This article is an effort to define the ideal indoor humidity, which is a necessarily debatable figure due to multiple variables and the subjectivity of comfort. However, it does help to look at general comfort ranges. We include a chart of the relationship between humidity and comfort, as well as an infographic of humidity levels information.
Do you want to get an understanding of how your humidity level relates to how comfortable the environment is? There are more and less specific ways to discuss this subject. One general way to understand humidity’s impact on comfort is the “30 to 50 percent rule.” Another is the ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) standards. You can also get a sense of “feels like” temperatures and consider comfortable temperature-humidity combinations with a humidity levels chart.
Before we get into any of the efforts to guide comfort and home humidity levels chart, though, we need to have an understanding of different forms of humidity and temperature.
The first step toward your ideal indoor humidity is to find out your humidity levels using a hygrometer, in humidity mode.
The notion of relative humidity is important to understanding comfort related to humidity levels. We can get a better sense of relative humidity by considering absolute humidity.
Now that we understand these different forms of humidity, let’s look at three forms of temperature: dry bulb temperature, wet bulb temperature, and dew point temperature.
Safe humidity levels create an environment that is more comfortable as well as healthier. You want your home’s humidity to be between 30 percent and 50 percent, according to BobVila.com. People whose home humidity levels are maintained between 30% and 50% (the safe indoor humidity level from the Environmental Protection Agency) will become sick less often and get higher-quality sleep.
Why are these considered the best humidity levels? The reason has to do with what goes wrong when humidity is outside this range.
It is critical that humidity not be lower than 30 percent because of the following issues:
In extreme low humidity, 5 percent or below, building materials and wood furniture may shrink, eventually cracking or warping. Wallpaper will often start peeling off the wall, too.
Similarly, it is important that humidity not be higher than 50 percent, for four primary reasons:
The best humidity levels are not necessarily in that range, though. What is considered comfortable humidity is often discussed as ten degrees higher.
The ASHRAE Standards indicate the following ideal range of comfortable temperatures for home humidity levels in the 40 to 60% range, based on the season:
This chart is based on a chart called “Indoor Comfort equivalent Temperature and Humidity Table,” from National Comfort Institute (HVAC training company) President Rob Falke.
Keep in mind as you look at these numbers that they cannot be accurate for every individual. There are other factors influencing the comfort of a person at a certain humidity: their age, for instance.
The summer comfort range is highlighted in green, and the winter comfort range is highlighted in blue. Notice how these numbers do not directly follow the ASHRAE Standards but are close to them.
Chart of Equivalent “Feels Like” Indoor Temperatures at 6 Relative Humidity Levels
| Room dry bulb temperature | 30% RH | 40% RH | 50% RH | 60% RH | 70% RH | 80% RH |
| 62 | 62 | 63 | 64 | 64.5 | 65 | 66 |
| 63 | 63 | 64 | 65 | 65.5 | 66 | 67 |
| 64 | 64 | 65 | 65.5 | 66 | 67 | 67.5 |
| 65 | 65 | 66 | 67 | 67.5 | 68 | 69 |
| 65 | 66 | 66.5 | 67.5 | 68 | 69 | 70 |
| 66 | 66.5 | 67.5 | 68 | 69 | 70 | 71 |
| 68 | 67.5 | 68.5 | 69.5 | 70 | 71 | 72 |
| 68 | 68 | 69 | 70 | 71 | 72 | 73 |
| 69 | 69 | 70 | 70.5 | 71.5 | 72.5 | 73.5 |
| 69 | 69.5 | 70.5 | 71.5 | 72.5 | 73.5 | 74.5 |
| 70 | 70.5 | 71.5 | 73 | 74 | 75 | 76 |
| 71 | 71.5 | 73 | 74 | 75 | 76 | 77.5 |
| 72 | 72 | 73.5 | 75 | 76 | 77 | 78 |
| 73 | 73 | 74 | 75.5 | 77 | 78 | 79 |
| 74 | 74 | 75 | 76 | 77.5 | 79 | 80 |
| 75 | 75 | 76 | 77 | 78 | 79.5 | 81 |
| 76 | 76 | 77 | 78 | 79 | 80 | 82.5 |
| 77 | 77 | 78 | 79 | 80 | 81.5 | 83 |
| 78 | 78 | 79 | 80 | 81.5 | 83 | 84 |
| 79 | 79 | 80 | 81.5 | 83 | 84 | 85 |
| 80 | 80 | 81.5 | 83 | 84 | 85 | 86 |
People often think that air conditioners can basically run until they collapse. However, letting a reasonable replacement period elapse, going beyond that expected effective period (or forecasted useful life) of an HVAC system can mean that its parts begin to degrade. As the system ages, it becomes less able to remove humidity from the air. The expected useful life for air conditioning window units is 8 to 10 years, while the same for a central AC system is 12 to 15 years, again per BobVila.com.
Even if you decide you just need maintenance, you can save money by getting your HVAC system maintained during the summer.