Fireplace Venting Options

While chimneys have been discussed separately in the Fireplace Guide, there are many other types of fireplace venting systems to consider. Venting depends on environmental and climatic conditions, altitude, type of fireplace and fuel and other factors.

Proper fireplace ventilation affects the heating efficiency and safety of your fireplace. The correct choice and installation of a fireplace venting system requires an understanding of the options and techniques involved when installing or updating fireplace venting. This is doubly true when converting a wood-burning fireplace to gas or pellet fuel types.

If updating an existing fireplace or retrofitting a new fireplace in an existing home, you may have limited venting options due to the desired placement of the fireplace, local building codes and regulations and the type, design and style of the fireplace.

Fireplace and Wood Burning Stove Venting

Generally speaking, a natural wood-fueled fireplace uses a masonry or stud-supported metal chimney to vent combustion air outside, over the top of the roof; the vent should be three feet above the roof or at least two feet taller than any structure located within a ten foot radius.

The stovepipe of a wood burning stove serves the same purpose but may be exposed if it runs directly from the stove to the roof opening through which it extends. This significantly reduces costs versus building a chimney structure. Gas B-Vent fireplace venting systems also work off this “stovepipe” concept.

Either a brick and mortar masonry or a Class A type all-fuel chimney system is needed to properly vent most real wood-burning fireplaces.

Venting a Pellet Burning Fireplace

Pellet-burning fireplaces require a mechanical exhaust system, with a fan designed to forcefully pull the combustion gases and by-products out of the unit. A flue is needed as with wood-burning fireplaces; although the design may vary from a traditional chimney flue depending on the unit and whether you are installing a new fireplace versus converting a wood-burning fireplace.

Gas Fireplace Venting Systems

A gas vent pulls air into the firebox to be combusted and also emits exhaust; where the air comes from and where it exits is largely a function of the venting system, which is specified based on the unit itself.

With gas, there are a variety of types and designs, so venting depends on whether the gas fireplace unit is B-Vent, Direct Vent or Ventless:


In a “B-vent” system, combustion air is drawn from the firebox and vented outdoor through an economical pipe instead of a chimney (the B-Pipe of course). Features and advantages of a B-vent include:

  • Inexpensive and easier to install since a full chimney is not needed; less expensive than direct venting.
  • Zero clearance to combustibles.
  • Draws air from inside the home for combustion and vents above the roof like a furnace or regular chimney.
  • Fireplaces look like traditional wood-burners and come in a wide range of sizes, styles and options.
  • Less restrictive placement of the fireplace; can go anywhere the B-Vent can be installed.
  • Due to changes in regulations and building codes related to fireplaces, many builders install either B-Vent or Direct Vent fireplaces now instead of the traditional wood-burning fireplace with a gas starter.

Direct Vent

A direct vent system draws air from outside into the combustion area of the fireplace unit and vents combustion air back outside. No chimney or B-Vent is required! These units are very efficient at heating your home, do not affect the air quality inside the living space and are less expensive than most vented fireplace systems.

Direct venting varies from one manufacturer and model to another, but a coaxial pipe system is commonly used; small inner pipe vents combustion air to the outside of the home while the larger outside pipe draws fresh air into the fireplace. Pretty slick! Characteristics and benefits of direct venting include:

  • Can be vented out the top or the back, depending on installation needs.
  • Can be vented horizontally through the outside wall or vertically through the roof without needing either a chimney or B-Vent.
  • Direct vent fireplaces are an efficient way to heat a room and most are rated as gas wall furnace units.
  • As with B-vent units, direct vents are zero clearance to combustibles.
  • Easy to install and saves space; some units are designed so that you can custom design the surround, hearth and mantel as you would a more traditional fireplace unit. Others are available with options such as the hearth, surround and/or mantelpiece, all designed for simple installation.
  • With an enclosed front, the characteristics of a direct vent fireplace makes it well suited to buttoned-up, modern homes with tight seals and plenty of insulation.

Vent-Free or Ventless

When even a direct vent fireplace is not appropriate, you can use a ventless unit if all else fails. These fireplaces are unique in that air is drawn from inside the house into the combustion area and vented back into the home after combustion! This is enabled by a design that burns gas very cleanly that the only by-product flowing back into the living space to be concerned with is carbon dioxide (water).

While there were once concerns about the emissions into a home’s living space with direct vent fireplaces, direct vent technology has continued to improve as a very viable option to installing a fireplace in a home or room where previously no other real options exist!

The main combustion by-products from ventless units that might affect living space air quality include:

  • Carbon monoxide
  • Carbon dioxide
  • Nitrogen dioxide
  • Oxygen
  • Water vapor (humidity)

Of these, the main by-product to be worried about is the last (humidity); a ventless fireplace can introduce up to a gallon of water for every four hours the unit is in operation. Allergens and dander from humans and pets will be carried through the system, so people with severe allergies may be of concern when choosing a ventless system.

Since there is no chimney, flue, B-vent or a even coaxial pipe with which to be concerned, a vent-free fireplace can be installed in almost any location in the house. Characteristics and benefits of vent free include:

  • Affordable to purchase and operate, up to 99 percent energy efficient
  • Most do not require an electric fan, so they can operate even during a power outage.
  • Burn clean and relatively cool at 40 thousand Btu per hour of heat output.
  • Clean and safe, but should be installed along with a carbon monoxide detector; you really ought to have them in your home regardless!
  • Different models can run on either natural or liquid propane gas.
  • Not good in cold, damp climates, where increased moisture and humidity can be a problem if you use a ventless fireplace regularly; this can be a problem if you are in a “wet state” like Oregon, where I live.
  • Blue or yellow flame burner or ceramic plaque burner may not always produce the most realistic appearance of a wood fire; varies from model to model.

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