A chimney and fireplace with stone surround. The fire is lit and there are animal decorations on the hearth.

I have fond memories of sitting in front of the fireplace in my grandparents’ front room as a kid. Their home had several chimneys and fireplaces, which I thought was amazingly cool.

Watching the flames flicker and the wood sizzle and pop was mesmerizing.

No matter what was on my mind or what troubles my 10-year-old self was worried about, a cup of cocoa and a seat in front of the fire would relax me and calm my problems away.

I even enjoyed chopping wood for the fire with Gramps. He had a wooded area on his property which we would harvest from, and I learned to use an ax under his tutelage. It was a bonding experience that I’ll always remember.

a living room with the fireplace going and two people's feet propped up on the coffee table, showing they are relaxing

Fast forward to the present day, and I want to recreate the magic of an open fire in my new home so my kids can experience the same thing I did as a child.

The only problem is that modern construction techniques make it difficult to install an open fire without compromising on other design goals.

You see, modern homes are far more airtight than houses decades ago, creating issues with open fires.

For an open fire to work properly, it needs a supply of air that can be used in combustion and to create a draft that carries the products of combustion away up the chimney to be discharged into the atmosphere.

If you light an open fire in a modern, airtight home without opening a window to let air in, you can have smoke blowing back into the room instead of being carried away up the chimney.

I’ve seen this happen in a friend’s home and don’t want the same problem in my own house.

I built my home using the latest modern construction techniques, and it is pretty airtight.

It seems a shame to install an open fireplace that will draw air in from the room and send it straight out through the chimney. Even worse, I would need to open a window whenever I light the fire to avoid smoke blowing back into the room.

So, I’ve investigated the options available for having an energy-efficient home while also enjoying the experience of a fireplace in my living room, and this is what I’ll share with you in this article.

Open chimneys and fireplaces are inefficient because they draw cold air into the home from outside and allow hot air to escape up the chimney. Sealing your chimney with a cap, draft stopper, or closing the damper when the fireplace is not in use, will improve your fireplace’s energy efficiency.

In my research for installing a fireplace, I came across different solutions for improving the energy efficiency of existing fireplaces, alternative fireplace designs, and the best ways of sealing up a disused fireplace and chimney.

I lay it all out for you to read in the rest of this article, so read on to learn more about this topic.

The Anatomy of a Fireplace

Before we get into the different options available to you, let’s remind ourselves about the rudiments of chimney design and how the different parts of a fireplace do their job.

You’ll find variations in design across the country and even between houses on the same street, but there are common design characteristics that most chimneys and fireplaces share.

Let’s look at some of the main ones.

Hearth

A stone hearth with a lit fire and a Christmas tree on the left hands side. There is a clock on top of the mantelpiece.
A hearth makes the perfect landing pad for Santa Claus as well as forming a centerpiece for the living room.

The hearth is the structure that extends out into the room at floor level from your fireplace and comprises the inner hearth, which is inside the opening, and the outer hearth, which extends beyond the firebox into the room.

Its purpose is to protect the floor from sparks or logs that fall out of the fire, although a pleasant hearth also serves a decorative purpose because it draws the eye to the fireplace and can have an attractive look.

Hearths usually are made from concrete, stone, or tile. My grandfather had a beautiful slate hearth in his front room, which I always thought looked very elegant, especially after it had been cleaned.

Mantel

A mantelpiece above a fireplace with a clock and candles resting on it.
Originally serving the practical purpose of preventing smoke entering the room by funneling it up the chimney, these days the mantel is more often used to display ornaments.

The mantel originally served the purpose of catching smoke and channeling it up the chimney. However, these days they are mainly for decorative purposes, with some being very ornate and extending a long way from the fire itself.

The mantel is the most prominent part of the fireplace surround, and you’ll often find the shelf used to display ornaments.

Firebox

This is where the action happens. Sometimes referred to as the firepit, the firebox is the space where the fire is built and is usually situated at floor level in the room.

The firebox is constructed with special bricks and mortar that are resistant to the intense heat that the fire will generate.

Fire bricks (refractory bricks) are used around the firebox and contain ingredients such as alumina or silicon that boost their resistance to heat.

They must be tightly arranged in a thick enough formation to protect the rest of the house from the heat of the fire.

The mortar used in the firebox must also be refractory to ensure that the fire bricks hold together and don’t fall off when the fire is lit.

The type of refractory mortar must match the fire bricks used. So, silica refractory mortar is used with silicon fire bricks, and high alumina bricks require high alumina refractory mortar.

