Ventless Gas Fireplaces: Everything You Need to Know

At Total Home Supply, one of the products we specialize in are gas fireplaces. Of these, we often get inquiries about ventless gas fireplaces, and what makes them different from the vented kind.

To help out prospective customers and homeowners, we made this comprehensive guide on ventless gas fireplaces. We cover everything you might need to know, from their pros and cons, safety considerations, and regulations, to what to look for when selecting a ventless gas fireplace for your home.

What Is a Ventless Gas Fireplace?

A ventless gas fireplace, also known as a vent-free or unvented gas fireplace, is a heating appliance designed to produce warmth and ambiance without requiring an external vent or chimney. 

They produce heat by burning natural gas or propane using a high-efficiency burner system. These highly efficient burners generate almost complete combustion, greatly reducing harmful combustion byproducts like carbon monoxide. 

Unlike traditional vented fireplaces that direct combustion gasses to the outside, ventless fireplaces produce minimal emissions, which are released directly into the room. Since none of the heat escapes through outside vents, they release all the heat generated into the space, making them highly energy-efficient compared to vented fireplaces.

The Major Parts of a Ventless Gas Fireplace

Burner System: This is the core component where gas combusts, producing heat and flame. These highly efficient burners mix gas with just the right levels of oxygen to produce efficient and almost complete combustion, reducing emission levels.

Gas Valve: This controls the flow of gas to the burner. In some models, the valve can be adjusted to control flame height and heat output.

Ignition System: This ignites the gas, either through a manual spark ignition (using a pilot light) or an electronic ignition system. Some premium models use electronic ignition, which offers the convenience of remote or thermostat control.

Ceramic Logs or Fire Glass: These decorative elements mimic the look of traditional wood logs or add a modern flair with glass pieces. They are heat-resistant and designed to enhance the visual effect of the flames.

Thermostat (optional): Some ventless fireplaces have a built-in thermostat or a compatible thermostat control to regulate room temperature automatically. This is useful for maintaining consistent warmth without manual adjustments.

Flame Adjustment Controls: These allow users to adjust the size and intensity of the flames, enhancing ambiance and comfort. Not all models offer variable flame height.

Oxygen Depletion Sensor (ODS): The ODS is a critical safety feature. It monitors oxygen levels in the room and automatically shuts off the gas supply if oxygen levels drop below safe levels, usually around 18%.

Safety Shut-Off: Beyond the ODS, most ventless gas fireplaces include a secondary safety shut-off, which cuts off the gas supply in case of any operational issues.

Vented vs Ventless Gas Fireplace: What are the Differences?

Cost

Ventless: Generally cost less to purchase and install, since they don’t require venting. They are more affordable for homeowners looking for cost-effective heating without major structural changes.

Vented: Higher upfront costs for venting and installation, but they’re often favored for their realism, ambiance, and indoor air safety.

Ventilation and Installation

Ventless: Requires no external vent or chimney, making them easier and more affordable to install. They are ideal for rooms where it’s not feasible to vent outdoors, such as basements or apartments.

Vented: Require an external vent or chimney to expel combustion byproducts outside. They typically require more extensive installation, including vent pipes, but offer safer air quality.

Efficiency

Ventless: Highly efficient, as all heat stays within the room. This translates into lower heating costs and faster room warming, as 99-100% of the heat generated remains indoors.

Vented: Less as some heat escapes through the vent or chimney. However, they provide a more realistic flame effect, with some models achieving 70-85% efficiency despite the venting process.

Indoor Air Quality and Safety

Ventless: Since they release combustion byproducts like carbon monoxide and nitrogen dioxide into the room, they can affect indoor air quality, especially in tightly sealed homes. Ventless units do include an oxygen depletion sensor (ODS) to shut off the fireplace if oxygen levels fall too low, but air quality concerns remain, especially for individuals with respiratory conditions​. Ventless products should be used in spaces that are air sealed very well. 

Vented: By venting exhaust gasses outdoors, they are safer for prolonged use in smaller spaces, as they minimize the accumulation of combustion byproducts indoors.

