Venting Explained

There are certain hearth products, such as electric or vent-free appliances, that are designed not to require any venting to the outdoors. But all other fireplaces, stoves and inserts—whether their fuel source is gas, wood or pellets—rely on some type of venting to circulate fresh air inside, and to ensure that harmful combustion byproducts are removed from a home’s indoor air.

It sounds relatively straightforward, doesn’t it? What’s complex is that there are multiple ways to vent a fireplace—sometimes even several methods for one category of hearth structure, each with its own benefits and school of thought behind it. Understanding what method of venting is preferable for your your home helps you make an informed selection and makes the process of researching, buying, building or installing your hearth product much less daunting.

“The fireplace solution that’s right for you and your home is very much tied to the venting capabilities that exist,” says Julie Milum, vice president of the fireplace category and the Heat & Glo brand at Hearth & Home Technologies. “Fire is fire. It requires oxygen; it expels carbon dioxide—and venting is a part of all of it.”

There are several ways to route venting for fireplaces, stoves and inserts, and the direction and logistics often depend on the type of hearth product and the fuel it burns. Read on to learn more about fireplace venting technology and requirements, and to find out what the experts recommend when it comes to selecting a perfect-fit hearth product.

Venting A Gas Fireplace to The Outside

Gaining in popularity since the middle of the 20th century, natural gas is the fuel responsible for the largest portion of home space heating in North America, according to an analysis of several studies completed by James E. Houck, Ph.D, a consultant in energy, biomass and the environment, that was published in a 2017 issue of Hearth & Home magazine.

Gas fireplaces can be vented one of three—technically two—ways:

Direct vent technology: A sealed combustion system protects indoor air quality by drawing outside air for the fire and expelling 100 percent of combustion exhaust and byproducts outside the home.

B-vent or “natural” venting technology: This system is not sealed; it draws air from a room into the combustion chamber and exhaust must be routed through the roof via a pipe.

Vent-free or ventless technology: This method actually relies on a higher burn temperature—rather than physical venting like in the cases of direct vent or B-vent—to rid the air of combustion byproducts.

Direct vent is by far the most common venting method and is the newest form of venting, invented by the founders of Heat & Glo in the 1980s; it remains a popular choice because of its efficiency, safety, flexibility and the fact that it does not require an existing chimney.

Direct Vent Fireplace Venting

To understand how direct vent works, it’s important to first become aware of the importance of airflow in a hearth unit.

In a direct vent gas appliance, fresh air is drawn from the outdoors into the hearth unit, and expelled air is sent outside via a flue system that terminates outside. Most direct vent gas fireplaces are vented to the outdoors horizontally (through the wall), but they can also be routed vertically (through the roof).

To vent the fireplace, a pair of rigid flues nestled inside one another—called a coaxial unit, since they both share an axis—is installed in sections ranging from 4" to 48" in length, with 90°- and 45° angled elbows that allow for flexibility with placement. A 4" inner flue is surrounded by an outer flue that is either 6 5/8" or 8" in diameter.

As the gas fireplace is started, explains Chad Hendrickson, director of product development for Hearth & Home Technologies, Heat & Glo’s parent company, exhaust travels through the inner pipe to the outdoors, while the outer pipe allows the fresh air for combustion to come in and be transmitted directly into the bottom of the sealed firebox, where it ignites the unit. The outer pipe also helps insulate any surrounding combustible components from heat traveling through the system. Most coaxial systems connect to the fireplace unit in a direct vent fireplace chase — the insulated structure that houses the fireplace.

The direct vent fireplace unit itself is sealed off from the home’s interior with a high-temperature glass panel, so any flames or combustion byproducts are completely separated from the air in your home. “Everything is done through the pipes; the fireplace is not taking any airflow from inside your room for combustion,” says Hendrickson. “A direct vent appliance draws its combustion air from outside and the vent exhausts the combustion fumes to the outside as well—it does that all through the direct vent pipe.”

Direct vent gas fireplaces and inserts produce highly efficient heat in a broad range of sizes and can be installed almost anywhere in the home. In fact, they are the most requested type of hearth system by U.S. consumers today. Given the venting flexibility, wide range of styles and the fact that a chimney is not required for installation, direct vent appliances are well-suited to just about any type of home and room.