Damper

The damper is a door or valve fitted in the flue’s opening.

The damper is used to control the draft of the fireplace. When the fireplace is not in use, the damper should be closed completely to prevent warm air from escaping the home via the chimney.

Likewise, the damper must be opened before lighting a fire. Otherwise, the flue won’t draft properly, and smoke will blow back into the room from the fire.

Smoke Chamber

Chimney sweep with a brush covered in creosote, smiling at the top of the flue.
Regular sweeping of the chimney helps to keep it functioning efficiently by avoiding the build up of creosote and soot.

The smoke chamber is the funnel-shaped space immediately above the firebox that directs the smoke into the flue and up the chimney.

It’s essential to keep the walls of the smoke chamber clear of soot and creosote with regular sweeping.

A build-up of creosote is particularly important to avoid. It forms from cooled smoke that sticks to the walls of the smoke chamber as the tar and other substances in the smoke condense onto the walls of the smoke chamber and flue.

Creosote is flammable and is the cause of many chimney fires. The excessive build-up of creosote also obstructs the chimney and can cause smoke and poisonous gases such as carbon monoxide to back up and enter the home.

Flue

A chimney sweep cleaning the flue with a brush from the roof.
The flue needs regular sweeping to keep it functioning well.

The flue is the vertical channel that allows the smoke and combustion gases to leave the firebox safely and vent into the atmosphere.

As the hot air rises from the firebox, it travels up the flue, creating a draft. The stack effect causes this draft, the phenomenon of warm air rising within the structure, drawing in cold air from outside as it does so.

Despite the assumption that many of us have that the flue is wide enough for a fully-grown, well-fed man to climb down into the fireplace from the roof, that’s actually not the case.

Santa Claus uses magic to fit down the chimney; the rest of us can’t fit in this narrow space.

Chimney Cap

Two chimneys on top of a roof with pitched chimney caps.
Chimney caps stop rain falling down the inside of the chimney and keep vermin out.

Placed over the very top of the chimney, the chimney cap prevents vermin from entering the chimney.

It also stops rain from entering the chimney but is designed in such a way as to allow the smoke and combustion gases from the fireplace to vent to the outside safely.

Ash Pit

The ash pit is located beneath the firebox and is a cavity into which the ashes from the fire fall.

The ashes can be cleaned out via a door at the bottom of the chimney or by lifting out an ash box in the ash pit.

Energy Efficiency of Different Types of Fireplaces

If you’re looking to maximize the efficiency of your home’s energy usage, you’ll want to ensure your house has top-notch insulation and is super airtight.

If that’s what you’re going for, you don’t have that many options for installing a fireplace.

Low air exchange rates don’t work very well with open fireplaces because air needs to be drawn into the room to allow for a draft up the chimney, which is essential for the flue to operate effectively and let all the smoke be taken outside.

In a modern, well-air-sealed home, a traditional fireplace doesn’t really fit in.

There are basically two types of fireplaces.

B-vent (Less Efficient)

An open (B-vent) fireplace with red brick surround in a room with a wooden floor that has a red patterned rug and green armchair.
Open B-vent fireplaces are less efficient than direct vent fireplaces because they draw in cold air from outside and allow warm air from the room to escape up the chimney.

B-vent fireplaces are open to the room and draw air into the fireplace from the room itself. They are what most of us think of when picturing a traditional fireplace.

The flue pipe of a B-vent fireplace consists of a single pipe that handles the exhaust from the fireplace.

The B-vent design must always terminate vertically, so it can never terminate through a sidewall.

Thanks to their open design, B-vent fireplaces have access to a lot of oxygen and can give rise to beautiful visible flames.

However, B-vent fireplaces are not as efficient as direct vent units because they constantly draw in cold air from outside. Also, they allow a lot of heat to escape up the chimney compared to direct vent systems because they are open.

They have an excellent visual appeal, and if you enjoy tending your fire in the evening, you might prefer to forego the better efficiency of a direct vent unit in favor of the more open B-vent design.

Direct Vent (More Efficient)

A direct vent fireplace behind a glass door in a white wall.
Direct vent fireplaces are more efficient than B-vent fireplaces because they don’t draw in cold air from outside and prevent warm air from the room escaping up the chimney.

Direct vent fireplaces are sealed units with no air exchange between the fireplace and the room.

They have a double-walled, coaxial flue, which draws outside air into the fireplace for combustion down the annulus of the outer pipe.

