Contents (Click To Jump)
- 1 How Are Indoor Humidity And Temperatures Related?
- 2 What Is The Ideal Temperature and Humidity Level For Home?
- 3 What Are The Causes of Indoor Humidity Variations
- 4 What Are The Effects of High Humidity Levels?
- 5 What Happens When The Humidity Is Lower Than Recommended?
- 6 Some Tips For Lowering And Raising Humidity Levels At Home?
How Are Indoor Humidity And Temperatures Related?
When most homeowners turn on their furnace in the winter or air conditioner in the summer, they usually only think about the ideal temperature of their home. However, the humidity levels in your home are just as crucial to your comfort.
The reason most homeowners don’t concern themselves with humidity is because most thermostats don’t measure it. Therefore, without a baseline, why would it matter to them? The fact is it does matter, and it depends on the temperature.
Humidity and temperature are bound together, performing an intricate dance as your HVAC system heats and cools your home.
This is because the temperature of the air affects how much moisture it can hold. Warmer air can hold more moisture than colder air. The amount of water vapor air can hold at a given temperature is relative humidity.
Relative humidity (RH) is the percentage of the water vapor in the air at a given temperature. It changes when the temperature of the air increases or decreases. When the air temperature goes up, it can suspend more water molecules.
The reason relative humidity is called “relative” is that the moisture content is relative to the temperature of the air. Dew point is the temperature of the air when it cools to a point where it saturates with water vapor (known as the dew point temperature).
It’s worth noting that absolute humidity is the actual amount of water suspended in the air regardless of the temperature (it’s measured in grams of water vapor per cubic meter of air). It is rarely used as a measure of humidity in homes.
Here is how relative humidity works (assuming you are not humidifying or dehumidifying the air):
- When the air temperature gets warmer, RH decreases
- When the air temperature gets cooler, RH increases
When you heat your home, you’re decreasing the RH as well. This is why you may find it insufferably dry in your home during the coldest days of winter. Here is how the outdoor RH and outdoor temperature range compare to the indoor RH after heating.
|Outdoor RH||Indoor RH at Below Outdoor Temperature|
|100% RH||2% RH||3% RH||6% RH||9% RH||14% RH||21% RH|
|90% RH||2% RH||2% RH||5% RH||8% RH||12% RH||19% RH|
|80% RH||2% RH||2% RH||5% RH||7% RH||11% RH||17% RH|
|70% RH||1% RH||2% RH||4% RH||6% RH||10% RH||15% RH|
|60% RH||1% RH||2% RH||3% RH||5% RH||8% RH||13% RH|
|50% RH||1% RH||1% RH||3% RH||4% RH||7% RH||10% RH|
|40% RH||1% RH||1% RH||2% RH||4% RH||6% RH||8% RH|
|30% RH||1% RH||1% RH||2% RH||3% RH||4% RH||6% RH|
|20% RH||0% RH||1% RH||1% RH||2% RH||3% RH||4% RH|
|10% RH||0% RH||0% RH||1% RH||1% RH||1% RH||2% RH|
|0% RH||0% RH||0% RH||0% RH||0% RH||0% RH||0% RH|
For example, if the humidity and temperature outdoors are 70% RH and 20º Fahrenheit, then the indoor RH will be 10% RH (as shown in the relative humidity chart above). An indoor humidity of only 10% is very dry and is less than ideal. However, if the temperature rises and the outdoor RH decreases, it could result in lower humidity in your home.
What Is The Ideal Temperature and Humidity Level For Home?
Since temperature and relative humidity are correlated, you might be wondering what the ideal temperature and RH levels are for your home. After all, you want your home as comfortable as possible and just adjusting the temperature isn’t enough.
To maximize the comfort and air quality in your home, ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) recommends an indoor relative humidity of 40% to 60% RH.
If the relative humidity drops below 40% or rises above 60%, your health and home may be negatively affected.
Getting a hygrometer to measure the wet bulb temperature, dry bulb temperature, relative humidity, and other air properties in your home will help you understand if you need to make changes to your home’s humidity.
What Are The Causes of Indoor Humidity Variations
Various factors affect the indoor humidity levels in your home. They include the outdoor temperature and humidity levels along with other sources of moisture in your home.
Outdoor Temperature and Humidity
The outdoor temperature impacts the amount of moisture in the air (the humidity). And since warmer air holds more moisture than cooler air, a temperature change will impact your indoor air’s humidity as well.
The air in your home doesn’t appear out of nowhere; it all comes from the outdoors and brings its moisture content along with it.
If the outside air is hot, your AC unit will lower its temperature and remove humidity from the air. The humidity condenses into water on your evaporator coils and drains through the condensate drain line to the outdoors.
On the other hand, if the outdoor air is very cold, your furnace will warm the air, and its relative humidity will lower. In this case, the indoor air could become very dry if you do not run a humidifier.