Among its many other benefits, “Direct vent technology gives you the flexibility to really install your fireplace anywhere,” says Hendrickson.

Direct Vent Through the Wall Vs. Through the Roof

Venting a gas fireplace to the outside essentially boils down to a simple question: “Up or over?” But the selected location in the home, as well as the existence of a masonry chimney and the home’s exterior structure, all factor in to this decision.

Horizontal Direct Vent

Venting horizontally—through a wall—is a simple solution, ideal in cases where a gas fireplace is being installed on an exterior wall. Venting can be as easy as running pipe from the back of the fireplace out through the wall, then installing a termination cap.

“If I put an appliance on my exterior wall, I can go right off the back, basically put a cap on and not have to worry about extensive venting going up in the roof,” Hendrickson says. “So it will save on overall installation time as well as installation cost.”

Before committing to venting a gas fireplace horizontally, though, Hendrickson suggests considering where exactly the flue’s termination cap will be. “Let’s say I’m venting through an exterior wall on my house. On the backside of the wall, where is the cap going to be? At what height?” He also points out that there will be noises from the cap filling as well as combustion fumes that will emanate from the cap—something you may not want happening right on your deck or patio when you’re entertaining outdoors. A hearth dealer will walk you through vent system safety and gas fireplace venting requirements such as proper clearances around the cap. (For example, the cap should not be located in a place where it could be rendered inaccessible by snow.)

Vertical Direct Vent

Vertically venting a gas fireplace through the roof is a little more cost- and labor-intensive, but necessary if a homeowner is looking to vent a gas fireplace on an interior wall—or when a gas fireplace insert is being installed and a masonry chimney, through which venting will run, already exists.

Power Venting

A technology called power venting can help make a direct vent fireplace work even more efficiently, especially in cases where a venting system’s natural airflow is not moving enough air for the fire, or in situations where a fireplace needs to be vented down. This fan-powered accessory that pulls air through the venting system can be installed either in the venting itself or at the termination cap on the exterior of your home. It allows venting to zigzag throughout your home—up, down, over or under—making it possible to install a gas fireplace virtually anywhere.

How Direct Vent Technology Began

Direct vent is the largest market segment to date in the hearth industry in terms of dollars—and it’s likely currently approaching the largest segment in units, according to John Shimek, senior vice president of product development for Heat & Glo. Yet it’s still a relatively young technology.

Shimek’s father, Ron Shimek, and uncle Dan Shimek—an engineer and research chemist, respectively— founded the Heat & Glo brand in Ron’s garage in 1975. The brothers pioneered direct vent gas technology in 1987 and their invention has since revolutionized the way fireplaces operate. John Shimek recalls that as far back as the early ‘80s, his family began experimenting with gas direct vent technology as an alternative to the wood-burning fireplaces for which Heat & Glo was already known—a product that, at the time, could be costly and messy to install and maintain.

“My dad and his brother started playing with this gas direct vent technology literally in our basement and garage,” explains Shimek. “They started tinkering with a sealed combustion system based on the physics of hot air rising and flowing. If they made it airtight, the air exhausting, because it’s heated, would bring air in on the combustion side.”

According to Shimek, a commitment to “efficiency, convenience and safety” is what drove Heat & Glo’s direct vent innovation and took it from a garage tinker project to the cutting-edge technology we know today.

The brand’s momentum hasn’t slowed, either. Direct vent has been named by the Energy & Environmental Building Association as one of the top 25 technology breakthroughs in residential construction and has become a staple in new home construction. Ever the pioneer, Heat & Glo is the most award-winning U.S. fireplace brand and has been granted more patents than any hearth manufacturer.

“We’ve maintained our leadership position and innovation, and made sure that consumers get what they want,” he says. “There are still a lot of wood-burning boxes that are sold but, by and large, the direct vent fireplace is the go-to fireplace for new home construction.”

Direct Vent Air Quality

According to the U.S. Environmental Protection Agency (EPA), homeowners are increasingly concerned about indoor air quality, which, if compromised, can trigger respiratory ailments like asthma. The EPA also acknowledges that indoor pollution sources that release gasses or particles into the air are the primary cause of air quality problems in the home. Insufficient ventilation can increase indoor pollutant levels by not circulating enough outdoor air to dilute emissions, and by not carrying indoor air pollutants out of the home. For these reasons, direct vent technology is an American Lung Association Midwest Health House® program Clean Air Choice™.