The inner pipe handles the exhaust gases and smoke, which are sent up the flue and vent into the atmosphere.

A direct vent fireplace can have its flue going sideways through a wall or vertically through a roof.

Direct vent units are sealed from the air in the room, so they don’t pull cold air into the room from outside and can build up more heat than B-vent units, which makes them more effective and efficient.

Increasing the Energy Efficiency of Chimneys and Fireplaces

As described above, if you have a direct vent fireplace installed in your home, it will be more energy efficient than a traditional, open B-vent fireplace because it is a sealed unit.

However, if you have a traditional B-vent fireplace, there are things that you can do to improve its energy efficiency.

Let’s look at a few now.

Chimney Insulation

If the walls of your chimney are too cold, this can encourage the condensation of combustion products onto them.

This condensation process results in the build-up of creosote on the flue walls, which can obstruct the flow of exhaust gases and smoke up the flue.

This reduces the fireplace’s efficiency by slowing the exchange of air and reducing the amount of oxygen available for combustion.

Creosote is also flammable, so this build-up presents a fire risk. Not to mention the health risks associated with an obstructed flue that causes smoke and toxic gas to enter the room instead of passing out through the chimney.

Fitting a chimney liner with proper insulation can help to fix this problem. Code requirements vary but typically require a stainless-steel chimney liner to be insulated with a half inch of a product like ProFoil.

Wrap the insulation around the chimney liner before you install it, hold the chimney insulation in place with foil tape and wrap the whole pipe in mesh to keep it secure.

Doing this will improve your existing chimney’s efficiency and prevent the harmful build-up of creosote in the chimney liner, keeping it free from obstructions and operating efficiently.

The other benefit of this type of chimney insulation is that it will keep the flue warmer, improving its ability to draft compared to if it was colder. This enhances the energy efficiency of the fireplace.

Chimney Caps

Chimney caps can be fitted to the top of the flue to act as an air seal while the chimney is not in use.

They come in different designs and can be installed on disused chimneys to provide a permanent seal that will stop drafts and heat from escaping from the home via the chimney.

Chimney caps also prevent rain and vermin from entering the home via the chimney.

There are even chimney caps available that can be operated from inside the home to be opened when the fireplace is in use and closed when it is not in use.

For more information about air sealing your home, please take a look at our article on the subject here.

Close the Damper

A chimney sweep looking up the chimney with a flashlight and brush, possibly ensuring the damper is closed.
The damper is usually located just above the firebox and should be closed when the fireplace is not in use to prevent drafts. Remember to reopen it before lighting the fire though.

As described above, the damper is the plate that closes off the flue from the firebox. The damper should be closed off when the fireplace is not in use to prevent warm air from inside the home, leaving the house up the chimney.

Don’t forget to open the damper back up before lighting the fire, though. Failure to do so will prevent the combustion products and smoke from venting properly to the outside.

Fireplace Draft Stopper

A fireplace draft stopper is a product that can be fitted to a chimney during extended periods when it is not being used.

It is an inflatable sack made from polyurethane that effectively blocks the hole in your house created by your chimney.

Once fitted, it will prevent the escape of warm air up your chimney, lowering your heating costs if you choose not to use the fireplace.

It comes with a supporting T-piece that helps to keep the draft stopper in position and also serves as a reminder of its presence, so you remember to remove it before lighting the fire.

Summary

Fireplaces have a long history, dating back to 12th century Europe.

However, the design of open B-vent fireplaces leaves much to be desired regarding energy efficiency.

In these modern times of well-air-sealed homes, open B-vent fireplaces waste a lot of energy compared to more advanced heating systems.

Direct vent fireplaces are a much more efficient alternative because they are sealed units that don’t lose heat up the chimney to the same extent and don’t cause cold air to be drawn into the room from outside.

If you have an open B-vent fireplace, there are measures you can put in place to improve the efficiency of your fire. These include the following.

  • Fit a chimney liner and chimney insulation. This improves the flow of combustion products and prevents the build-up of creosote on the inside of the flue.
  • Fit a chimney cap to the top of your chimney. These are available as permanent closures or with mechanisms that allow you to open and close the cap as needed.
  • Always close your chimney’s damper when the fire is not in use (but remember to open it again before using the fireplace).
  • Fit a fireplace draft stopper if not using your fireplace for a prolonged period. This prevents drafts and the loss of warm air up the chimney.

For more information about improving the energy efficiency of your home, why not read our article on 17 Energy Efficiency-Improving High ROI Home Upgrades?

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