Aesthetics and Realism

Ventless: Lack the traditional, open flame look because they must operate at specific combustion levels for safety, creating a controlled, lower flame. They often use ceramic logs or fire glass for visual effect, but the flame realism is usually secondary to vented models.

Vented: Provides a more realistic flame experience similar to traditional wood-burning fireplaces. The open flame is more dynamic and lifelike.

Maintenance 

Ventless: Require less maintenance, as they don’t have vent pipes or chimneys to clean. 

Vented: Maintenance is required for chimney or vent cleaning to prevent blockages and ensure efficient operation.

Legality

Ventless: Subject to local restrictions, with some areas and states banning them due to air quality concerns, especially in regions with strict indoor air safety codes.

Vented: Widely allowed without the same level of restriction, as they don’t affect indoor air quality directly.

Benefits of Ventless Gas Fireplaces

✔ High Efficiency

Ventless fireplaces are nearly 100% efficient since all the heat produced stays within the room rather than escaping through a vent or chimney. This efficient heat retention reduces energy costs, making ventless fireplaces cost-effective for heating small to medium-sized spaces quickly​.

✔ Easy Installation

Since ventless fireplaces don’t require a chimney or external venting, they are generally easier and less expensive to install compared to vented models. This flexibility allows for installation in various settings, such as apartments, basements, and rooms without access to an exterior wall​.

✔ Low Maintenance

Without the need for vent cleaning or chimney sweeping, ventless fireplaces require less maintenance than vented units. Regular inspection of components like the oxygen depletion sensor (ODS) is recommended, but overall maintenance demands are lower, which can save time and money in the long term.

✔ Versatile Placement

The absence of venting requirements allows ventless fireplaces to be installed almost anywhere within a home. They can even be wall-mounted or installed in areas with limited space, making them versatile options for modern interiors and compact living spaces​.

✔ Ambiance and Aesthetic Appeal

Many ventless fireplaces are designed to mimic the look of traditional wood-burning fireplaces, with ceramic logs or ember beds for visual effect. This allows homeowners to enjoy the warmth and ambiance of a fireplace without the mess, smoke, or maintenance associated with wood-burning units​.

✔ Environment-friendly

Ventless fireplaces produce fewer emissions than wood-burning fireplaces, and they burn fuel efficiently, which reduces the environmental impact. They operate on natural gas or propane, both of which are cleaner fuels that produce fewer airborne particles compared to wood smoke.

✔ Lower Operating Costs

Since ventless fireplaces operate without venting heat outdoors, they retain more warmth, often resulting in lower heating bills. Their energy-efficient design can significantly reduce the need for additional heating in the rooms they’re installed in, making them a budget-friendly option for supplemental heating.

Drawbacks of Ventless Gas Fireplaces

Indoor Air Quality Concerns

Since ventless fireplaces release combustion byproducts directly into the room, they can impact indoor air quality. Combustion produces gasses like carbon monoxide (CO) and nitrogen dioxide (NO₂), both of which can pose health risks, particularly in poorly ventilated spaces. 

Although ventless fireplaces are equipped with an oxygen depletion sensor (ODS) to shut off the unit if oxygen levels fall too low, this safeguard is not foolproof, especially in tightly sealed homes​

Increased Humidity and Risk of Mold

Ventless fireplaces release water vapor into the air, which can raise indoor humidity levels. Excess moisture can lead to condensation on walls and windows and, over time, can promote mold and mildew growth. In areas with high humidity, this added moisture can contribute to structural issues and degrade air quality even further​.

Less Realistic Flames

Ventless fireplaces are often designed with specific fuel-to-air ratios to minimize emissions, which can make the flames appear smaller or less natural than those in vented units. While some ventless models include ceramic logs and ember beds for visual effect, the overall flame realism may not satisfy those looking for the look of a traditional, open fire​.

Limited Run Time

To maintain air quality, many ventless fireplaces have recommended or even mandated maximum run times, often suggested at 4-6 hours or less. Prolonged use in enclosed spaces can lead to buildup of combustion byproducts and excessive moisture, so limiting use is generally recommended. This can restrict heating flexibility, especially in colder climates where extended use might be desired.

