Ventless Gas Fireplaces: What to Know Before You Buy

Ventless gas fireplace decorated with surrounding bricks, houseplants and couch

The Spruce / Ana Cadena

Even though few homes today rely on fireplaces as their primary heating source, many homeowners still enjoy the ambiance of a warm fireplace. Ventless gas fireplaces, in particular, are popular because they're clean and easy to use.

What Is a Ventless Gas Fireplace?

Also known as unvented or vent-free fireplaces, a ventless gas fireplace operates with natural gas or liquid propane (LP) that flows into a gas burner mounted in the fireplace. When ignited, the flames run through gaps in artificial ceramic fiber logs, giving the illusion of a real wood-burning fireplace.

The Importance of Venting

With any fireplace installation, a major issue is venting the exhaust gases, whether it is simple smoke from a wood-burning fireplace, or the exhaust fumes produced when you burn gas. Venting a fireplace is especially complicated in retrofit installations, where it can be problematic to find a route for the chimney flue. Another issue with fireplaces concerns the energy loss. Wood-burning fireplaces are inherently inefficient, since a good deal of the home's heat inevitably escapes up the flue rather than radiating into interior spaces. Vented gas fireplaces are somewhat better at retaining heat, but modern homes are now being built so airtight that even a vented gas fireplace may create negative air pressure that hinders good exhaust. Air flowing out a chimney vent flue can even prevent combustion gases from other appliances from exhausting properly.

For these reasons, both wood-burning fireplaces with traditional masonry chimneys and vented gas fireplaces are less prevalent than they once were. To solve these issues, a ventless gas fireplace might be the solution. Easier to install than vented wood or gas fireplaces and capable of warming small rooms, gas fireplaces that have no vents passing to the exterior are becoming more popular for remodeling work and even in new-construction homes. Because there is no airflow to the outdoors, they do not create the negative pressure problems that can occur with a vented fireplace. There are limitations, though.

Vented vs. Ventless Gas Fireplaces

In a traditional vented gas fireplace, there are two vents that run to the outside of the home. One is a fresh-air intake that provides combustion air help the gas burn more efficiently. The other vent safely removes any exhaust gases created by burning the natural gas or LP to the outdoors.

On the surface, a ventless gas fireplace looks quite similar to a vented fireplace. It has a control panel to operate the pilot light and flames, and holes in ceramic artificial logs for the flame jets. There is a slight difference to the flame jets between the two styles, and as a result, ventless fireplaces tend to burn somewhat less realistically than vented units. As with vented fireplace, ventless units usually have blowers that circulate air around the firebox to heat the room.

However, ventless fireplaces have neither of the two outdoor vents found in vented units. Instead, combustion air for the burner is drawn into the fireplace from the air inside the home, and exhaust fumes also remain inside the home.

This may sound dangerous, but ventless fireplaces are engineered in a manner that minimizes the exhaust fumes. A special regulator creates a fine mixture of gas and air that burns extremely cleanly, and the units are carefully tested in approved laboratories before they can be sold. Ventless gas fireplaces are deemed to operate within the range of safety for cycling these combusted gases back into the home's interior. By contrast, vented gas fireplaces create a dangerously high amount of combustion exhaust and therefore must be vented to the outdoors.

Are Ventless Gas Fireplaces Safe?

The safety of ventless gas fireplaces is a subject of debate. According to the National Association of Certified Home Inspectors (NACHI), a patchwork of regulations across the United States controls the legality of ventless fireplaces. Roughly a third of states allow these units with no restrictions. California is the only state that outright bans all ventless fireplaces, and there are notable restrictions in Massachusetts. In the remaining states, a welter of regulations controls ventless fireplaces based on factors such population of the city, altitude, and surrounding geography. In many states, there are restrictions on where the home you can install a ventless fireplace—they may not be allowed in sleeping areas, for example.

Low oxygen levels can be a concern with well-insulated homes that have a slow exchange of indoor and outdoor air. Ventless gas fireplaces have a feature called an oxygen detection system (ODS), which automatically turns off the unit if oxygen levels in the room fall below a certain level. The fireplaces may also have built-in CO (carbon monoxide) detectors that also automatically shut off the fireplace if high levels are detected. Still, hazards are present. Some manufacturers recommend leaving a window cracked open while running operating the fireplace to ensure there is a source of fresh air.

NACHI also observes that although fumes are greatly reduced, ventless fireplaces still release small amounts into the home, increasing the risk of carbon monoxide exposure. And non-vented burning of natural gas or propane also produces water vapor as a byproduct, which can increase humidity levels and the risk of mold.

It's therefore wise to do your homework on the units you are considering. Make sure its specifications meet safety standards, and that the unit is approved for installation by your building code authorities. Ventless fireplaces may well be a good choice for a decorative feature in a room where its use can be supervised, but shouldn't be used as a principal source of heat, especially in a sleeping area. And it is not a good choice if anyone in your home suffers from breathing problems, such as asthma or COPD.

Cost of Ventless Gas Fireplaces vs. Other Options

The cost of the firebox unit or insert and the log assemblies are roughly the same for both ventless and vented gas fireplaces. Both require the same type of natural gas or propane connection, so there is no cost difference in terms of plumbing. The cheapest way to have a ventless fireplace in your home is with a gel-fueled unit. No plumbing is required, as these units use alcohol-based gel fuel canisters that burn for up to three hours.

The major price difference between the two types of fireplaces is the cost of venting. Direct-vent gas fireplaces require two vents in the back: one that expels gases and another that draws in fresh air from the outside. (Some direct-vent fireplaces are vented with a single two-chamber vent pipe).

Because venting is such a large part of the installation cost, ventless fireplaces are generally a lot less expensive than vented units. A vented gas fireplace costs between $3,500 and $8,000 to purchase and have installed, depending on the amount of carpentry required to run the ductwork. By contrast, a ventless fireplace costs between $1,000 and $5,000.

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Article Sources
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  1. Ventless Fireplace Inspection. National Association of Certified Home Inspectors