Does Furnace Reduce Humidity?

Figuring out whether or not your furnace reduces the humidity level can be quite tricky.

When the furnace heats up the room, it doesn’t change the amount of moisture in the air; however, relative humidity really does change as hot air is able to hold more moisture. The air will also become drier because some furnaces bring dry air from the outside into the house.

Does Heat Affect Humidity?

Relative humidity is a value that represents the percentage of water vapor in the air. This percentage changes when the temperature of the air changes.

For example, as the temperature increases, the air is able to ‘hold’ more water molecules. As a result, the relative humidity decreases.

Does Heating a Room Reduce Humidity?

The total amount of water vapor in the air will not change, if you decide to heat the room. This means that the absolute humidity will stay the same.

However, heating a room does decrease relative humidity as hotter air is able to hold more moisture. As a result, the air will feel drier, even though the overall amount of moisture in it had not changed.

Read: Why Is The Humidity In My House So High After It Rains?

Does the Furnace Lower Humidity?

If your furnace is running, you might feel like the air has become drier. But that doesn’t happen because of the actual heating.

It is because more air from the outside is brought inside the house during the heating process. The outside air is what makes your home feel drier.

Some types of furnaces (like sealed combustion units) draw the combustion air from the outside. This means that such a furnace actually draws the dry air from the outside and lets it out into your house.

This makes the air drier and dry air feels colder, so you end up running the furnace even more often and getting stuck in a vicious circle of low humidity.

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Moreover, a portion of the heated air can escape from your house through cracks and gaps, and that will make the house even colder.

Does furnace reduce humidity? Not quite, as if there wasn’t any air coming from the outside, your humidity level wouldn’t have changed.

Read: Signs Of High Humidity In Your Home

Does a Furnace Increase Humidity?

Some furnaces are called ‘condensing’ units because during their operation they create condensate. So, instead of removing the water vapor, the system actually generates it.

However, that does not affect the humidity in your house.

The condensate generated by the furnaces is drained away by the system. The moisture doesn’t actually come in contact with the air that is sent into the living spaces.

Therefore, the condensation generated by the unit can’t change the humidity in your home.

Bear in mind that there are also furnaces that do not use outside air for the combustion process. They utilize the air from your house.

In such a case, the system won’t be drawing in any dry air from the outside and the humidity level in the house might increase simply because you and your family are creating a lot of moisture (through showers, baths, cooking, watering plants, and so on).

If there is no dry air from the outside entering the house, then the humidity inside will depend on what your family is doing.

Does Oil Heat Dry the Air?

Oil-filled radiators are not that special. They do the same thing as practically any heating source – they don’t increase or decrease the humidity, they simply make the air hotter and that, in its turn, decreases the relative humidity.

The warmer the air the more moisture it is able to hold. So, by not adding any additional moisture, but turning your oil-filled radiator on, you are making the room feel drier.

As the relative humidity drops, our own body moisture is able to evaporate much faster than before. As a result, sweat disappears from our skin in no time, leaving it feeling dry.

The same happens to our nasal passages and mouths, as they will start losing a lot of moisture as well.

But the main point here is that this doesn’t happen because of the oil-filled radiator. It happens because the air got heated.

The great news is that you can add a bit of moisture to the air on your own, so that when the temperature rises, you don’t feel the air drying out:

  • Dry the clothes in the room with the heat source (don’t place the clothes too close to the heater though)
  • Place a whole pot or vase of water next to the heating source
  • Put plants in the room and make sure that they are well-watered
  • Spray the air with water from time to time

Unfortunately, these simple tricks won’t really solve the problem in the long-term. The most important thing that you should do is seal all the cracks and holes in the house and fix the drafty doors and windows.

In such a case, you won’t have any dry air coming into the house through the gaps and you wouldn’t have to use the heater as often as the heat won’t be escaping through the cracks.

Read: Types Of Radiator Heat Systems

Does Propane Heat Cause Humidity?

Propane-burning appliances produce carbon dioxide and water.

If you have a vent-free or an unvented appliance, then the additional moisture won’t get drained anywhere. 

In fact, burning a gallon of propane produces around a gallon of water.

Once the gaseous vapor hits a cool surface, it condensates and turns into liquid water. As windows are, in general, colder than the inside air, this is exactly where the condensation is going to form in the house.

Read: What Is Proper Humidity For Your House And Why?

Will Running Furnace Fan Reduce Humidity?

Yes, you can drastically reduce the humidity in your house, if you turn the furnace fan on. 

The main thing that the fan does is draw more outside air inside. As we have already found out, the outdoor air is, in general, much drier than the air inside the house.

However, this might not be the best option, if you are trying to keep your house warm. The fan will pull inside more cold air and the temperature in the house is going to drop.

Do You Need a Humidifier with a High Efficiency Furnace?

Even though high-efficiency furnaces do create condensation, the moisture stays inside the system and does not affect the humidity level in your house.

Such units are designed to draw air from the outdoors and this is exactly what will make the humidity level drop. So, ideally, you would want to get a high-efficiency furnace together with a humidifier. 

Read: Is It Worth Getting A High Efficiency Furnace? And Why?

When Should I Turn on My Furnace Humidifier?

You can choose to always use the humidifier together with the furnace or turn it on only when you start to notice that the air in the house is dry.

In any case, you should be monitoring the humidity level in your house to ensure that it’s between 30% and 40%. If you have a humidistat, it is absolutely safe to run the humidifier all the time.

How Do I Adjust the Humidity in My Furnace?

Whole-house humidifiers generally come with a humidistat. Locate the control panel for the humidifier and adjust the humidity setting. An analog humidistat will have an adjustment dial, while a digital device usually has up and down arrows that you can use to adjust the humidity level.