What Kind of Flue Do You Need for an Oil Appliance?

Installing or replacing an oil appliance like a boiler or cooker in your home requires careful consideration of the flue. An oil boiler flue is the pipe that connects the appliance to the chimney and safely removes exhaust gases. Choosing the correct type of oil boiler flue pipe is essential for safety, efficiency and compliance with building regulations. This article will explain the different types of flues available and the factors to consider when selecting one. 

Why Do You Need an Oil Boiler Flue? 

An oil boiler flue has two key jobs: 

1. To transfer exhaust gases safely from the appliance to the outside of the building. Oil appliances produce carbon monoxide, which can be deadly if allowed to accumulate indoors. 

2. To provide sufficient draw to ensure complete combustion. Correct draw pulls air into the appliance to properly burn the oil fuel. Flue pipes and liners contain and channel hot gases upwards via the chimney's flue passage. They prevent leakage into surrounding masonry, which could start a fire. Liners also insulate the flue, helping maintain hot gases for adequate draw. 

What Are the Flue Options for Oil Appliances? 

There are a few main choices when selecting an oil boiler flue: 

Balanced Flue 

Balanced flue liners allow both air intake and exhaust through concentric ducting. They can be used where a chimney is unavailable. The inlet duct provides combustion air directly to the appliance. Balanced flues avoid drawing air from within the building. 

Stainless Steel Flexible Liner 

Flexible stainless-steel liners are designed for re-lining existing chimneys. They are corrugated for flexibility to insert into the flue passage. The liners are comprised of alloy coated with aluminium and silicone. Stainless steel flex liners are an ideal solution when replacing an old appliance without re-building the chimney. 

Double Skin Stainless Steel 

Double-skin stainless steel flue liners have an air gap between an inner and outer steel layer. The air insulation improves flue draft and gas temperatures. These liners suit high-efficiency condensing boilers. The interlocking design allows easy installation. 

Key Factors to Consider When Choosing a Flue 

There are several important factors to consider when selecting the correct type of flue liner: 

Flue Diameter 

The flue pipe diameter must suit the size of the appliance's flue outlet. A liner too small in diameter will restrict gas flow. Manufacturers provide minimum size guidelines based on appliance heat output. An oil boiler flue too large in diameter will also impact the proper draught. 

High-Efficiency Condensing Boilers 

New high-efficiency oil boilers are condensing types, which require specialised flues. The oil boiler flue pipe must withstand acidic condensate without corrosion. Stainless steel grades 316Ti or 904L are ideal materials for condensing boilers. 

Manufacturer Instructions 

Always check the appliance manufacturer's instructions for any flue requirements. The oil boiler flue must be suitable for the specific appliance model and fuel type. The flue diameter and material should meet the manufacturer's specifications for safe operation. 

Sealing and Gaskets 

The flue liner connections must be adequately sealed. High-temperature silicone gaskets are used to seal liner sections. The gaskets prevent leakage of gases and maintain optimal flue draught. Proper assembly is essential following manufacturer guidance. 

Certification and Standards 

Choose a certified oil boiler flue pipe or liner conforming to standards like CE marking or national standards such as BS EN 1856-1. This ensures the flue or liner is constructed from quality materials and designed for safe use with oil-fired appliances. 

Access for Cleaning and Servicing 

Flue pipes should include access points to allow for cleaning and inspection. Condensate drains and cleaning hatches enable maintenance for safety. They should be removable or have connections, allowing access to clean soot and debris as needed. 

Installation Considerations 

Proper installation of the flue liner is critical. Here are some essential installation factors: 

• A continuous upward slope allows condensate drainage for high-efficiency boilers.
• Rigid stainless steel flue sections are connected and sealed according to manufacturer specifications.
• Flexible liners should be supported and secured to maintain an open flue passage.
• Flues must be insulated from combustible materials like wood framing.
• Terminate the flue according to building regulations for height and location.
• Specialist installation by a Gas Safe registered engineer is recommended.

Maintenance and Inspection 

Once installed, the flue liner should be regularly maintained and inspected. An annual service check is recommended. Look out for: 

• Blockages: Check for build-up of soot, debris or vegetation that could cause back-ups. Clean out as needed.
• Corrosion: Look for signs of rust and corrosion, particularly with metal flues. Stainless steel is more corrosion resistant. 
• Leaks: Inspect joints and seals for any gases or fumes leaking into the property. Reseal joints as required. 
• Damage: Check the flues exterior for damage by weather or animals. Repair or replace damaged sections. 
• Testing: Flue gas analysis can check for proper drafting and combustion. 

When to Replace a Flue 

If an old flue liner shows significant deterioration, a replacement will be needed: 

• Holes, cracks, blockages or severe corrosion. 
• Joints have failed, allowing fume leakage. 
• The flue is no longer adequately heat-resistant. 
• Safety cannot be verified even after maintenance. 
• The old flue is unsuitable for a new high-efficiency boiler. Replacing the flue provides an opportunity to upgrade to a higher-specification model. 

Additional Considerations 

Here are some extra factors to consider when selecting and installing a flue: 

Existing Flue Condition 

The condition of the existing chimney and flue passage must be assessed. Damage, blockages or excessive offsets can prevent the proper installation of a new liner. Chimney repairs may be needed beforehand. 

Approved Flue Routes 

There are strict rules governing flue routes from the appliance to the termination point. Flues should take the most direct way and avoid too many direction changes. 

Listed Components 

Ensure all parts like connectors, terminals and clamps are certified as compatible components of the flue system. Mixing parts can compromise safety. 

Local Regulations 

Building regulations and codes often specify requirements for oil flues and installation. Check rules to ensure compliance. A safety inspection may be required. 

Weather Protection 

The flue outlet should have a weatherproof terminal to prevent rainwater ingress. A cowl can help prevent downdraughts. Lightning protection may be needed for exposed chimneys. 

With careful planning and professional installation, a high-quality flue liner matched to the appliance will provide safe and reliable service for many years. The liner choice, condition, and maintenance help minimise the risks of open-flued oil fuel systems. Browse oil flue options here.