Take a look at the thermostat in your house and see how low it can be set. It’s probably 60°F, the standard for thermostats. That’s uncomfortably cool for most occasions, but it does make it sound like your air conditioner is powerful enough to always be able to lower your home’s indoor temperature that far. No matter how hot it gets outside, you can always have your home feel extra cool.
Except that’s not how an air conditioner works. There are limits on how much cooling an AC can provide a house, and in this post we’re going to look at what it is. You can use this information to help you find the right settings for your thermostat during summer.
The Temperature Differential of an Air Conditioner
An air conditioner isn’t just limited by the lowest setting on the thermostat. That setting tells the air conditioner when to shut off, but it doesn’t mean the air conditioner can actually reach that lower temperature. The AC has another limitation, which is its temperature differential.
This is an HVAC industry term for how much an air conditioning system can change the temperature of the incoming air. Another way to think of it is how much lower the AC can make the temperature inside a house compared to the outdoor temperature. Although commercial and industrial ACs may have higher temperature differentials, for a residential central AC the temperature differential is 20°F. So you can expect to have, at maximum, a home that’s 20°F cooler than the outside temperature (although there are other factors involved in cooling a house, such as the insulation that keeps heat out).
Using the Temperature Differential When Cooling Your Home
Imagine a standard warm summer day with an outdoor temperature of 88°F. How cool can the AC make your home? It can get it down to 68°F, which is enough for most people to feel cool. It might even be too cool since the energy-saving thermostat setting the US Department of Energy recommends is 78°F. When you keep the thermostat set at 78°F during the day when people are home, the AC can easily manage outdoor temperatures up to 98°F. (As we mentioned before, good insulation in a home will make it easier to handle the heat.)
When a serious heatwave strikes and the outdoor temperature rises above 100°F, we recommend you nudge up the thermostat to around 80°F. Don’t lower it more in reaction to the heat. This is a common mistake. The AC won’t give you more cool air or perform faster. Because of the temperature differential, it will keep running and running as it tries to reach a temperature that’s out of its range. That means huge electrical bills for no actual benefit, and it puts the AC at a higher danger of overheating and breaking down.