Air Conditioner Issues
As air conditioners lower the temperature of the air, they remove humidity. If there is a problem with the air conditioner, it could inadequately remove humidity from the air. This results in higher than normal indoor RH levels.
Typical air conditioner issues that cause high indoor RH levels include an oversized unit, low refrigerant levels, a failing compressor, a faulty blower motor, etc.
Furnace Dries the Air
Gas furnaces heat the air in your home with high heat. This excessive heat evaporates moisture in the air, which lowers the humidity. This works along with the fact that the RH drops simply by increasing the temperature. You can counteract dry air from furnace use by using a humidifier.
Cooking and Hot Showers
What do cooking and hot showers have in common? This might sound like a setup for a joke, but this is no time for dry humor. Both cooking and hot showers create a lot of moisture, which not only affects your kitchen and bathroom, but the rest of your house as well.
Even with proper exhaust ventilation, some moisture created by a hot shower and a boiling pot of water end up circulating throughout your HVAC system. This, of course, increases the humidity in your home, especially if you forget to turn on the kitchen or bathroom exhaust fan.
What Are The Effects of High Humidity Levels?
Persistent high humidity levels in your home can cause poor indoor air quality, leading to detrimental health issues for the occupants. Additionally, high relative humidity can damage the interior of your home and your HVAC system.
A good indication of high indoor air humidity is condensation on the inside of your windows.
Head Colds and Asthma
Moist air could lead to a greater propensity for head colds and asthma flare-ups. Plus, some bacteria and viruses thrive in humid conditions and increase the likelihood of infection.
Most bacteria, viruses, fungi, and other pathogens favor humid air. Coupled with warm temperatures, they easily replicate and have a greater chance of infecting you and other occupants.
Excess moisture in the air or high humidity leads to the growth of mold and mildew. Mold can be difficult to remove from your home once present. Some mold can cause severe respiratory issues.
Rust and Corrosion
When the air in your home is very humid, the extra moisture tends to condense on various surfaces. The water will condense on windows, doors, hinges, floors, vents, and other hardware in your home. Eventually, the moisture will lead to rust, corrosion, and further damage to your home.
It Will Feel Hotter
Humidity levels affect how hot a temperature feels. For example, 70ºF with a relative humidity of 80% feels much hotter than 70ºF with 50% RH. High humidity makes you feel warmer because your body uses evaporative cooling to lower its temperature.
In simple terms, evaporative cooling works like this – your body sweats, and through the evaporation of your sweat, your body cools. This is because it takes thermal energy (heat) to convert the liquid water to vapor.
When it is too humid, the moisture on your skin has nowhere to go. The air is full of moisture already, almost maxing out its saturation, and your sweat cannot evaporate and provide its cooling effects.
What Happens When The Humidity Is Lower Than Recommended?
Similar to high humidity levels, low humidity levels can lead to health issues, discomfort, and problems in your home as well. Here are the common side-effects of a house with low relative humidity.
Allergies and Head Colds
Air with low humidity tends to dry out mucous membranes in your nose, mouth, and throat. The dryness will leave you more susceptible to picking up a bacterial or viral infection.
Most pathogens like bacteria and viruses enjoy moist, damp environments. However, some thrive in dryer conditions and mount a better offense against your immune system if it is compromised due to the dry conditions.
Low humidity leads to a higher cause of static electricity. If you get a shock after walking on the carpet in the winter, this is due to low humidity. With less moisture content in the air, there is less water to conduct your natural charge away from you.
Therefore, your body can carry a higher charge, which will discharge as soon as you touch a grounded object with a significantly lower charge than you.
It Will Feel Colder
Just like how higher relative humidity levels make it feel warmer, the reverse is also true; low humidity levels make the air feel colder than it actually is.
Low humidity levels magnify and heighten the evaporation of the moisture on your skin and the thermal loss it causes (evaporative cooling). This makes you feel chilly even if the indoor temperature is high.
Some Tips For Lowering And Raising Humidity Levels At Home?
No matter what temperature you set your thermostat’s setpoint to, the ideal relative humidity level is between 40% to 60%. However, depending on the weather conditions (the temperature and humidity outside), your indoor relative humidity might be higher or lower than this recommendation.
It might be difficult for your air conditioner to remove enough humidity in the summer, and your furnace could dry the air out too much in the winter.
If your home falls outside of the recommended relative humidity ranges, you can benefit from using a humidifier or dehumidifier, depending on your situation.
A dehumidifier collects excess moisture from the air in your home. The water pools into a reservoir or drain pan that you have to empty routinely, or it automatically drains. You can choose from whole-house dehumidifiers or stand-alone tabletop systems and larger cart-style ones on wheels.
Humidifiers add moisture to the air and increase the relative humidity in your home. In order to provide more moisture to the air, they either need to be connected to a water supply, or you have to refill a tank routinely. Like dehumidifiers, they are available as whole-house systems that connect to the ductwork or as standalone versions which humidify a single room.