Dangers Of Ventless Propane Heaters


Ventless heaters, also popular as unvented or vent-free heaters, are considered some of the most efficient gas heaters. Some are up to 99.9% efficient.

The high efficiency means that they waste very little fuel. Only 0.1% or less of the gas goes to waste – a significant advantage over vented units that are mostly around 90% efficient. It’s often the main attraction among consumers who choose vent-free gas heating over vented options.

Ventless gas heaters are also easier and cheaper to install. Since you don’t need to budget for the venting system, the installation process is smooth. They’re also generally less expensive compared to their vented counterparts.

Unfortunately, vent-free gas heaters are also inherently riskier compared to vented models. Since they vent all byproducts inside the room, any poisonous materials in the byproducts can pose a risk to you and your family.

If you’re considering purchasing one, you may want to learn about the potential risks so you can make an informed decision.

How Ventless Propane Heaters Work

Let’s begin with a recap of how ventless gas heaters work to determine the potential byproducts and why you should be concerned.

As the name suggests, ventless gas heaters are gas heaters that don’t vent air outside the house. Two things usually define the heaters;

  • They draw the oxygen needed for combustion from the room: This is different from vented systems with vents that bring combustion oxygen.
  • They vent all combustion byproducts inside the room: This is also different from vented systems that have vent pipes that ferry combustion byproducts outside the house.

The heaters produce very few combustion byproducts, with water vapor and carbon dioxide often making over 99% of the byproducts.

What are the Potential Dangers?

Unfortunately, even the most efficient ventless propane heaters produce a few toxic byproducts that may be harmful to your health and the health of your loved ones.

Some of the byproducts can also cause damage to your home. The most common risks are as follows;

1. High CO2 levels can be risky

Although carbon dioxide is the fourth most abundant gas on the earth’s surface, prolonged exposure to high gas levels can be harmful to your health.

First off, a high concentration of carbon dioxide in the air can displace oxygen. This is a significant problem considering that, as we’ve seen, ventless gas heaters depend on indoor oxygen for combustion. If the combustion process depletes oxygen in the room and then you have carbon dioxide displacing the little oxygen left in the home, you’re in trouble.

Common symptoms of overexposure include depression of the central nervous system, eventually resulting in rapid breathing, rapid heart rate, clumsiness, emotional upsets, and fatigue. As the oxygen levels deplete further, nausea and vomiting may follow. Beyond that, collapse, convulsions, and death are possible.

2. Excess water vapor is also bad for your health

Water vapor is harmless in small quantities. However, ventless heaters produce a lot of water vapor. Studies show that a 20,000 BTU ventless propane heater produces about ¼ gallon of water vapor per hour when running.

Overexposure to water vapor increases a person’s susceptibility to upper respiratory disorders. The reason is that mold and fungi that trigger respiratory symptoms thrive in conditions with 60% humidity. Dust mites, bacteria, and viruses also enjoy conditions with 60% humidity or higher.

Worse still, even typically risk-free items such as carpets tend to emit toxic chemicals in excessively damp conditions in a process known as off-gassing. Off-gassing is caused by increased concentration of noxious chemicals when there’s overexposure to water vapor. It can make people experience skin, eye, and throat irritation.

3. Risk of carbon monoxide poisoning

Carbon monoxide is typically produced when there’s incomplete burning. In most cases, it happens when there’s not enough oxygen for the combustion process. Therefore, instead of producing CO2 and water, the combustion process produces traces of carbon monoxide.

The good news is that the high-efficiency levels of vent-free heaters often mean that the likelihood of carbon monoxide is very low. However, “low” doesn’t mean it can never happen – and CO, even in small quantities, can be very dangerous.

According to OSHA, carbon monoxide, when breathed, displaces oxygen in the blood and deprives the heart, brain, and other vital organs of oxygen. It means that overexposure to carbon dioxide at high concentrations can overcome you in minutes – causing suffocation and loss of consciousness.

Even in small doses, CO inhalation causes a tight chest, fatigue, dizziness, drowsiness, and nausea. After some time, you may also experience vomiting, confusion, and muscle weakness. Even death is possible.

4. Nitrogen dioxide poisoning

Another ever-present byproduct of ventless gas heating is nitrogen dioxide. It’s a reddish-brown gas that has a sharp, harsh odor at high concentrations.

However, at low concentrations, the color and scent aren’t apparent. This is usually the case in ventless gas heating. The extremely low levels of NO2 often mean that the gas is colorless and odorless.

Unfortunately, nitrogen dioxide, even at low concentrations, can be dangerous. The gas is known to irritate the mucous membrane, potentially triggering or worsening respiratory issues such as lung disease, asthma, and obstructive pulmonary disease. Bronchitis, pneumonitis, and dyspnea are also potential risks.

Remember that nitrogen dioxide also forms nitric acid when it comes in contact with water. This means that it’s even more toxic than nitric acid, though nitric acid may kill faster at lethal concentrations. The acid can scar bronchioles in the lungs resulting in a life-threatening episode.

The level of damage depends on the concentration levels of the inhaled NO2 and the duration of exposure. 

5. Potential damage to the property

Finally, vent-free gas heating isn’t just bad for your health. It can also cause significant damage to the property and your items.

  • Water damage: First off, we’ve seen that vent-free heating results in a lot of moisture. Moisture can damage your books and other paper-based items such as documents and cartons. It doesn’t end there. Moisture can also condense to form water that can pool on the floor, causing further damage.
  • Mold formation: When the moisture condenses on the walls, it can form a breeding ground for mold and mildew. Mold and mildew are known to trigger allergies and cause other respiratory issues. Mold can also weaken wooden structures.
  • Wall damage: Both mold and water can damage your walls. Whether you use wallpaper or paint, the damp conditions can make it come off, while mold can destroy it. Moisture can also seep into the wall and weaken it.
  • Potential smoke damage: Most vent-less heaters are so efficient that they don’t produce smoke. However, as oxygen levels deplete, you may notice traces of smoke. Smoke can affect your health and is just as bad for your home as it blackens everything, from the walls to your items.

Be Warned

The dangers listed above don’t mean that safe ventless gas heating is impossible. Even vented gas heating systems are dangerous to a degree. It would be best if you were more careful.

Experts recommend that you begin by acquiring an Oxygen Depletion Sensor (ODS) to track oxygen levels in the home. This way, you can shut off and fix the heater whenever needed to prevent poisoning and relevant damages.

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