Understanding Fireplace Inserts

If you are looking to install a fireplace insert, just a little bit of research will show you just how many options you have.  Fireplace inserts are all similar, but they are built for vastly different purposes.  This article provides a general definition for a fireplace insert and specifics about a few different types of inserts. By the end, you’ll understand the differences between them.

What are fireplace inserts?

Fireplace inserts are self-contained units designed to fit smoothly within a pre-existing masonry fireplace, a wall, or a frame.  Some inserts are ventless. Others vent through direct venting or an original chimney. Fireplace inserts are also far more energy efficient than masonry fireplaces, which leads to a smaller carbon footprint and more heat.  Designers build fireplace inserts to burn a specific fuel type. So inserts, depending on the fuels they burn, will have different properties.

Most people install a fireplace insert into a pre-existing masonry fireplace. (For some inserts, you will also be able to build a frame or construct an opening in your wall, but check with your manufacturer before taking these steps.) So lets take a few minutes to look at what a masonry fireplace is (and what you might mistake for one).

What is a masonry fireplace?

Hover your cursor over the image below to find out.

Prefabricated Fireplaces

Some homes were built without masonry fireplace and later had fireplaces added to them. These are called prefabricated fireplaces. At first glance, both masonry and prefab look the same, but there are some pretty serious differences. A prefabricated fireplace is built after the home is built.  A factory makes these fireplaces then sends them to the house for installation.  Their parts are a metal firebox, metal or refractory panels, a metal chase cover, and a chimney cap.  The chimney pipe is made of metal, and the chimney itself is built from stucco or siding.

These fireplaces are built to contain occasional, decorative fires.  While masonry fireplaces are built to last as long as the houses they are built in, prefab fireplaces are not built this way.  They have shorter lifespans, which can be shortened further by burning many fires or by burning a fire large enough to warm the room.  Remember, they are designed to hold decorative fires.  Unfortunately, these fireplaces deteriorate over time, even if you don’t burn in them at all!

Why is this difference important to you? Prefab fireplaces rarely accept inserts, and if they do, they only accept certain models. It’s very important that you look to see what type of fireplace you have before purchasing an insert. Look at the chimney (is it made of brick or siding?) and the walls of your fireplace (are they stone or metal?).  This should give you a good idea of whether or not the fireplace in your home is masonry or prefab.

How does an insert work?

Fireplace inserts provide better safety and efficiency and fewer emissions than a traditional masonry fireplace. But how? It really comes down to the venting. When inserted into a masonry fireplace, inserts seal your chimney, keeping cold air out and forcing the hot air from the fire to flow into your home.

In the image to the right, you see how a fireplace insert seals your chimney.  Heat and fumes from the insert travel through the chimney liner and escape through the chimney cap.  A traditional masonry fireplace has no chimney liner, so there is essentially an open tunnel between the house and the outside.

If you put an insert into a wall or a frame, it will either be ventless or use direct venting. Both of these options seal the firebox off. No drafts. No escaping heat.

Do I need a fireplace insert?

Fireplace inserts aren’t necessary to have a fire. You can burn in your masonry fireplace; that is, after all, what it was designed for. However, masonry fireplaces are not efficient. If you want to add any significant amount of heat to your home with your fireplace, you’ll need an insert. If you want to reduce your emissions, you’ll need an insert. If you want greater safety, you’ll need an insert. Inserts aren’t necessary for decorative fires, but they are necessary for safe, efficient, heat producing fires.

Types of Inserts

Inserts are designed to burn specific fuel types. Gas, wood, and ethanol all burn at different rates and have different heat outputs. Because of this, you shouldn’t burn anything other than the specified fuel in your insert, unless specifically recommended by the manufacturer. Don’t burn coal in your wood insert. Don’t burn wood in your gas insert. Don’t pour gasoline in your ethanol insert. And most certainly don’t try to burn anything in your electric insert.

If you install a gas fireplace insert, you have two fuel options: propane and natural gas.  Essentially, they are the same: they produce the same amount of heat.  Most gas fireplace inserts are designed to run on one or the other, so you will need to decide which you want to use.  The key here is simplicity.  Do you have a natural gas line in your home?  Then use natural gas for your fireplace.  If not, consider having a propane tank installed.

One other difference is the ignition system.  Propane gas fireplaces come with a pilot light that will be used to start the fire.  Propane is heavier than air, so if you do not close the manual valve tightly, the propane will leak into the room and puddle inside the fireplace.  Because of this, propane systems always include a pilot light.  A small amount of propane is sent out of the tank so a small flame stays on all the time.  (If the propane hadn’t been closed properly and had puddled in your fireplace, and you then turned on the propane to light your fire, your match/lighter would create an explosion.  The pilot light will ignite any propane as it comes out so if you don’t close the propane tight enough, your fire will just keep on burning.) In contrast, natural gas is lighter than air and will escape through the venting if it is left on.

Some fireplace inserts come equipped with blowers.  (Other models don’t come with blowers but will accept certain blower models, but some inserts do not accept blowers at all.)  Blowers help increase the heat output on your fireplace.  They suck in air from the room; the fire warms this air; then the blower pushes the newly warmed air out into the room.  Ethanol fireplaces do not accept blowers, but wood, gas, and electric fireplaces all have models that can.

