An open masonry fireplace typically converts less than 20% of the wood's energy into room heat. The rest disappears up the chimney, taking warm indoor air with it. Modern closed-combustion units routinely achieve 75–85% efficiency — a fourfold improvement using roughly one-third of the wood.
The efficiency gap in real numbers
For a 60 m² lounge, an open fireplace burns roughly 4 kg of wood per hour to produce a comfortable ambient temperature. A closed-combustion unit rated at 8 kW delivers the same comfort on 1.2–1.5 kg per hour. Over an average Cape winter that is the difference between two bakkie-loads of wood and half a load.
Indoor air quality
Open fireplaces draw combustion air directly from the room, pulling cold air in through every gap in the building envelope. Closed units — especially those with an external air kit — take combustion air from outside, so warm indoor air stays inside. This is particularly relevant in modern airtight builds where an open fire can create dangerous back-draught conditions.
When an open fireplace still makes sense
- Heritage restorations where the original hearth is a listed feature.
- Occasional-use holiday homes where ambience matters more than heat.
- Homes with an existing masonry firebox that a closed-combustion insert can be retrofitted into (the best of both worlds).
Retrofitting a closed insert
If you already have a masonry chimney, a cassette-style closed insert slots into the opening and connects to a new flexible liner. Installation typically takes a day and immediately delivers the efficiency gains above.
What switching costs
Replacing an open fireplace with a freestanding closed-combustion unit is a one-day job for most single-storey homes. At our prices (incl. VAT) the pieces are:
- Installation: R 5 500 single-storey or R 8 000 double-storey, including one core drill.
- Top-exit connection into an existing chimney: from R 1 830.
- Or a new stainless flue through the roof: R 6 715 (Ø130 mm, up to 10 kW), R 7 390 (Ø150 mm, 11–15 kW), R 8 505 (Ø180 mm, 16–18 kW).
- Double-storey flue add-on: R 3 000.
- Transport: R 500 for the first 20 km, then R 10 per km.
A local example
A typical Durbanville or Bellville family room of about 40–60 m² is well served by a 10 kW fireplace. This month's Magma special is R 16 500, or R 23 970 fully installed with the flue kit in a single-storey home. With wood use falling by around two-thirds compared with an open hearth, the saving on firewood alone is noticeable from the first winter.
Which suits your area
- West Coast (Table View, Melkbosstrand, Langebaan): closed units cope far better with the wind, which causes smoke blow-back in open fireplaces.
- Winelands (Stellenbosch, Paarl, Franschhoek): cold, still nights reward long overnight burns only a closed unit can manage.
- Southern suburbs heritage homes: a closed insert keeps the original surround while fixing the heat loss.
Next step
Send us a photo of your current fireplace and the room size. We'll tell you whether your chimney can be reused and give you an installed price the same day.
Quick answers
Can I keep my existing chimney? Often, yes. If the masonry is sound, a top-exit connection from R 1 830 links a closed unit into it, saving the cost of a new flue through the roof.
Will a closed fireplace still give me a view of the flames? Yes. Modern units have large ceramic glass doors with an air-wash system that keeps the glass clear, so you get the flame picture without the heat loss.
What size do I need? Roughly 1 kW for every 8–10 m² of well-insulated room. Our sizing guide and flue advisor help you pick the right unit and flue.
Written by
Progress Group
Fireplace, braai and gas specialists since 1990 — showroom in Bellville, installations across Cape Town and the Western Cape.