the latent heat (humidity) that has accumulated during the off-cycle. Meanwhile, the warm, moist environment is greatly appreciated by mold and bacteria that tend to grow prolifically in relative humidity exceeding 70%.

The latest technology features conditioning the entire home and gaining savings by virtue of variable speed blower motors and compressors. Your best investment is to bypass the zone technology, and purchase super-high efficiancy equipment to achieve your savings. Good luck!

Answer 2

Every house that I have lived in (3) has required forcing more air to the second floor ( with a "valve" in duct)because it is 5 to 10 degrees warmer than the first floor. I beleive this is commonly referred to as balancing the system. It is strictly a trial and error procedure. So, because of this having a zone for each floor makes alot of sense to me. I don't know if it would be more economical but I would think it would work alot better.