Hendrickson maintains that air quality is the biggest benefit to installing a direct vent gas fireplace. Since the unit is a sealed system, “it has no effect on the inside air quality of your home,” he says. “You’re venting 100 percent of the combustion fumes to the outside, and you’re taking 100 percent of the combustion air from outside air as well. So you’re not off-balancing any air quality in your home.”

Are Direct Vent Fireplaces Safe?

Above and beyond the built-in safety features of gas fireplaces—such as safety screens, inspections and carbon monoxide detectors—direct vent models have valves that control the gas flow to the fireplace. When the pilot light goes out, the gas turns off. You can rest easy knowing that the gas will never build up and create an unsafe environment in your home in case of an outage.

Direct Vent Gas Fireplace Efficiency

Did you know that a gas fireplace or fireplace insert could help reduce your heating costs? Similar to the premise of a hybrid car, you can turn down your home’s thermostat and “zone heat” the rooms you use most with an efficient gas fireplace. It cuts down on the fuel consumed by your furnace and can help reduce home heating bills by 20 to 40 percent, according to the Hearth, Patio and Barbecue Association.

With a controlled pilot light and temperature system, homeowners tend to use less gas with a direct vent gas fireplace. While specific costs vary based on location, utility and fuel type, national averages to run a natural gas fireplace that consumes approximately 27,000 BTUs/hour will cost less that 20 cents per hour to enjoy. Adding to that efficiency, says Hendrickson, is that no air from your home is escaping up the chimney.

Direct vent gas technology is the preferred technology in every green building program, including the National Association of Home Builders Green Home Building Standards, U.S. Green Building Council LEED® for Homes and ENERGY STAR’s® Indoor Air Package.

Venting a Gas Fireplace Insert

Gas fireplace inserts are a way to modernize a home and transform a wood-burning fireplace into a convenient, efficient, easy-to-maintain gas fireplace that turns on with the flip of a switch—just like a direct vent gas fireplace. Venting for fireplace inserts varies depending on the fuel type, but gas inserts are vented similarly to gas fireplaces—typically vertically, through the existing masonry chimney—but done so colinearly rather than coaxially.

“If you’re dealing with an insert, you’re likely dealing with converting a wood fireplace to gas,” Hendrickson explains. “You have to be able to run something down the system flue that you already have.” Instead of connecting sections of coaxial direct vent pipe in a small cavity where they may not fit, a colinear system allows some wiggle room. Two flexible 3” aluminum liners—typically installed in one long piece rather than in sections—run parallel to each other, one for fresh air to come in and one for exhaust to go out. “They can expand, they can become compressed and you can extend them to the length you need,” Hendrickson says.

With collinear venting, the fireplace insert unit is also sealed off from your home just like a direct vent gas fireplace would be. “They are still direct vent systems, so they’re a sealed system and they’re taking exhaust 100 percent to the outside and taking fresh air from the outside as well. The difference is the pipe—the colinear system,” says Hendrickson.

Venting a Gas Stove

Venting a gas stove uses the same direct vent process (horizontally through a wall, or vertically through the roof) as a direct vent gas fireplace or insert, meaning you can place a gas stove almost anywhere in your home.

Unlike a direct vent appliance, a B-vent appliance isn’t a sealed system, so it draws combustion air from the room into the combustion chamber. Exhaust then goes out through the roof via a single double-wall pipe, the outer layer of which acts as a heat insulator. A B-vent gas fireplace must be vented vertically, though, as it relies on the natural buoyancy of combustion gasses to make their way out of the home, thus its other moniker, “natural vent.”

B-vent fireplace units and venting systems tend to be smaller and require less of a footprint in the home, making them an option for smaller rooms. Installation is somewhat straightforward; however they have less venting flexibility and the need to vent vertically could pose challenges in some homes.

“In those cases,” explains Hendrickson, “you’re going to probably spend a little bit more on installation costs as well as venting.”

How Vent-Free Gas Fireplaces Work

With venting being such a crucial piece to the fireplace puzzle, a vent-free appliance might sound like an oxymoron. But these marvels of the hearth world are in a class all their own, thanks to modern spins on tried-and-true heating methods that date back to the 1800s.

