Do Oil Filled Heaters Dry The Air? (Explained Simply)

Many people will tell you that oil filled heaters dry the air in a room. That is their honest perception through uncomfortable experiences of dry mouths and itchy skin.

But it’s not true that their oil filled heater is drying out the air. There’s a scientific explanation to this that’s based on some complicated terminology.

But this article explains what’s going on in plain English to make it easy to enjoy a warm comfortable room.

Do Oil Filled Heaters Dry The Air?

Let’s walk through what happens when your oil filled radiator heats the room.

The air gets warmer, of course. But the first important point is that warmer air can hold more moisture than colder air. The higher the air temperature, the higher it’s capacity for holding moisture.

The next important point is that an oil filled heater doesn’t add moisture to the air.

Some heat sources produce moisture. Gas heaters are the most common examples. But oil filed heaters do not.

I’m assuming that you’re not drying wet clothes beside the radiator! I’ll cover that later. But for now, we’ll take the case where you’ve done nothing but turn on the oil filled radiator in a cold room.

So, our radiator has warmed the air. And warm air can hold more moisture. But we haven’t added any moisture.


Relative Humidity

Now for a little science in the form of relative humidity. The relative humidity of this room is the amount of moisture divided by how much moisture the air could hold at its current temperature.

Simple maths: RH = Moisture / Capacity

Our oil filled radiator has heated the air, and therefore increased the bottom part of this division: the capacity. The top part, the moisture, has stayed the same.

So, the relative humidity drops as the room is heated.

By the way, this is true for any heat source that doesn’t add moisture. Oil filled radiators aren’t that special!

You’re probably still wondering what this has to do with the room feeling dry.

The reason is that relative humidity determines how we experience dryness in the room.

Dryness And Relative Humidity

When the relative humidity drops, our own body moisture evaporates more easily. So, our sweat evaporates faster which makes our skin feeling drier. This may get to the point of uncomfortable itchiness.  

Our mouths and nasal passages will also lose more moisture. This can get to the point where a dry mouth can be uncomfortable. At worst, dry sinuses can give us headaches.

But this dry discomfort isn’t due to your oil filled radiator heating the room. Any heat source without moisture will cause the same effect of decreasing relative humidity.

The solution isn’t to rip out your radiators! If you have uncomfortably dry rooms, you can increase the moisture levels while ensuring there is proper ventilation. Of course, high humidity can be even more uncomfortable.

How To Reduce Dryness In A Room

You may have come to this article wondering if your feeling of discomfort is due to your oil filled heater. And we’ve said that they are simply heating the room, so are not at fault. But that doesn’t solve your problem!

So, I’ll give a few tips here.

Your oil filled radiators won’t add moisture to the room, but you can add another appliance that will! In other words, a humidifier adds moisture to warm dry air.

But before you rush out to buy more equipment, here are some quick solutions to try.

  • Add household plants to the room and keep them well-watered
  • Dry your clothes in the room
  • Put a wet sponge into a bowl in the corner of the room
  • Place a pot of water on the radiator (this won’t be possible for all radiators)
  • Place a pan of water near a window so that it catches sunlight
  • Dampen your curtains with a light spray of water (watch out for mildew)
  • Use a spray bottle periodically to spray the air

Unfortunately, these simple remedies aren’t going to work in many situations. Does your room get so cold that you constantly have to crank up the heat? You may simply have one or more draughty leaks that need sealing.

Sealing leaks and draughts

When you heat the room, the moisture tries to flow to areas with a colder temperature. This is most likely outside the house.

Remember our simple equation that Relative Humidity = Moisture / Capacity?

If you reduce the top part of this equation, you will lower the relative humidity.

So, the more moisture that can escape from the room, the drier it will feel. Of course, you want healthy ventilation. But you don’t want draughty leaks letting too much moist air rush out.

A More Technical Explanation Of Relative Humidity

The only technical term I threw into the plain-English explanation was Relative Humidity. I skipped around a few other terms. If you’re interested in getting into the weeds, this section is for you.

The absolute humidity is the amount of moisture in the air, while the relative humidity is this quantity divided by the capacity of the air to hold moisture.


The rate of evaporation measures how fast the moisture vaporizes, which of course is dependent on the room temperature.

The rate of condensation measures the reverse of evaporation. Think of water appearing on your windowpane. This rate depends on other factors such as air pressure.

Relative humidity is the rate of condensation divided by the rate of evaporation…times one hundred.

RH = condensation rate / evaporation rate * 100

Penn State University – Introductory Meteorology

Low relative humidity means that the evaporation rate is considerably higher than the condensation rate.

More Questions?

Check out our article on whether you can leave your oil filled heater on all the time.

Dean Casey
About Dean Casey

Hi, I'm Dean Casey, the founder and chief editor of

With over 15 years of experience in the HVAC industry, my passion is helping homeowners achieve optimal comfort and energy efficiency in their living spaces. As a certified HVAC technician and consultant, I have developed a deep understanding of home heating systems, insulation, and energy-saving practices.

I started this blog to provide well-researched, practical advice to homeowners looking to improve their home's heating performance and reduce energy bills. Whether it's comprehensive guides, hands-on product reviews, or expert tips, my goal is to share valuable information with you, my readers.

I enjoy spending time with my family and exploring the great outdoors when I'm not busy writing and researching. I'm also an avid DIYer, always eager to tackle new home improvement projects and share my experiences with you.

If you have any questions or comments about home heating, please don't hesitate to reach out through the contact page on the website. I'm always happy to help!

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