What Temperature To Leave A Vacant House In Summer? (Careful)

Should you turn off the air conditioner while going on a vacation? Absolutely not, and we will explain why. What it’s quite useful to know is what temperature to leave a vacant house in summer. We are talking about the constant thermostat setting for vacant houses in the summer.

Here is how we generally think about using AC in vacant homes:

“If I’m not living there, why would I spend $100s on running an air conditioner?”

Well, every HVAC expert will tell you that you are doing that in order to avoid $1,000s on needless house damages.

What Temperature To Leave A Vacant House In Summer
If you save on AC costs in your vacation house, you are probably doing a big mistake. The value of the house (and its integrity) outweighs the costs of AC every time.

Before we check out what temperature is best when you leave a vacant a house in summer, let’s explain why it does make sense to leave AC on when you leave your home:

Should Air Conditioner Be Left On In Vacant House?

Leaving AC on in a vacant house seems a bit unnecessarily (at first). We all know that running an air conditioner can cost quite a lot of money, especially during the hot summer months.

Now, what we need to understand is that houses (walls) and things in houses (wood, wallpapers, appliances) don’t really handle well two things:

  1. High temperature. At high temperatures, everything is happening quicker. That includes everything from the decay of furniture to wood warping and so on. Example: Wallpapers will more likely peel at higher temperatures, and the glue will also be affected.
  2. High relative humidity levels. High moisture levels will increase the penetration power of hot air. At 60% relative humidity levels or higher, the air carries a lot more heat. That heat can be used to make damage around your house.

The worst season is when these two harmful factors are combined: that’s the summer. In summer, we experience both high temperatures and high humidity levels.

If we don’t handle both of those a bit, we are exposing our house to harmful natural processes that are now happening a lot quicker. The longer the high temperature and humidity levels persist, the more damage they will incur.

Luckily, we do have a single device that can handle both of these issues. Modern air conditioners are designed both to:

  1. Lower temperature. We will talk about exactly what temperature we should set the thermostat in vacant houses.
  2. Lower humidity levels. 60% moisture levels and above can damage our house. EPA recommends setting humidistat settings to between 30% and 50% in order to avoid damage and avoid potential mold growth (which can, in turn, cause further damage).

Humidity-wise, it makes sense to set your humidistats to 40% when you leave a vacant home in summer. There is a bit more discussion about is the best temperature to leave a vacant house in summer:

Best Temperature To Leave A Vacant House At In Summer?

Alright, once you understand that running an AC is a must even in vacant homes, you will probably want to know what temperature to leave a vacant house in summer. Sadly, there is not much consensus about the exact temperature.

Here is the compromise we are making:

AC running costs vs. house damages.

Now, we can estimate AC running costs quite easily. Here is the full article about how much does it take to run an air conditioner in the summer; you can consult it just to see that we can measure that. For example, elevating your AC thermostat setting by 1-degree will reduce the running costs by about 3%. Using this premise, an 85°F setting in a vacant house will cut the air conditioning costs by 28% if you compare it with a 78°F setting.

Should Air Conditioner Be Left On In Vacant House
Lower thermostat setting will increase AC running costs but will help you protect your house.

But how much will house damages increase due to higher temperature in a vacant house in summer?

Nobody really knows. The problem with getting this compromise right is that it is very difficult (nearly impossible) to estimate the damages to your house if you increase the temperature in a vacant house by 1 degree, for example.

That’s why we have different recommendations about exactly what is the best temperature to leave a vacant house in May, June, July, and August. Here are some temperatures that are being thrown around:

  • “When you leave home, set your temperature to 72°F.” This is a very AC-heavy recommendation. It might be that you will unnecessarily increase the air conditioning costs a bit too much.
  • “When you leave home, set your temperature to 78°F.” This seems like a good compromise between lowering air conditioning costs and keeping your house (and everything in it) a bit safer from the high temperature-humidity combo.
  • “When you leave home, set your temperature to 85°F.” This seems like a bit of dangerous advice. Keeping a house at such a high temperature might exacerbate the damages quickly (especially at high humidity levels).

As you can see, we:

  • Do know AC needs to be running in a vacant house in the summer.
  • Don’t know the exact temperature setting that would be the best compromise between AC costs and house damages.

In lieu of a scientifically calculated exact temperature, some people ask us this:

“Alright, when you leave a house vacant, what temperature do YOU set the thermostat at?”

This is quite a useful question. When we leave a house, we usually set the temperature to 78°F in high summer (due to high humidity). If the humidity is not all that high (May, August, September) we might turn the temperature up to 80°F but not higher.

Hope you find this at least a little bit helpful and that you now understand why it is better to leave an AC on in a vacant house.

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