Ever had the thought that some people are just fancy Nancy's when they talk about the new fireplace they got installed? Everything from closed combustion to heat output and efficiency, but you have no idea what it means? We’re here to give you the low down on everything you need to know about a closed combustion fireplace; What it is, how it works and why it is so efficient.

What is a closed combustion fireplace?

A closed combustion fireplace refers to a fireplace that literally closes with a door. The chamber that you make the fire in, is sealed shut with a door and draws oxygen from the outside through vents in the fireplace. Closed combustion fireplaces are some of the most efficient fireplaces on the market. It burns less wood, creates more heat, and is safer because the fire is behind a closed door; with no stray sparks flying around.

How does a closed combustion fireplace work?

Once the fire is lit, the primary and secondary air vents create an opposite flow of air inside the fireplace. On the diagram below, the dark blue arrows indicate the flow of air from the primary air vent – letting air in at the bottom of the fireplace that will rise to the top as the oxygen fuels the fire. The secondary air vent, shown by the light blue arrows draws oxygen in from the top of the fireplace, in an opposite direction. Proper use of the air vents will ensure that the wood burns at a slower rate.

How does a closed combustion fireplace work?

The hot smoke will evaporate through the flue pipe, radiating about 50% of the heat that the fireplace can produce. Our cast iron fireplaces are a good example of a closed combustion fireplace. Cast iron heats very slowly because of its low heat conductivity but retains heat extremely well once it reaches a high temperature. Meaning that once your fireplace is hot, it will radiate heat long after the fire has died.

Bosca Closed Combustion Fireplaces

What makes a Bosca fireplace different from a regular cast iron fireplace?

Besides the look that is more modern, our Bosca fireplaces work with a double combustion system. A double combustion system is exactly what the name says, it will combust twice. The fireplace has two chambers within the main firebox. At the bottom is the first chamber, which we can see through the glass door, where you will make your fire. As indicated with the first combustion bracket on the diagram below. The second chamber is concealed within the fireplace with an angled metal plate preventing the hot smoke from directly escaping through the chimney.

The smoke is forced to pass through the second chamber where more cold air is drawn in through a vent at the back of the fireplace. It combusts again, creating more heat before it escapes through the flue pipe. The double combustion system is also more eco-friendly than any other fireplace because most of the waste from the first combustion gets reduced once it passes through the second chamber.

What makes a Bosca fireplace different from a regular cast iron fireplace?

Efficiency and craft of a Bosca Closed Combustion Fireplace

Space for wood
The fireplace was designed with a small gap between the sides of the fireplace and the main chamber that runs all the way around the fireplace to the bottom wood storage. The heat that generates in the chamber radiates and creates a convection in this gap. Wood that is stored in the space here will dry and preheat as the fire is burning, to ignite quickly once you add it to the fire.

Universal Bosca Key
All Boscas were designed with a universal tool to open the fireplace door, and ashtray. The key-like tool detaches from the door when in use, so that when you want to open the door, the handle won’t burn you.

Bosca key

Power interior
All Boscas are fitted with fire bricks inside the main chamber made from vermiculite. The purpose is to insulate the main chamber so most of the heat radiates through the glass and the chimney. The fire bricks will also protect the inside of your fireplace from the intense heat created by the fire, increasing the longevity of your fireplace.

Ignition system

Each Bosca fireplace has an easy-to-ignite system installed, that can be adjusted with the universal tool. To ignite your fire, open all the vents towards the ‘E’ as illustrated in the picture below. This opens all the vents for maximum oxygen to ignite your fire. Once lit, adjust the vent for less air intake towards the ‘-‘and more air intake towards the ‘+’.

Ignition system

A fireplace isn’t complete without a flue pipe

A flue pipe is an integral part of the success of a fireplace. Not only is it the exit of the smoke from the fire, but it radiates about 50% of the heat generated within the main chamber. Our Megamaster Stainless Steel Installation Kits were specifically designed to keep water out and smoke in.

Installation Kit

Top tips for any closed combustion fireplace

  • Avoid big yellow flames. Always aim for a lazy flame with hues of blue and red. Because of the efficiency of the design of the fireplace, it’s not necessary to make a massive fire for optimal heat output.
  • Always clean your fireplace after winter and burn it in again before the cold sets in again.
  • Maintain your fireplace by taking care of leaks, rust, and black stains on the glass.
  • Experiment with the air vents by closing the secondary air vent and just using the primary air vent. The wider you open it, the more oxygen it will draw in.
  • The moment you see the flame is dying, open the second air vent to draw more oxygen in.

Check out our frequently asked questions section for more information. If you’re ready to shop, have a look at our range today.

Closed combustion fireplace