Are Ventless Gas Heaters Safe?

Ventless gas heaters form a more effective heating source for indoor and semi-outdoor environments. They are more effective than vented gas heaters because they dissipate all the heat back into the room.

Vented heaters lose a small amount of heat through the venting. However, there are many concerns about the safety of ventless heaters. This article will attempt to answer whether ventless gas heaters are safe.

We will walk you through some of the risks of using ventless gas heaters and how you can minimize them. We also give you valuable tips on using ventless natural gas heaters as supplemental heat sources indoors.

Are Ventless Natural Gas Heaters Safe?

The short answer to this question is that ventless heaters are not safe because they exhaust all the combustion products back into the room. Thus, ventless heaters release the carbon monoxide, carbon dioxide, nitrogen dioxide, and even water vapor back into the room where they are installed.

However, they are more effective than vented natural gas heaters because they do not lose even a fraction of the heat through vents. 

Are Ventless Propane Heaters Safe? 

Ventless propane heaters are not safe because they dissipate all the combustion products into the room. The combustion of propane produces several products, including carbon dioxide, carbon monoxide, water vapor, and nitrogen dioxide.

Carbon monoxide and nitrogen dioxide are highly toxic gases. If your ventless propane heater releases them in high quantities over time, it will pose a danger for humans and animals in the house. 

How do Ventless Gas Heaters Work? 

Ventless gas heaters produce heat energy by burning gas and oxygen. They are portable heating devices that are not vented to the outside. Venting is vital for heating devices because it helps provide an escape route for all the combustion products.

Burning any fossil fuel produces the following: carbon monoxide, carbon dioxide, water vapor, and nitrogen dioxide. In addition, the combustion process may produce soot and smoke. Soot and smoke may be significant if the burning process is not clean or complete.

Ventless gas heaters are designed to burn the air and gas fuel mixture completely. Thus, ideally, ventless gas heaters are not expected to produce significant amounts of these byproducts.

However, in reality, ventless gas heaters end up producing these byproducts. This is why several independent organizations recommend emission levels for ventless gas heaters and related devices. 

Unlike vented gas heaters, ventless gas heaters draw oxygen from the room. Unfortunately, they also directly discharge all the heat and byproducts of the burning process back to the room.

Thus, although ventless gas heaters are an effective way of heating a house, they do pose several dangers when they operate. Let us delve into some of the dangers of operating ventless natural gas heaters. 

Are Ventless Gas Heaters Safe? 

Many people have concerns about the safety of ventless gas heaters. Indeed, these concerns are valid, given how ventless gas heaters function. So let us delve deep into the subject of whether ventless gas heaters are safe. 

Dangers of Ventless Gas Heaters

The dangers of a ventless gas heater arise from the effect of the products of the combustion process, which it deposits into the house. Each byproduct poses a unique danger to people, pets, and even some objects in your home. 

  • Carbon monoxide: Carbon monoxide is a highly toxic gas produced because of the incomplete combustion of fossil fuels. Incomplete combustion of fossil fuels occurs when there is a smaller than expected amount of oxygen in the air-fuel mixture. When humans and animals inhale relatively small amounts of carbon monoxide, they begin to experience mild symptoms of carbon monoxide poisoning. The symptoms usually include dizziness and nausea. Thus, carbon monoxide poisoning is one of the biggest dangers of using ventless natural gas heaters. 
  • Water vapor: Water vapor is a natural product of combustion. Although you may not realize it at once, using a ventless heater leads to an abnormally high deposition of water vapor into your home. If there is enough ventilation, this may not be a problem. The water vapor eventually finds its way out of your house through the natural ventilation process. However, if the house is poorly ventilated, the water vapor may trigger mold growth after some time. 
  • Carbon dioxide: Carbon dioxide is a relatively non-toxic gas when compared to carbon monoxide. However, you will not enjoy your indoor environment if large amounts of carbon dioxide are inside your house. In addition, the gas has a pungent smell that interferes with the indoor air quality. Ventless natural gas heaters dissipate all the carbon dioxide they produce back into the home. Although there are recommendations nowadays on the maximum amounts that a heater should discharge for it to be used safely, you should still be aware of the danger of using a ventless heater in your home. 
  • Nitrogen dioxide: Nitrogen dioxide is a toxic gas. Although the amounts of gas that your ventless natural gas heater deposits into your house are negligible, things may change pretty fast if a technical fault occurs. If your heater deposits vast amounts of this gas, you may begin to experience its toxic effects. 

Ventless Gas Heater Safety Tips

Not all is lost for ventless gas heaters. You can comfortably use them to provide warmth in your home. Here are some essential tips to help you use ventless natural gas heaters safely. 