A variable speed blower requires a rheostat variable speed control, which allows the user to control the RPM speed of the blower’s motor.  This controls air flow (heat output) and the noise.  The higher the RPMs, the noisier the fan and the more heat is pushed out.  The control will either be at the base of the fireplace or mounted to the wall.  You can use a dimmer, if rated properly, to control the RPMs.

A thermostat limit switch is most commonly used in blower kit applications when no designated wall switch is present for the blower.  If there is a wall switch, this should be left at the ON position so the thermostat will take control of the blower.  Thermostat limit switches turn on the blower at 90 degrees and turn the blower off at 120 degrees.  These switches are held in place with magnetic brackets or small clips.

Most blowers contain three bearings.  Sleeve bearings are cheaper but wear faster and can turn noisily.  Ball bearings are more expensive, but they last longer and run quieter. Once you’ve chosen your fireplace insert, contact your manufacturer to see if it comes with a blower or what models of blower that insert will accept.

Ventless, Traditional, and Direct Venting

Fireplace inserts come with three main venting options.  The first is traditional venting, which has changed over time.  Originally, fireplace inserts did not connect to the chimney in any way to dangerous fumes weren’t forced to go up the chimney.  Later, a short length of stainless steel liner was installed up into the chimney.  This was called a direct connect, but direct connects have serious problems.  Creosote, ash, etc. doesn’t have to go up and out the chimney but can fall back down and accumulate on top of the insert.  Remember, creosote is flammable so this is not safe.

Now we have a much better option. When installing a fireplace insert, you should also install a stainless steel chimney liner that connects to your fireplace insert and goes all the way to the top of the chimney. At the top will be a chimney cap, and the bottom will be sealed to the insert.

Some fireplace inserts are ventless in nature (ethanol and electric) since no toxic fumes or smoke is produced.  However, new technology allows for gas fireplaces to be ventless as well.  While once controversial, vent-free technology has won wide acceptance.  Robert Dischner, a top manufacturer for fireplaces and grills, says, “The [ventless]  fireplaces use catalytic-converter technology (similar to exhaust systems on new cars sold in the U.S.), which cleans hot air as it leaves the combustion chamber.

Because of this technology, no chimney or venting is required.”  Modern ventless gas fireplaces are safe, and don’t necessarily need to be inserted into a masonry fireplace.  They can be installed in a frame or inserted into a wall since no venting is necessary.  (Note that there are no options for ventless wood-burning fireplaces.)

1. Combustion air is drawn from outside the building.
2. Cool room air is pulled into the lower chamber; it will circulate around the firebox and is released into the room as warm air via the fan. The heat from the central burner also emits more radiant heat from the face of the unit, into your living space.
3. The terminal is mounted outside, connecting to the fireplace indoors.
4. Venting exits from the top or rear of the fireplace to allow more versatility for installation.
5. Optional rear exhaust
6. Direct vent power venting can be installed to go around stairways, up, down and around most objects in any space.

The below to the right is a wood burning insert with direct venting. You can tell that it uses direct venting since the insert has not been installed into a pre-existing masonry fireplace, which would use traditional venting.

Fireplace Inserts vs. Stove Inserts

As you look for fireplace inserts, you might also see stove inserts being sold. Let’s take a look at the difference, starting with the definition of a wood stove. A wood stove is a freestanding firebox.  Oftentimes, the top of the firebox will be a flat surface like a stovetop.  Wood stoves hold wood fires, and as your fire heats up, it will heat this flat surface and you can cook foods in pots and pans, just like you would on your stove.  Wood stoves are designed to produce enough heat to warm entire homes.  They are extraordinarily heat efficient.

A wood stove insert is a modified wood stove, designed to fit into a masonry fireplace and vent through a pre-existing chimney.  Like the traditional wood stoves, they are designed to be extremely heat efficient.  A good wood stove insert will heat your entire home.  Unfortunately, the inserts do not come with cooktop space, though you can still bake items in the hot embers. The essential difference between fireplace inserts and stove inserts is heat output, at least when it comes to the wood burning stoves. You can also buy electric stove inserts and gas stove inserts, but these will really only differ in design from the electric and gas fireplace inserts.

You may also see pellet stove inserts being sold. Pellet stoves are very similar to wood burning stoves.  They are freestanding units composed of a firebox, a hopper, and venting.  Instead of “tending” a fire like you do with a traditional wood stove, you simply keep the hopper full of pellets and the fire feeds itself.  Pellets are small pieces of heavily compressed, recycled materials.  They produce far less ash than wood, so there is less clean up, and require less maintenance: just keep the hopper full, and the fire will keep burning.

Burning pellets has certain advantages:  Pellets produce less creosote than firewood.  (Creosote is a flammable byproduct of combustion.  It can build up and cause chimney fires.)  Less creosote means less cleaning of the venting system.  Pellets, being compressed, have less moisture than firewood, and, thus, burn hotter and cleaner.  Plus, wood pellet stoves produce fewer pollutants than traditional wood fireplaces.

Just like the wood stove insert, the pellet stove insert is a modified version of a pellet stove.  It is designed to fit neatly into a pre-existing masonry fireplace and vent through a pre-existing chimney.  Pellet stove inserts can come with decorative pieces like ceramic logs or rocks.

Whether you choose an simple electric insert or a wood stove insert with a blower and direct venting, your new insert will be safe and efficient. It will have low or no emissions, and it will be the focal point in your home for years to come. If you have other questions leave a comment below.