It seems like the most reasonable thing to do; turn off the AC system because your home is empty and no cooling is required. But, this may not be the best way to deal with this issue and it may even cause other problems and expenses. To keep your home safe and protect the AC system, it may be a better idea to manage the system. An alternative approach is to use a programmable or smart thermostat to set the temperature slightly higher.

Why Not Turn It Off?

There are two very good reasons why you may want to consider leaving the AC system on at a slightly higher temperature when you’re away on summer vacation. They are:

  • Protecting the Home: Many people are not aware that an air conditioner plays a role in the management of indoor humidity. Although it is not as efficient as a dedicated dehumidifier, it will prevent some of the issues caused by heat buildup and humidity. These are perfect conditions for rapid mold growth and mold spores can lower the indoor air quality (IAQ),
  • Returning to a Comfortable Home: When you return home, it can be uncomfortable for some time if you’re bringing the temperature down from a cold start. The AC system will also have to work much harder to make the indoor temperature comfortable. This can consume a lot of extra energy and it places the system under additional stress which can cause damage.

To use this technique efficiently you will need to invest in a programmable or smart thermostat.

Using and Programmable or Smart Thermostat

These thermostats have the programmability that’s needed to lower and raise the temperature for your departure and arrival. The smart thermostat is the ultimate upgrade because it’s possible to program the unit remotely in real time via a Wifi connection. So, while you’re away you can even monitor the AC system and make adjustments as needed to improve energy efficiency. The best examples usually have a dedicated vacation mode to make this process even easier.

Unfortunately, some older AC systems are not compatible with smart thermostats. Check with your local HVAC specialist to see if you can install a programmable or smart thermostat to use with your existing heating and cooling system.

How Do I Use This Technique?

The optimal empty home vacation temperature is around 85ºF which is 7-10ºF higher than it should be set when you’re at home. At this temperature, the air will continue to be circulated throughout the home which will prevent the spaces from becoming too hot. If you’re using a programmable thermostat, it can be set to be slightly cooler during the day and a little warmer at night. This will keep the indoor temperature pretty constant and save you some energy at the same time. If you’re using a smart thermostat you can make the changes on the fly with a smartphone or your favorite mobile device. So, you can adjust the indoor temperature to match changing weather conditions to make extra energy savings.

This is a wasteful technique to use if the treated air can escape outdoors. So, the house must be tightly sealed with locked doors and closed windows until you return from vacation. That said, there could be gaps around the doors and windows where the air can escape that you cannot see. To check for drafts, run a candle around the perimeter of the doors and windows and look for a flickering flame. If you find any drafts mark them with chalk or some other non-permanent marker. Any gaps in door frames can be fixed with weatherstripping and window gaps can be sealed with caulk.

When Should I Leave the AC System Off?

There are a few reasons why you may want to leave the AC system off when you leave for your summer vacation. They are:

  • The Vacation Length: This technique is a great option for shorter vacations from a weekend up to a week or two. But, if you’re going away for much longer it’s not a viable option and you may need to look at other solutions. A dehumidifier on a timer can keep the mold at bay and adding shade to rooms to keep the sunlight out can help keep the internal temperatures down. If you have adequate levels of insulation it is much easier to keep the indoor temperatures consistent.
  • The Weather: If the external temperatures are going to be mild, you can turn the AC system off. But, you will need to check the weather forecast carefully to ensure that you don’t get caught out by changing temperatures. This is less of an issue if you have a smart thermostat because you can adjust the thermostat remotely to compensate for temperature fluctuations.
  • Maximizing Energy Savings: If your primary reason for turning off the AC system is to save energy, you will want to turn the system off. This is especially true if you’re planning to be away for longer than a week.

In Conclusion

It’s important to understand that leaving the AC system on at a regular temperature will place extra strain on the components and waste a lot of energy. But, setting the thermostat to 7-10ºF higher with adjustments for daytime and night can be very effective. This is only possible with a programmable or smart thermostat. These offer a great value proposition because they can lower the cooling bills by 15-30%.

If you’re leaving the home with pets in the residence that will be on their own for most of the time, this is the perfect solution. Most pets will be comfortable at 79ºF or 80ºF, but they need plenty of clean and fresh drinking water to stay hydrated. Of course, they will get some company when the designated pet sitter turns up to feed them and top up their water bowls. At this time the sitter can evaluate how the home feels and let you know if an adjustment by them in-person or by you remotely is needed.

If you want to install a programmable or smart thermostat in your home, contact your local heating and cooling specialist.