It seems that you can never be too careful when it comes to clothes dryers with all the warnings that are posted on every corner of the internet. The two major concerns that come to mind are carbon monoxide and lint. The former being slightly more ominous since it is much more difficult to detect.
Ventilation regulations in the International Residential Code (IRC) apply to all dryers, not just gas ones. This is a good indication that, even though combustion gases are not a feature with electric dryers, it is still necessary to safely vent them.
Electric dryers do not produce carbon monoxide. These appliances use electricity to create their heat in coils through resistance rather than a gas fuel that requires combustion. However, unless the machine is a ventless model, it must still have a vent to remove the by-products of operation.
Carbon Monoxide Is a Combustion By-Product
When oxygen is combined with the gas fuel used for dryers, it rapidly reacts and produces carbon dioxide during complete combustion. Complete combustion takes place when there is sufficient oxygen present for the combustion process.
Gas dryers are provided with combustion air to ensure that complete combustion occurs. So, if a gas dryer is installed and operating correctly, then carbon monoxide should not be an issue.
When there is an insufficient oxygen supply for combustion, the process can still occur, but the result is carbon monoxide instead of carbon dioxide.
The conditions for incomplete combustion arise when there is incorrect combustion air provision or when exhaust systems present in the room remove air faster than it can be replaced (requires makeup air).
The amount of carbon monoxide that can be produced is relatively small, but it is still unsafe to allow it to build in your home every time you use the dryer as it poses a health risk.
In addition, carbon monoxide becomes more of an issue when the gas dryer is vented incorrectly.
Combustion gases travel through the appliance with the heated air. They pass into and through the drum to the vent on the other side, and from there, the exhaust is blown out of the dryer.
Therefore, it is essential to vent a gas dryer correctly through its own exhaust system that terminates outdoors.
Electric Dryers Don’t Use Heat From Combustion
Now, you probably noticed that we just spoke a whole lot about gas dryers, while your question is about electric dryers.
The reason for this is that, while gas dryers require electricity on top of the gas fuel, electric dryers exclusively use electricity and an electric heating element to produce heat for the appliance’s operation.
So, electric dryers do not use a gas fuel. This means that they produce hot, humid, lint-carrying air, but they do not produce combustion by-products, like carbon monoxide.
It also means that while gas dryers can use a regular 110/120V outlet, their electric counterparts need a specialized 220/240V outlet (unless they are compact models).
Electricity is channeled through the coil (element) that resists this flow, allowing electrons to gather here, which results in heat energy. The blower pulls air from around the dryer into the machine, where it passes by the coils.
Heat transfers to the air from the coils and is then directed through the drum, where it evaporates water from the clothing and out through the internal dryer vent to the exhaust system.
How to Tell if Dryer Is Gas or Electric (Without Moving the Dryer)
Still Not Safe to Vent Electric Dryers Indoors
So, if there is no risk of carbon monoxide, is it really necessary to vent an electric dryer?
It is still not considered safe to vent an electric dryer indoors. There are multiple concerns and issues you will encounter if the dryer is not vented, including the damage to your home from the heat and moisture and the danger of lint.
Dryers are either designed to be vented or not. It is possible to purchase a vented electric dryer or a ventless electric dryer, which deliberately provides alternative methods of handling moisture and lint.
However, if the manufacturer requires the electric dryer to be vented outside, doing otherwise is considered non-compliant according to building code regulations.
Sources
https://www.thespruce.com/how-does-a-clothes-dryer-work-2145846