Vent Free Gas Heaters 101: How Safe are Ventless Gas Heaters

Are you considering using a vent-free natural gas heater to heat your home this winter? If so, you may be wondering if these heaters are safe to use. After all, natural gas is a highly flammable fuel, and you want to make sure that you and your family are protected from any potential hazards.

In this blog post, we’ll explore the safety of vent-free natural gas heaters and provide you with all the information you need to make an informed decision about whether or not to use one in your home. So if you want to stay warm and safe this winter, read on!

What Are Ventless Gas Heaters?

Ventless gas heaters, also known as vent-free gas heaters, are heating appliances that use natural gas or propane as a fuel source and do not require a chimney or flue for venting.

They operate by burning the fuel to produce heat, which is then distributed throughout the room or space using a fan or blower.

Ventless gas heaters are typically small and portable, making them a convenient and easy-to-use option for supplemental or spot heating in a home. They can be installed on a wall, on a tabletop, or on the floor, and are often used as an alternative to traditional heating systems, particularly in homes without access to a central heating system.

There are two main types of ventless gas heaters: infrared and blue flame. Infrared ventless gas heaters use infrared technology to directly heat objects and surfaces in a room, while blue flame ventless gas heaters use a burners to produce heat, which is then circulated throughout the room using a fan or blower.

Ventless gas heaters are generally considered to be a more efficient and cost-effective heating option than traditional heating systems, as they do not require the installation of ductwork or venting and do not suffer from heat loss through the chimney or flue. However, they do have some potential safety concerns, which we will discuss in more detail below.

Dangers of Ventless Propane Heaters

One of the main questions people have about ventless gas heaters is whether or not they are safe to use. The short answer is that ventless gas heaters can be safe to use if they are properly installed and used according to the manufacturer’s instructions.

However, there are some potential safety concerns that you should be aware of before deciding to use a ventless gas heater in your home.

1. Carbon Monoxide Poisoning

Carbon monoxide (CO) is an odorless, colorless gas that is produced when fuels such as natural gas, propane, and wood are burned. It can be harmful or even deadly if inhaled in large amounts.

If a ventless gas heater is not working properly, it can release CO into the air. Here are some safety steps you can take to avoid the danger of carbon monoxide poisoning when using a ventless gas heater:

  1. Make sure the heater is properly installed and maintained: Ventless gas heaters should be installed and serviced by a licensed professional. If you have a ventless gas heater, make sure it has been installed and maintained according to the manufacturer’s instructions and local building codes.
  2. Follow the manufacturer’s instructions for use: Each ventless gas heater is different, so it is important to follow the manufacturer’s instructions for proper use. This includes information on proper ventilation, fuel type, and operating temperature.
  3. Keep the heater clean and well-maintained: Make sure to clean the heater and its venting system regularly, and have it checked by a professional if you notice any issues.
  4. Use the heater in a well-ventilated area: Ventless gas heaters should not be used in small, enclosed spaces without proper ventilation. Make sure there are windows or doors that can be opened to allow fresh air to circulate.
  5. Install a carbon monoxide detector: Carbon monoxide detectors can alert you to the presence of dangerous levels of CO in your home. Make sure you have one installed near the heater and in other areas of your home as well.

3. Risk of Fire

Like any other appliance that uses natural gas or propane as a fuel source, ventless gas heaters have the potential to ignite and cause a fire if they are not not properly maintained or if flammable materials are placed too close to the heater.

Vent-free heaters produce a small flame that can ignite nearby materials if they come into contact with the flame or if the flame is not properly contained within the heater.

3. Mold Growth

Vent-free gas heaters can produce high levels of moisture and humidity in the room, which can create the ideal conditions for mold growth. Mold is a type of fungus that thrives in damp, humid environments and can grow on a variety of surfaces, including walls, ceilings, and other building materials.

Mold can be harmful to humans and pets, as it can release spores into the air that can be inhaled and cause respiratory problems, allergies, and other health issues. Mold can also weaken and damage the structure of a building, leading to costly repairs.

Ensure that the room is well-ventilated and the heater is placed in a location where the exhaust gases can disperse easily. If you notice any signs of mold growth, such as a musty smell or visible growth on walls or other surfaces, it is important to address the problem as soon as possible to prevent it from spreading and causing further damage.

If you have any concerns about the safety of your vent-free heater, it is best to consult a professional heating and cooling technician.

Are Ventless Heaters Safe?

A ventless heater will be just as safe as a regular one if you maintain it properly and follow the manufacturer instructions.