Room Size and Ventilation 

Ventless gas fireplaces are not suitable for all room sizes or types of homes. They work best in larger spaces with some level of natural ventilation, where combustion byproducts can disperse without causing a significant impact on air quality. Smaller, tightly sealed rooms may experience faster buildup of gasses, making ventless fireplaces less safe and effective in such spaces.

Not legal in some jurisdictions

Several regions in the US and Canada have restrictions or outright bans on ventless fireplaces. California and New York have banned ventless units in certain areas, while other states, including New Hampshire and West Virginia, have restrictions aimed at maintaining safe indoor air quality​.

Are Ventless Fireplaces Safe? Important Safety Features 

Due to their ventless design that releases combustion byproducts directly into the room rather than venting them outdoors, safety and air quality are the major concerns when using a ventless gas fireplaces. A common question that customers ask us is “Are ventless fireplaces safe?”

Thankfully, many ventless models incorporate safety features to minimize emissions and ensure safety in case of issues. Here are the three critical ones to look for:

Oxygen Depletion Sensor (ODS)

The ODS is a critical safety component that monitors oxygen levels in the room and automatically shuts off the fireplace if oxygen drops below safe levels. This sensor helps prevent the buildup of carbon monoxide and is an essential feature for ventless models​.

Safety Shut-Off Features

Beyond the ODS, additional shut-off features, such as high-heat sensors, are helpful for automatically turning off the unit if it begins to overheat.

Moisture and Humidity Control

Since ventless fireplaces release water vapor, some units offer features or settings to mitigate moisture buildup, which is crucial for reducing the risk of mold or dampness in the room.

Other Key Features to Look for in a Ventless Gas Fireplace

1. Electronic or Battery-Powered Ignition

Electronic ignition provides easy and quick lighting and is often more reliable than traditional pilot lights. Some models also offer battery-powered ignition, ensuring the unit can function during a power outage.

2. Thermostatic Control

A built-in thermostat or remote thermostat allows for more precise temperature control, adjusting heat output based on the room’s ambient temperature. This feature can improve energy efficiency by preventing the fireplace from overheating the room​.

3. Variable Flame Control

Adjustable flame settings allow you to control the intensity and height of the flames. This customization adds to the ambiance and helps manage heat output based on personal comfort levels.

4. Automatic Shut-Off Timer

An automatic timer is a convenient safety feature that can turn off the fireplace after a set period, preventing unnecessary fuel consumption and reducing safety risks if you forget to shut it off manually.

Other Considerations

Aesthetic Features

Consider the design elements like ceramic logs, fire glass, or ember beds, which contribute to the fireplace’s appearance. These features mimic the look of real wood-burning fireplaces and add to the overall ambiance.

Remote Control and Smart Connectivity

Many ventless gas fireplaces now come with remote control functionality, allowing you to adjust the flame, temperature, and ignition from a distance. Some models also support smart home integration for easier management through mobile apps​

Our Recommended Ventless Gas Fireplaces

1. Entry level

Monessen BUF32-A 32″ Vent-Free Exacta Firebox with Clean Face and Painted Interior

This firebox can be installed into a pre-existing wood-burning fireplace that has been converted with a gas line or into your wall, in either a flat wall or corner installation. With zero clearance, the firebox can be installed flush against any surface like drywall or wood. It can accept 18″ vent free burners and log sets (sold separately).

It offers a clean louverless face and a large 32″ x 27″ viewing area, with a black interior that provides a contemporary background for your log set. The safety screen can be tucked away into hidden side pockets offering a full, unencumbered view.

2. With smart connectivity

Monessen LCUF36CR-GT 36″ Vent-Free Lo-Rider Clean Face Firebox with Grey Multi-tonal Traditional Stacked Interior Panels

This low-profile firebox can accept most 24″ and 30″ vent free log sets and looks as if the flames come almost from floor/ground level. 

Besides the low profile and extra large viewing area, this firebox is zero clearance and includes a black hood and standard refractory firebrick liner. The look can customized with a wide range of optional trim kits and facings.