They are called vent-free “literally because they do not require any venting,” explains Lara Usilton, director of brand marketing for Monessen, which specializes in vent-free gas fireplaces and other hearth products. “That means there’s no chimney, no flue, no pipe.”

A vent-free fireplace is an open system that takes in room air for combustion. Instead of routing the resulting gasses to the outdoors, though, a vent-free appliance operates at a high enough temperature to essentially burn up any combustion byproducts before they can go back into the air, eliminating the need for venting altogether. These self-contained appliances are “incredibly efficient,” says Usilton. Because no air escapes through venting, Usilton estimates that for every dollar that the owner of a vent-free gas fireplace spends on heat, 99 cents is retained.

While some may be hesitant to install a vent-free fireplace because of the lack of venting, vent-free fireplace technology has many benefits. Usilton says that this method is safe and sound—and has come a long way from the rudimentary heating process that originated in Europe and the United States about 80 years ago.

The category as we know it today was refined in Europe in the 1950s and became more popular in the United States in the ‘80s with the addition of modern safety mechanisms. Although vent-free fireplaces are prohibited in some states and municipalities out of concern for indoor air quality in certain types of houses, Usilton points out that independent studies show a vent-free fireplace burns so efficiently, no more moisture is found in a room with a vent-free hearth than in a vented one. Thanks to updated testing requirements and safety regulations, Usilton adds, to date vent-free fireplaces have a zero-percent failure rate with the Consumer Product Safety Commission.

In addition to saving money on fuel, a vent-free fireplace typically is less expensive and easier to install than a vented model and can be located in hard-to-vent places, such as an interior or below-grade wall. In as little as two hours, a technician can drop the fireplace into a decorative cabinet, hook it up to an existing gas line and go—no venting, ductwork or renovations needed.

Vent-free products are known for abundant heat, Usilton adds. “They’re fantastic options as supplemental heat. In winter, if you ever have a winter power outage, you don’t have to worry about being cold.” She points out that these models are extremely popular in warmer climates such as the southeast United States. “You might turn your vent-free product on in the morning just to take the chill off in the fall or late winter. Then you don’t have to turn the furnace on for a lot longer.”

Wood-Burning Fireplace Venting Options

There’s something especially cozy and rugged about a wood fireplace, stove or insert. Heat & Glo wood-burning fireplaces bring a one-of-a-kind charm and ambiance to any space. While today’s wood-burning fireplaces are infinitely easier to install and maintain than those of yesteryear, there can be some limitations when it comes to venting these appliances.

Wood-burning hearths must be vented to the outdoors vertically, through a home’s roof. This process involves construction through the roof and finishing the interior and exterior of the home once the hearth is installed. First, the fireplace box is surrounded by non-combustible board, framing and a header. A metal vent pipe is then routed from the fireplace through a flue and chimney liner installed within the walls of an existing masonry chimney, then the liner is topped with a vertical termination cap.

Venting a Wood-Burning Stove

Venting a wood-burning stove is similar to venting a wood-burning fireplace in that it also requires a Class A chimney that vents vertically and terminates over a home’s roof line. But since a standalone stove is a closed system (much like a direct vent gas fireplace, it does not pull in room air but requires fresh air to be drawn in from outside), it vents through a ventilation pipe in the chimney, whereas a wood-burning fireplace only requires a chimney liner. A pipe connects the firebox to the chimney and works to release smoke and draw fresh air. Smoke will exit the firebox through the ventilation pipe and chimney. At the same time, the firebox will draw in fresh air through the chimney and ventilation pipe.

Venting a Wood-Burning Fireplace Insert

If you’d prefer to update your wood-burning fireplace but keep heating with wood, a wood insert can transform your fireplace into a heating powerhouse. Wood-burning inserts use a stainless steel, flexible single wall liner up the existing chimney to termination.

Pellet Stove and Pellet Insert Venting

For DIY-savvy homeowners, a pellet stove—which burns compressed wood or biomass by steadily feeding it from a hopper into the stove’s burn pot area—are a low-cost, low-maintenance home heating method. Since they rely on renewable energy, there is less concern about the variation of fuel costs; pellet stove tax credits and rebates may even be available because of their efficiency.