Additionally, the ventless heaters that are used in homes today are much more fuel and air efficient than the earlier models which fueled fireplaces, creating a safe, clean and energy-efficient heating solution.

The low emission ventless heater is marketed for home use. One of the main benefits is that it doesn’t need an exhaust stack or chimney because it emits less pollutants to the atmosphere. It’s also made from materials not typically associated with fire hazards so you don’t have to worry about burning your house down with faulty wiring.

Ventless gas heaters are safe to use, but they can be dangerous if you don’t follow some simple safety tips. Ventless gas heaters should not be used in the following areas: enclosed spaces like a home or garage, near combustible materials such as furniture and curtains, and anywhere where oxygen is limited.

More than ten million American homes now have vent-free supplementary gas heating products. why do more and more home buyers demand these highly efficient, clean-burning, and safe appliances?

It’s because home buyers learn from their trusted neighbors, relatives, co-workers, and friends what works – and what doesn’t work – for them. They find out from appliance users themselves that vent-free gas products deliver clean heat that is safe to use and remarkably efficient.

So when Americans shop for new homes, vent-free gas appliances are often high on their “wish list.” And that’s why vent-free products mean profitability for the home builder and remodeler. Installation costs are up to 60% lower than the cost of installing vented heating appliances.

Vent-free means there’s no need to install a vent to the outside, no chimney, no hole-in-the-roof. All you need is access to a gas line, so you can place a vent-free gas appliance just about anywhere.

are ventless gas heaters safe

This guide is designed to help home builders and remodelers to make informed decisions when specifying supplementary heating equipment by providing the facts you need:

  • FACT: Vent-free products offer substantial savings on installation costs.
  • FACT: Home buyers value vent-free appliances for their beauty and their ability to significantly reduce heating bills.
  • FACT: Vent-free products are proven to be the safest supplemental heating product in use today.
  • FACT: Vent-free appliances meet or exceed nationally-recognized Indoor Air Quality guidelines.

Annually, more than 1 million supplementary gas vent-free heating appliances are sold today. It’s a grassroots revolution in home heating comfort. Homeowners delight in bringing their friends and neighbors in on their discovery: that ventfree supplementary heating is a technology whose time has come. So just ask the comfy-warm owners of vent-free gas appliances what kind of supplementary heating they’d like in their next home. You’ll hear “I love my VENT- FREEDOM!” ten million times.

See: Pros and Cons of a Vent-Free Gas Fireplace



are ventless heaters safe

But perhaps even more important than the entrancing beauty of vent- free appliances is their practicality. Today’s home buyers want heating security. They want safe, clean, efficient heat that is always there when they need it.

  • Economical to Install. There’s no need for a vent to the outside – no chimney, no hole-in-the-wall. The installation goes faster, costs much less, and the vent-free appliance can be placed just about anywhere in the home – in a corner, under a window, even as a room divider.
  • Increased Value for Home Buyers. Give home buyers the alluring fireplace or heating stove they dream about. Vent-free gas products operate on either natural gas or propane and are available in a huge variety of sizes and styles to suit any decor.
  • Safe Supplementary Heating. All vent-free gas appliances are equipped with an Oxygen Detection Safety-Pilot, which automatically turns off the gas supply if the oxygen level in the room approaches an unsafe level. With installations in more than ten million American homes since 1980 – and more than 50 million worldwide – vent-free products have compiled an excellent safety record.
  • Safe Indoor Air Quality. Extensive independent testing has verified that vent-free gas appliances meet or exceed the nationally recognized guidelines for indoor air quality, even for sensitive populations, such as children, pregnant women, and the elderly. Vent-free products are tested by independent appliance testing laboratories to ensure they comply with ANSI Z21.11.2, a standard established under the auspices of the American National Standards Institute. This standard is maintained by a committee whose members include utilities, manufacturers, government agencies, code officials, and consultants. The Committee has removed from the standard all language concerning sensitive populations because of vent-free products’ excellent health and safety record over the past twenty years.
  • Wide Range of Sizing. Vent-free appliances are available in sizes ranging from 2,000 to 40,000 Btu. These appliances can be controlled by the homeowner to deliver just the right level of heating comfort.
  • Meet Recommended Humidification Requirements. An independent research study has verified that vent-free gas products provide a small portion of desirable indoor humidity, exceeding Association of Home Appliance Manufacturers recommendations only in small, tightly-constructed homes where the product is oversized for space and operated at output levels that exceed human comfort.
  • Emergency Heating. Most vent-free gas products do not use electricity, so homeowners value them highly for emergency heating in times of power outages.