Additionally, Monessen offers Natural Blaze burners with Natural Blaze Technology. This technology helps provide taller, more lively flames for a truly realistic fire in your vent-free firebox. Beautiful yellow flames are instantly achieved every time your burner is switched on. Available burners for the 36″ firebox include:

Millivolt Valve (NB24PV, NB24NV) – standing pilot with on/off switch and manual variable flame height control  and remote ready (remote sold separately)

Electronic Ignition with Intellifire Plus System (NB24PIF, NB24NIF) – intermittent pilot/electronic ignition, 3 step flame adjustment and Touch Screen Thermostat Remote included.

3. Multi sided:

White Mountain Hearth VFP36PB2E 36″ Breckenridge Vent-Free 3-Sided Peninsula Firebox

This 36” Peninsula vent-free firebox can be installed between two adjacent rooms with an appropriately built frame. Since no venting is required, you can add a multi-sided firebox between almost any 2 rooms. It does not need to be installed on an exterior wall as long as there is a gas line. It is compatible with any 18″, 24″ or 30″ Slope Glaze Vista Burner with either Stone River or Rock Creek Log Sets.

A 30″ Vista Slope Glaze VFSUR Millivolt Burner or 30″ Intermittent Pilot Burner is available. The burner can be installed in a vented or vent-free application. When used in a vented application, it is only certified to be used as a decorative gas appliance and cannot be operated with a remote. Your installer must block the fireplace damper partially open. A damper clamp is included for this purpose. The Vista Slope Glaze VFSUE Intermittent Burner is also available and includes a remote.

Ventless Gas Fireplaces FAQ

Do ventless fireplaces work during power outages?

Yes, many ventless gas fireplaces can work during power outages, but it depends on the ignition system and any additional power features they may have.

Many ventless models use a battery-powered ignition system or a millivolt valve that doesn’t require power. These use a thermopile that generates a small electric current from the pilot flame. 

Some ventless fireplaces also have electronic ignitions that require electricity to start, but they may include a battery backup. During normal operation, the fireplace uses electricity, but if the power goes out, the battery takes over to start ignition.

Some ventless models may also have blowers or fans that need electricity to circulate heat effectively. Without power, the fireplace will still generate radiant heat, but it won’t disperse as evenly throughout the room.

Can they provide sufficient heat for large rooms or open areas?

Ventless gas fireplaces can provide sufficient heat for moderately sized rooms, but they typically aren’t ideal for heating large rooms or open areas effectively. Here’s why:

☑ BTU Output

Ventless gas fireplaces are generally designed to heat rooms of about 1,000 to 1,200 square feet, depending on their BTU rating. Typical ventless fireplaces range from 5,000 to 40,000 BTUs. While a unit with 30,000 BTUs might adequately heat a large living room or medium-sized space, it may struggle in more expansive areas or open-concept layouts where heat can disperse quickly​.

☑ Heat Distribution Limitations

Ventless fireplaces heat primarily through radiant and convective heating, which works well in smaller, enclosed areas. In larger, open spaces, however, the heat is less contained, so warmth dissipates more readily. 

Additionally, most ventless fireplaces don’t have built-in fans or blowers, and those that do require electricity, which may limit heat circulation in power outages​

☑ Room and Usage Restrictions

Ventless fireplaces are limited by air quality considerations, as they release combustion byproducts into the room. In large or open areas, more fuel might be required to reach the desired temperature, potentially increasing these byproducts. This can lead to higher humidity and possible air quality issues, particularly if the unit is used for extended periods​.

☑ Supplemental Heating Solution

For large rooms or open spaces, ventless fireplaces are often best used as supplemental heating rather than primary heat sources. In smaller rooms, they can indeed act as the primary heating source, but their effectiveness diminishes in large or open-plan areas where additional heating might be necessary.

Your Expert Source for Ventless Gas Fireplaces

Over the years, we’ve helped many homeowners choose the right ventless fireplace for their home. We carry a wide range of ventless gas fireplaces to suit different needs and budgets, including single-sided, multi-sided, or built-in versions. We even offer expert advice to ensure that our customers are satisfied with the ventless model they choose.

Give our selection a look and enjoy the efficient and cost-effective heating of a ventless fireplace, with none of the worries and cleaning headaches of a traditional or vented fireplace!