  • Stick to the operational and maintenance recommendations as indicated in the manual by your ventless gas heater manufacturer. Doing this will help prevent technical faults and subsequent accidents when your ventless natural gas heater runs. 
  • Install carbon monoxide alarms: Carbon monoxide alarms warn one when there is a dangerous amount of highly poisonous gas in the indoor environment. These alarms help to prevent the occurrence of carbon monoxide poisoning. 
  • Clean the burner of your heater regularly: Regular cleaning of the heater’s burner removes soot and other contaminants that usually stick in the burner. In addition, this practice minimizes the number of contaminants released into your house while the ventless natural gas burner is running. 
  • Ensure there is enough ventilation in the house: It is a big mistake to place your ventless natural gas burner in confined spaces with very little ventilation. Your ventless gas requires a large amount of air for it to burn the natural gas altogether. 
  • Do not leave your ventless gas heater unattended: Always switch off your ventless gas heater when you leave home, even for a few minutes. 
  • Do not place objects on the top of your heater: The surface of the heater may become hot enough to cause fires if you place highly combustible materials at the top. Similarly, ensure that you keep combustible materials well out of the way of your ventless natural gas heater. All space heaters can cause fires if they are close to combustible materials. 
  • Use an appropriately sized ventless gas heater: Using either a small or a large heater poses safety risks. A large heater will produce excess heat and many combustion products. A small heater will not produce the amount of heat necessary for warming the air in the entire room.

Frequently Asked Questions About Gas Heater

Do all gas heaters need to be vented?

All gas heaters don’t need to be vented; however, venting your gas heater is always a good idea. Venting your gas heater will help you avoid the problems and dangers of using a ventless gas heater. Even if you use a ventless gas heater, you will have to keep the room properly ventilated.

Nevertheless, venting a gas heater is a complicated and time-consuming process. You will have to let a certified HVAC professional vent your gas heater. 

Is it safe to use a gas heater indoors?

Although there are specific brands of gas heaters marked as safe for use indoors, they may not guarantee your safety while you do so. This is because gas heaters produce small amounts of poisonous gases and other contaminants. The contaminants may interfere with the overall quality of indoor air in your house.

Therefore, if you use them indoors, you should be aware of how you will ensure that these contaminants do not accumulate in your home. 

Can I use a ventless heater in my garage?

Yes, you can use a ventless heater in your garage if you take precautions. However, using a ventless heater in your garage exposes you to multiple dangers. The most common and serious danger is carbon monoxide poisoning. This problem can develop if there is not adequate ventilation in your garage.

However, if you have enough ventilation in your garage, you can safely use a ventless heater to provide warmth. Ensure enough openings to let in the fresh air and move out the stale air that builds up as the ventless heater releases gases and particulates.

Can I use a ventless heater in the basement?

You can use a ventless heater in your basement; however, you need to be cautious about the ventilation in your basement. If there is no adequate ventilation in your basement, it may not be a good idea to use a ventless heater in the basement.

Basements hardly have enough ventilation to support the operation of a ventless gas heater. The heater needs a steady supply of air for it to function normally. The fresh air usually compensates for the loss of oxygen that the heater takes from the air to support the combustion process.

In addition, the flow of fresh air makes it possible for the contaminants that the heater produces to be neutralized. Therefore, using your heater in your basement may not be a good idea unless you are sure about the ventilation.  

Why does my ventless gas heater smell?

Your ventless gas heater smells because it produces several gases with different smells. Carbon monoxide is odorless, but carbon dioxide has a characteristic pungent smell. In addition, nitrogen dioxide has a foul smell.

These two gases accumulate in the atmosphere after your ventless gas heater operates for a while. They are responsible for the smell of your heater. You can deal with the smell by limiting the time you run your ventless heater.

Avoid leaving the ventless heater on for a long time. You may also ensure a good air supply into the room where the ventless gas heater is placed. The inflow and outflow of the air will help to minimize the smell from your ventless gas heater.  

Do ventless heaters create moisture?

Ventless heaters create moisture. The moisture comes from the combustion of the fuel. The combustion process produces a mixture of gases, heat, and water vapor. If the ventilation of your house is poor, the water vapor may accumulate on surfaces over time.

This may cause rots and molds on wooden surfaces after some time. However, if there is enough ventilation in your house, the moisture from your ventless gas heater will not cause many problems. This is because the excess moisture will eventually be carried outside by the outflow current. 

Do ventless heaters produce carbon monoxide?

Generally, ventless heaters produce negligible carbon monoxide when running ideally. This is because they are designed to burn all the natural gas and oxygen they take in from the atmosphere. However, if this clean combustion process does not occur, your ventless gas heater will produce carbon monoxide.

This is why it is wise to install carbon monoxide alarms if you intend to use your ventless gas heater indoors. The alarms help prevent carbon monoxide poisoning by alerting you when there is carbon monoxide gas in the atmosphere. 


Generally, ventless natural gas heaters are not safe. Any heating device that burns fossil fuels to produce heat energy operates safely when vented. Venting helps to provide a safe passage for all the toxic and non-toxic byproducts of the combustion process that these heaters produce.

However, if not properly vented, your ventless natural gas heater may pose a danger to everyone in the house. Apart from the risk of carbon monoxide, poisoning, using ventless natural gas poses the danger of interfering with the indoor air quality of your home.