“For many homeowners, vent-free gas products are the right answer: they’re economical to install, and they’re safe to operate. You can count on it, if any of my clients have a safety problem, they’ll call me right away. But I’ve never had a safety problem with vent-free gas products.”



Although millions of American homeowners commonly use vent-free gas appliances, there is still some confusion in the marketplace about these products. Even worse, much of this confusion is based on the dissemination of inaccuracies and misconceptions about vent-free products.

Some hard facts are in order. On these pages, we address several assertions that have been made about vent-free gas appliances.

Assertion: Some people have complained of health problems

Fact: While some people may have special sensitivity to various household environmental factors, there are no independent, documented studies that show vent-free products cause illness or negative health effects.

On the other hand, a thorough, well-documented independent study has been conducted on the effects of vent-free gas product emissions. The study concluded that vent-free gas heating products performed well within all nationally recognized guidelines for indoor air quality.

Assertion: There are concerns about Carbon Monoxide (CO) emissions from vent-free appliances, especially in households with children, pregnant women, and elderly people.

Fact: The effects of vent-free products’ emissions on sensitive populations were tested in the extensive independent study. This research used as its criteria the recommended maximum levels of CO as set by the Consumer Product Safety Commission (CPSC), with sensitive populations – such as children, pregnant women and the elderly – as the benchmark.

The results of the research proved that vent-free gas heating products performed well within the CPSC guidelines for Carbon Monoxide and all other indoor air quality guidelines by OSHA, NIOSH and ASHRAE.

Assertion: There is no standard that regulates the safety of vent-free products.

Fact: Vent-free products conform to the national product safety standard, ANSI Z21.11.2. This standard strictly compels vent-free products to satisfy many construction and performance requirements that, among others, include tests for proper combustion under abnormal conditions.

All vent-free gas products sold in the U.S. are certified by recognized listing agencies for compliance with this ANSI standard to assure their safety and performance.

Assertion: There is nothing to prevent a thrifty homeowner from using a vent-free gas heater as a sole heat source.

Fact: Surprisingly, there are homeowners who improperly use even their cooking ranges as a sole heat source. The fact is, consumers must be informed on how to use any new gas appliance in the home.

All major building codes categorize vent-free products for supplemental use and require that a primary source of heat (e.g., a furnace) be present in the home before a vent-free product can be installed. It is clearly stated in the operating instructions of every vent-free appliance that vent-free gas products are only to be used for supplemental heating.

Assertion: There are many places where vent-free gas products are not accepted for use.

Fact: Currently, the vast majority of states in the U.S. allow for the sale and installation of vent-free supplemental gas heat appliances. Massachusetts is now in the regulatory stage following the change in the law.

The International Mechanical Code (IMC), the National Fuel Gas Code, and most other codes in the U.S. allow for vent-free appliances. Unfortunately, the Uniform Mechanical Code (UMC) does not permit the use of vent-free products; however, many localities are now adopting the IMC over the UMC, and therefore, allowing the use of vent-free products.

Assertion: Vent-free products produce too much heat in tightly constructed homes.

Fact: The heat output of vent-free products that are properly sized can be easily controlled by the homeowner and set to the desired comfort level.

However, installers of vent-free appliances in homes that have extremely tight construction should be sure to follow the manufacturer’s instructions and building code requirements for supplying ventilation and combustion air.

In some cases, additional mechanical ventilation may need to be added before installing a vent-free gas heating appliance.

Assertion: If a customer buys a vent-free gas appliance, it is necessary to purchase a quality Carbon Monoxide detector as well.

Fact: All homes, whether their energy source is electric, gas, wood, or oil, should have a listed Carbon Monoxide (CO) detector. Primary sources of CO concern are automobiles, indoor grilling on hibachis, and gas appliances that have not been properly maintained.

The independent research study on vent-free products concluded after extensive testing that CO emissions from vent-free gas products are well within nationally recognized indoor air quality guidelines, even for sensitive populations.

Assertion: Ceiling fans should not be installed in rooms with vent-free fireplaces.

Fact: Ceiling fans may be used to help distribute the heat, however, fans should not be allowed to blow directly into the fireplace to avoid any drafts that alter burner flame patterns, which can result in sooting. Assertion: All vent-free appliances have inputs of as much as 40,000 Btu of heat, but most rooms need only 5,000 to 15,000.

Fact: Nearly all vent-free gas appliances have manual or thermostatic controls that let the homeowner adjust the input rating to the preferred level of heating (e.g., low to high). Vent-free appliances come in a variety of sizes, ranging from inputs of 8,000 Btu to a maximum of 40,000 Btu. Smaller units are available for bathrooms (2,000 – 6,000 Btu) and bedrooms (10,000 Btu). Manufacturers provide clear sizing guidelines with their products.