Pellet stove venting differs from both direct vent gas fireplace venting and wood stove venting. Products such as Harman Stoves, PelPro and Quadra-Fire pellet stoves can be vented through an existing chimney. But, unlike wood stoves, they do not require a chimney for venting and can easily be vented through a side wall by the homeowners themselves (with the help of a robust user’s manual and the manufacturer’s how-to resources, of course). Pellet-burning stoves are vented using a pressurized hybrid system with a stainless-steel inner wall and gaskets to seal tightly, while pellet inserts use a hybrid stainless steel vent system. The easy installation and minimal maintenance allows for incredible flexibility and savings.

What To Know Before You Build

Now that you’ve graduated Venting 101, here comes the exciting part: Selecting the perfect hearth that doesn’t just warm your home but suits your family’s needs and fits your interior design aesthetic. Whether you want a fireplace for an existing or yet-to-be-built home, hearth experts recommend thinking about these important factors when deciding which fireplace, stove or insert is right for you.

Where You Want to Put Your Hearth

“The biggest thing is making sure that you pick where you want a fireplace to be,” he says. “Although it might look really good in the spot that you want it, you may or may not be able to vent it there. Depending on the size of the pipe that has to be run, can it fit in that space? How far does it have to run? What are the parameters around the direct vent?” Hendrickson notes, for example, that with most direct vent appliances, up to three elbows and 40 feet of flue pipe can be used in order to avoid exhaust struggling to get out of the house. “Where I want to put that fireplace, can I get to an outside wall, or can I get up through the roof?”

Beyond the room (or rooms) where the fireplace is located, trends in wall placement also are evolving. Modern-style fireplaces are often placed higher on the wall, like a piece of art. “As you’re trying to plan where you want your hearth, there are lots of options out there that impact the hearth quite a bit,” Milum says.

What Purpose Your Hearth Will Serve

All the experts agree: Being decisive about your fireplace’s purpose will help you find your home’s perfect match—and will save you a lot of time in the long run.

Usilton recommends asking yourself a few questions early on in the process: “Will it heat your home or just look pretty? Do you want heat or do you want ambiance—or do you want both? How much do you intend to use it? “

Usilton also urges those researching hearth appliances to consider geography. “Do you want a product that you’re using to literally heat your home like a wood stove, which are very popular in the Northeast? Or do you want something where every now and then you might need to take the chill off?” she says. “Another option is if want something that’s there as an emergency heat source in the case of a winter power outage.” After all, a family in a Georgia climate may have a much different use for their hearth appliance than one living in a home in Maine, Arizona or the Pacific Northwest.

“When you go to a warmer climate, naturally people are a little less interested in heat output,” Milun adds. “Whereas say, in the state of Minnesota, people want that heat output. There are larger fireplaces with higher BTUs that are known to put out a lot of heat that perhaps aren’t the best options in places like Arizona and Florida.” Community infrastructure, such as gas utility availability and local housing styles—think typical room size and the age of a home—will also come into play.

“Often people think, ‘a fireplace is a fireplace’ and that’s not at all true,” Usilton says. “There are very different applications and different features and functionality.”

Consult the Experts

Safety is of course key, and Heat & Glo is committed to that value. John Shimek knows, as his family founded the company, which has been a leader in the hearth business since 1975. Shimek advises picking a well-known brand—“a company with enough scale to do the proper design, engineering and testing to make sure you have a safe appliance. Pick a reputable manufacturer that has the scale to make sure it’s a safe product.”

“What I think we do better than most is make sure that our products are tested above and beyond even the Underwriters Laboratories or American Gas Association labs,” he adds. “We make sure that our products are safe.”

While online research about fireplace characteristics and installation is incredibly valuable, Usilton says, there’s no substitute for talking to a knowledgeable dealer—either on the phone or in person at a showroom—to help guide you through the process.

“I think it’s really important when you’re buying a product like this that is a major investment in your home, and actually adds value to your home, to go visit a hearth dealer,” she says. “Find an expert, go visit a store and get questions answered one-on-one. That can really help guide you to the best solution for your particular situation.”

Learn More

Fireplace venting is a vast topic with seemingly endless options, but with a little research, some technical forethought and an open mind, your dream hearth product is on the horizon.

Find more information at your nearest Heat & Glo licensed dealer, or dive right in to explore Heat & Glo’s selection of direct vent gas fireplaces, inserts, and wood fireplaces for any home.