How to choose a fireplace insert: a practical, jargon-free guide
Everything you need to consider before buying an insert: output, fuel type, opening dimensions, installation and regulations. No technical jargon.
Before buying an insert, measure the opening of your existing fireplace and assess the condition of the flue. An incorrectly sized insert or one installed in a damaged flue can be dangerous. Always request a prior inspection.
Installing an insert in an open fireplace is one of the best investments you can make to improve home heating. You can go from an open fireplace with 10–15% efficiency to an insert that makes use of 70–80% of the heat from the firewood.
But you need to choose carefully. The market is full of options and catalogues can be confusing. Here we explain the points that really matter.
1. Measure the opening before looking at models
The first step is to measure your fireplace opening: height, width and depth. The insert must fit without leaving excessive gaps at the sides. Most manufacturers provide the opening dimensions and required depth.
Also measure the diameter of the existing flue. Many inserts require 150 or 200 mm flues, and if yours is different it will need to be adapted with a flexible corrugated liner or similar.
2. Wood or pellets: fuel type matters
Wood-burning inserts: these are the most common. Easy to use, they do not depend on electricity (except for the heat-distribution fan). Efficiency ranges from 60% to 85%. They require manual refuelling.
Pellet inserts: automatic feeding, thermostat control and greater convenience. However, they depend on electricity and pellet prices vary. Efficiency ranges from 80–92%. Ideal if convenience is your priority.
Biomass or combined-fuel inserts: less common and more expensive. Intended for specific situations.
3. Output: neither too high nor too low
An output that is too high for the room means you are always running it at the lowest setting, which reduces efficiency and creates more creosote deposits. Too low, and it will not heat sufficiently.
As a general guide: for a well-insulated 30–40 m² living room on the Catalan coast, 6–8 kW is sufficient. For inland areas or the Pyrenees, or homes with greater heat loss, 8–12 kW or more may be needed.
4. The flue is the most important part
A new insert installed in an old, cracked flue or one with poor draught will not work properly. Before installation, the flue must be inspected and in good condition.
If the flue is old or cracked, it may be necessary to line the inside with a stainless-steel or flexible corrugated liner. This cost needs to be included in the overall budget.
5. Installation: always use a professional
Installing an insert requires adaptations to the flue, sealing work and, in some cases, municipal permits. It is not a DIY job. Poor installation can cause carbon monoxide poisoning or a flue fire.
We do not install inserts, but we do carry out the preliminary flue inspection and can tell you what condition it is in and what it needs before installation.
6. Maintenance after installation
An insert requires more maintenance than an open fireplace, although it is also more efficient. Wood-burning inserts need the flue cleaned at least once a year. With pellet inserts, the flue and burner need more frequent cleaning.
How much does it cost to install a fireplace insert?
The unit can cost between €1,000 and €4,000 depending on the brand and model. Installation adds another €300–€800, and if the flue needs lining, this can add a further €400–€1,000. As a rough guide, the total is between €1,500 and €5,000.
What happens if I install an insert without inspecting the flue?
There is a risk of carbon monoxide poisoning from smoke leaks or a flue fire if creosote has built up or cracks are present. The preliminary inspection is not optional; it is a safety requirement.
How often should the flue be cleaned with an insert?
With wood, at least once a year. With pellets, the flue accumulates less soot, but the burner and collector require more frequent cleaning. Follow the manufacturer’s instructions.
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