Gas Fireplaces

How to choose a gas fireplace

Start with venting, not with looks

Venting decides which fireplaces are even possible in your room, so it is worth settling before you fall for a flame picture. A direct vent unit is sealed off from the room: a coaxial pipe draws combustion air in from outside and carries exhaust back out through the same fitting. Nothing is taken from the room and nothing is released into it, which is why direct vent runs up to about 85% efficient, why it is safe in a tightly sealed modern house, and why it is generally permitted in bedrooms. It can vent horizontally straight through an exterior wall, so it does not need a chimney — the reason it dominates new construction and additions.

A vent-free unit has no pipe at all. It burns cleanly enough to exhaust into the room, which means essentially all of the fuel energy becomes heat and installation is as simple as a gas line. The trade-offs are real: it puts combustion byproducts and a significant amount of water vapour into the room air, every unit carries an oxygen depletion sensor, codes cap output against room volume, and many jurisdictions restrict or prohibit them outright — including in bedrooms and bathrooms. Check your local code before you buy one, not after.

A B-vent unit sits between the two. It draws combustion air from the room and exhausts vertically through a B-vent pipe or an existing chimney. Most of the heat goes up the flue, so nobody buys a B-vent to warm a room — they buy it for the tall, loose, open-hearth flame that sealed glass cannot quite reproduce.

Size the output to the room, and resist going bigger

A reasonable rule is 20 BTU per square foot in a well-insulated house and 30 in an older, draughtier one.

Oversizing is the more common and more expensive mistake: a unit with too much output ends up running on its low setting most of the season, which makes the flame look thin and wastes the premium you paid for the bigger firebox. If the fireplace is decorative and the furnace carries the real heating load, size down deliberately.

Decide how many sides you want to see

Single-sided is the straightforward case and covers most of this collection. A see-through unit is finished on both faces and opens into two rooms, which works beautifully between a living room and a dining room but costs you a wall and doubles the finishing work. Peninsula models show three sides, bay and corner models wrap the flame around a corner, and island units are visible from all four. Each step away from single-sided narrows your choice of models and raises the framing and finishing cost, so pick the configuration before you shortlist models rather than after.

Natural gas or propane

Most models here are offered in both, and on some brands they are ordered as separate units rather than converted in the field. Where a conversion kit is available it should be fitted by a licensed technician, because the orifice and pressure settings differ between the two fuels and getting them wrong affects both safety and warranty. Confirm which fuel you are ordering before the unit ships.

Measure the framing before you build the wall

Every built-in gas fireplace has a framed rough opening specified by the manufacturer — width, height and depth — plus clearance requirements to combustible material, mantel and hearth. Those numbers are not interchangeable between models, and depth in particular varies far more than the front dimensions suggest. Pull the framing dimensions from the installation manual for the exact model before any framing goes up, and give the vent run the same attention: horizontal runs have maximum lengths and minimum rises, and terminations have their own clearances to windows, doors, soffits and grade.

Gas fireplace FAQs

Does a gas fireplace need a chimney?

Usually not. A direct vent fireplace uses a sealed pipe that can run horizontally through an exterior wall, and a vent-free fireplace needs no vent at all, so neither requires a chimney. Only B-vent models need a vertical flue, which can be a dedicated B-vent pipe rather than a masonry chimney. If you already have a chimney and a firebox you want to keep, a gas fireplace insert is the product that uses it.

What is the difference between direct vent and vent-free?

A direct vent fireplace is sealed off from the room: it draws combustion air from outside and sends every byproduct outside, so it has no effect on indoor air and is generally allowed in bedrooms. A vent-free fireplace burns into the room, which makes it close to 100% efficient and simple to install, but it adds moisture and combustion byproducts to the room air, is capped by code against room volume, and is restricted or banned in some jurisdictions. Direct vent is the safer default in a tightly sealed modern home.

How many BTUs do I need?

Allow roughly 20 BTU per square foot in a well-insulated house and 30 in an older one, so a 30,000 BTU unit suits a 1,000–1,500 sq ft open-plan room. If the fireplace is there for atmosphere and your furnace carries the heating load, size down on purpose — an oversized unit spends the winter on its lowest setting, which produces a disappointing flame.

Will a gas fireplace work during a power outage?

It depends on the ignition. Millivolt and standing-pilot models use a thermopile powered by the pilot flame itself and will light and run with no electricity at all. Electronic ignition models need power, though many offer battery backup for exactly this situation. In either case the blower needs mains power, so you get radiant heat but no forced air. If outage performance matters to you, look for millivolt in the model description or confirm that the electronic model includes battery backup.

Is a gas fireplace cheaper to run than a wood fireplace?

For usable heat, almost always. An open wood-burning fireplace runs at roughly 5 to 15% efficiency and pulls heated household air up the chimney while it burns, so it can leave a house colder overall. A sealed gas fireplace delivers 70 to 85% of its fuel energy into the room as heat. Cost per unit of heat still depends on local gas and firewood prices, but the efficiency gap is wide enough that gas usually wins on heat delivered, and it wins outright on the work involved.

Can a gas fireplace be installed in a bedroom?

A direct vent fireplace generally can, because the sealed combustion chamber never takes air from the room or releases exhaust into it. Vent-free models are the ones commonly restricted or prohibited in bedrooms and bathrooms, and where they are allowed the permitted output is tied to room volume. Local code has the final say in both cases, so confirm with your installer before you plan the room around the fireplace.

Related collections

• Direct vent gas fireplaces
• Vent free fireplaces
• Outdoor gas fireplaces
• Gas fireplace inserts
• Majestic gas fireplaces
• Empire Boulevard linear gas fireplaces
• Electric fireplaces