Deciding between “2 A/C units or 1” is a dilemma many two-story homeowners find themselves facing at some point. Having just one is not always efficient. Crank up the thermostat and it gets too cold downstairs. Put it at a temperature that makes it comfy downstairs and the upstairs area can become a furnace. There are two alternatives to this up and down process: Installing 2 A/C units and installing a zoned system.



There are some advantages to having two air conditioner units in your two-story home versus having just one. Yet, there are certain cases when this isn’t the best choice. Whether it’s best to run a second A/C unit or install a zoned system depends on the design and age of your house.

Balancing the Temperature

When it comes to older homes, it can be pretty rough keeping the same temperature throughout the whole house. And, since heat rises, the second floor is generally much hotter than the first floor. So, in order to get one floor to a comfortable temperature, the other floor will often end up being too cold or too hot. Installing two central air conditioner units allows you to have one on each floor. That way, you can maintain comfortable temperature on both floors.

Costs of 2 A/C Units Versus 1

The cost of buying two central a/c units may be initially more expensive than buying one, of course. But, for two-story homes, the cost of trying to cool your entire home on one unit could be even more expensive, as far as your monthly energy costs are concerned. The only other effective alternative is to buy one large unit, powerful enough to cool the upstairs as well as the downstairs areas.

Overall Energy Costs

Having one, non-zoned A/C unit means cooling all the areas of the home, even those not being used at the time. The method generally works like this: During the day, the first floor is cooled down. Then, at night, the a/c is turned off, if the coolness remained inside. If not, (such as windows were opened, letting hot air in), the unit needs to be turned on to keep the upstairs area cool. This process can be pretty expensive. A more cost-efficient solutions would be to have one unit upstairs and one downstairs. Another option is to go with a zoned a/c unit.

Unit Failure

One of the great benefits of having to A/C units is that one can act as a backup if there’s a system failure. There’s a good possibility that one will keep your home reasonably comfortable while the other undergoes repairs. However, there’s also the possibility of both failing at the same time. This could be extremely costly to fix if it happens.


What is a zoned system? It’s an A/C system that allows you to install multiple thermostats and use them to control one central A/C unit. Zoned systems come with dampers that are installed within the system’s ductwork. These dampers close and open, as needed, in order to regulate air flow in each of the zones. This allows you to regulate each zone’s specific temperature.

How is a zoned system more beneficial than having two central A/C units? Well, let’s say your downstairs area and upstairs area are your two zones. Each one can be closed off, turned up or turned down. Each zone also has its own thermostat. So, you have full control over “zoning” the comfortable temperature of each area.