Do I Need a Chimney Liner for My Gas Boiler? Venting Code Requirements in 2025

If you’re installing a boiler like the Weil-McLain CGA-4 Series 3, one critical but often overlooked detail is your chimney liner. Mike Sanders—a smart, safety-conscious homeowner—knows that skipping this can cost you big in efficiency, compliance, or even safety. So, do you need a liner in 2025?

Let’s break down when liners are required, how they work, what they cost, and how they impact the performance of gas boilers like the CGA-4.

🔥 1. What Is a Chimney Liner and Why Does It Matter?

A chimney liner is a protective layer inside your chimney that helps safely vent combustion gases from your boiler. It improves:

• Heat transfer: Keeps exhaust warm enough to rise safely

• Draft performance: Ensures flue gases flow properly

• Condensation control: Prevents moisture buildup from acidic flue gas

• Fire protection: Isolates heat and flames from surrounding masonry

➡️ Without a liner, carbon monoxide or moisture can leak into your home or chimney structure.

CSIA Chimney Safety Facts

🧱 2. When a Chimney Liner Is Required (2025 Code Updates)

According to IRC (International Residential Code) and NFPA 211, liners are required when:

• Converting from oil or coal to gas

• Installing a new boiler into an unlined masonry chimney

• Downsizing BTU output without resizing the flue

• Installing a high-efficiency appliance (if not direct vented)

📌 For the Weil-McLain CGA-4:

• It’s a Category I appliance (non-condensing, atmospheric vent)

• If venting into a masonry chimney, you need a properly sized liner to prevent draft failure and flue gas cooling

IRC Code Reference – Section M1801

🛠️ 3. Types of Chimney Liners

Type	Material	Cost (Installed)	Lifespan	Pros	Cons
Clay tile	Terracotta	$1,500–$3,000	30–50 years	Traditional, durable	Not ideal for gas appliances
Stainless steel	Flexible/rigid	$900–$2,500	15–30 years	Ideal for gas, easy retrofit	Can degrade in acidic exhaust
Aluminum	Lightweight	$600–$1,200	10–15 years	Budget-friendly	Not code-compliant in all areas

➡️ Mike’s choice: Stainless steel liner is the best match for a CGA-4 installation in a masonry chimney.

📋 4. What Happens If You Skip the Liner?

• ❌ Code violations — May fail inspection or invalidate permits

• ❌ Backdrafting — Combustion gases spill back into the home

• ❌ Moisture and flue erosion — Condensate soaks brick, breaks mortar

• ❌ Reduced efficiency — Flue gases cool and stall in oversized chimneys

• ❌ Warranty issues — Manufacturer may void coverage without liner

➡️ Installing a liner is not just a formality—it’s required for safety and performance.

💸 5. Chimney Liner Costs in 2025

Component	Typical Range
Stainless steel liner kit	$300–$800
Pro installation	$700–$1,700
Total project cost	$1,000–$2,500
Inspection/permits	$100–$350

Regional Variance:

• Higher in the Northeast or historic homes

• Lower in Midwest or during full HVAC installs

➡️ Mike’s budget tip: bundle liner install with your boiler quote—HVAC pros often discount it.

🧰 6. How to Know If You Already Have a Liner

DIY Checks (Visual):

• Look for a metal pipe or flue inside chimney throat

• Remove cap from chimney top and inspect with flashlight

Professional Confirmation:

• HVAC technician or chimney sweep uses camera inspection

• Inspection cost: $150–$300

➡️ Don’t assume—many older homes have unlined or cracked flues.

📐 7. Sizing the Liner for a Weil-McLain CGA-4

• The CGA-4 produces 100,000 BTU/hr

• Minimum flue size: typically 5”–6” round stainless steel liner

• Must match vent connector size per ANSI Z223.1 (National Fuel Gas Code)

Weil-McLain CGA-4 IOM Manual

➡️ Oversized liners cause draft failure. Undersized = backpressure.

🧠 8. Mike’s Final Checklist

1. Installing into masonry chimney? ✅ Get a stainless liner

2. Doing a fuel conversion? ✅ Code requires a liner

3. Flue size mismatch? ✅ Liner corrects draft path

4. Liner already there? ✅ Verify it's intact and gas-rated

5. Venting into B-vent or direct vent? ❌ Liner not required

✅ Conclusion: Do You Need a Liner?

Yes—if you’re venting a Weil-McLain CGA-4 into a masonry chimney, a properly sized stainless steel chimney liner is required in 2025.

It ensures:

• Code compliance

• Safe flue gas removal

• Full boiler efficiency

• Longer chimney life

For Mike Sanders and other savvy homeowners, this is a smart upgrade that protects both your family and your investment.

In the next topic we will know more about: Will a Weil-McLain CGA-4 Fit in My Utility Room? Clearance, Noise & Venting Considerations