Water Vapor Released By Vent-Free Appliances

Some people may be surprised to learn that vent-free appliances produce water. This occurs naturally by burning a combination of gas and air. The water is in the form of a vapor rather than a liquid. You can’t see it with your eyes.

During the cold months of the year, the relative humidity—the percentage of water vapor in the air—is low. You’ve probably experienced a scratchy throat caused by the dryness inside a home during the winter.

Health studies have shown that increasing the indoor relative humidity results in a reduction of respiratory illnesses. AHAM, the trade association for the humidifier industry, recommends a 60% indoor relative humidity.

To improve the level of human comfort and reduce symptoms like a scratchy throat, many people add humidification with either a portable or whole-house system. Of course, the water vapor added to the air comes not only from humidifiers but also from a variety of sources such as dishwashers, ranges, showers, etc.

Keep in mind that a home is not airtight. Even one built to the tightest construction standards allowed by codes still has at least 0.35 air exchanges per hour. This means the higher relative humidity indoor air is constantly being replaced by lower humidity outdoor air.

You’ve probably noticed cold air leaks around the windows and doors in your own home during winter. That’s indicative of air exchange taking place. While vent-free products increase the relative humidity, the air exchange decreases the relative humidity.

How does a vent-free appliance work in a really tight home?

The answer is “very well.”

It’s simple: a well-constructed home requires less heating, and as a result, the appliance will operate for a shorter period of time and produce less water vapor. Of course, in average homes—particularly those located in the most northern climates—you may notice some condensation on cold surfaces such as the inside of the windows. However, this condition is indicative of the weather and the construction, and most likely it would exist whether a vent-free appliance is present or not.

In summary, a vent-free appliance produces some of the water vapor that occurs in the home. It serves to help humidify the indoor air, and that’s beneficial for human comfort and health. Also, tight houses are superior for preventing condensation problems, making them good candidates for properly sized vent-free appliances.

The Oxygen Detection Safety-Pilot: A “CIRCUIT BREAKER” FOR GAS SUPPLY

Safety is built into every vent-free gas product. Every vent-free unit sold in the U.S. comes with a precision-engineered Oxygen Detection Safety- Pilot (ODS).

The ODS automatically reacts to a reduction in the room’s oxygen supply. If the oxygen level approaches 18%, the ODS shuts off the gas supply, eliminating any possibility of danger well before an unsafe level is approached. What’s more, the vent-free appliance can only be re-ignited manually, and only when the room air is back to normal.

According to ODS manufacturers, no documented deaths have been attributed to emissions from an ODS-equipped product. With more than ten million vent-free units operating in American homes and more than 50 million worldwide, that is an exemplary safety record.


Normal Operation:

20.9 Percent Oxygen – The flame touches the tip of the Thermocouple, generating the necessary millivoltage needed to hold the gas valve open.

Oxygen Level Drops:

19 Percent Oxygen – The flame begins to lift off the precision Pilot Burner. The Thermocouple begins to cool.

Safety Shutdown:

18 Percent Oxygen – The unstable pilot flame goes out, causing the Thermocouple to cool. The Thermocouple stops generating the electricity needed to hold the spring-loaded solenoid valve open. The valve shuts the vent-free gas heater down and cannot be started until the oxygen level in the room returns to normal.


To document how vent-free gas products affect indoor air quality, the American Gas Association Research (AGAR) Laboratories* performed an extensive, independent scientific study.

The study was performed in a real home, the AGAR research and demonstration house. AGAR scientists tested the levels of all five major contributors of indoor air quality – oxygen, carbon monoxide, carbon dioxide, nitrogen dioxide, and water vapor (humidity) – against the latest IAQ guidelines and recommendations.

The researchers concluded that, in all cases, vent-free gas heating products performed well within nationally recognized guidelines for indoor air quality. Vent-free gas products provide clean heat.

Innuendo vs. Fact-Based Research

From time to time, circulars have been disseminated that imply various indoor air quality concerns of ventfree gas products. However, none of the implications and assertions made in these publications have ever been supported by documented independent research. The AGAR study is documented independent research, substantiated by thorough and unbiased scientific testing. The AGAR research proved that vent-free gas appliances provide clean heat that meets or exceeds all nationally recognized guidelines for indoor air quality.

For an Executive Summary of the AGAR research study on indoor air quality with the use of vent-free gas products, call or write the Vent-Free Gas Products Alliance.

Jay Green
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