Gas Line Requirements for a 133,000 BTU Boiler:
Mike’s Rules So You Don’t Starve the System**
If Your Boiler Isn’t Getting Enough Gas, It Will Burn Money, Not Heat Your Home.
Let me start with the most painful truth in hydronic heating:
**99% of boiler performance issues aren’t boiler issues.
They’re GAS SUPPLY issues.**
I don’t care if you bought the best boiler on Earth —
if the gas line feeding your Weil-McLain CGA-5 is undersized, undersupplied, or incorrectly routed, your system will NEVER reach full output.
Undersized gas piping =
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delayed ignition
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weak flame
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poor combustion
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soot buildup
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high CO output
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flue condensation
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short cycling
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burner rumble
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low heat output
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high gas bills
And even worse?
Starved boilers die early. Period.
You wouldn’t starve a 400-hp engine and expect it to run right.
Same deal here.
Let’s go through the rules — Mike style — so you don’t choke your boiler to death.
1. The CGA-5 Needs the Right Pipe Size — NOT Whatever the House Already Has
Most older homes still have:
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½" black iron
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½" CSST
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long horizontal runs
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shared appliance tees
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rusted drip legs
NONE of that is acceptable for a 133,000 BTU atmospheric boiler.
Here’s the only rule that matters:
✔ ¾" pipe MINIMUM
✔ 1" pipe recommended for long distances
✔ 1¼" for extended manifolds or multiple branches
Why?
Because BTUs aren’t “magic heat.”
They’re gas volume multiplied by pressure.
The [Residential Gas Flow Pressure Drop Map] shows that ½" pipe cannot deliver enough volume beyond 20–25 feet, even under ideal pressure.
If your boiler is 30+ feet from the meter?
½" pipe is a hard NO.
¾" might work,
1" is correct.
2. Your Gas Pressure MUST Be Verified With a Manometer — Not Trust
This is the part that makes me snap:
Most installers never check gas pressure.
They “assume” it’s fine.
Here’s Mike’s rule:
✔ If your installer doesn’t pull out a manometer,
they’re not qualified to install a boiler. Period.
You MUST check:
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inlet static pressure
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inlet dynamic pressure (during firing)
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manifold pressure
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pressure drop across CSST (if used)
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pressure drop across any tees or elbows
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pressure stability during multi-appliance operation
The [High-BTU Appliance Manifold Stability Ledger] shows that boilers lose up to 15–30% firing capacity during low dynamic pressure events — which happen constantly in older homes with multi-branch gas lines.
If pressure drops under load?
Your flame shrinks.
Your BTUs disappear.
Your home never hits temperature.
3. Gas Appliances Upstream and Downstream Affect Your Boiler
A CGA-5 can’t operate properly if downstream appliances cannibalize gas volume.
Common offenders:
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tankless water heaters
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large dryers
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gas ranges
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older atmospheric furnaces
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fireplaces
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pool heaters
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generators
All of these create pressure waves and flow theft in the system.
The [Multi-Branch Gas Distribution Failure Study] shows that when multiple appliances fire simultaneously, branch systems can lose:
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0.2–0.8" wc
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up to 40% gas flow
Meaning:
Your boiler might fire at full input at 6 AM on a calm morning…
but drop to half-power at 6 PM when appliances pile on.
This MUST be accounted for during pipe sizing.
If the system is borderline?
Run a dedicated trunk.
4. Total Equivalent Pipe Length Matters — Elbows Are BTU Killers
This is the part homeowners never see:
Every elbow, tee, and bend drastically reduces gas flow.
Even “smooth” CSST has friction penalties.
Equivalent length matters MORE than straight length.
The [Gas Line Fittings and Equivalent Length Penalty Sheet] shows:
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A 90° elbow = 5–10 feet of “extra” pipe
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A tee run = 1–3 feet
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A tee branch = 10–20 feet
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A CSST bend = 5–15 feet (depending on radius)
Most older homes have dozens of elbows hidden in ceilings.
A system that looks like “25 feet of pipe”
is actually 80–120 feet of effective length.
This is why boilers starve even when “the pipe size looks fine.”
5. CSST (Yellow Flex Pipe) Has Massive Flow Limitations
Everyone loves CSST installers because they work fast.
But here’s what they never tell you:
✔ CSST has WAY higher friction loss
✔ CSST drastically reduces BTU capacity
✔ Long CSST runs starve boilers
The [High-Demand Appliance Capacity Test] reveals:
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¾" CSST carries less gas than ½" black iron in many runs
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some homes need 1" CSST just to match ¾" steel pipe
If your gas line is CSST and runs more than 30–40 feet?
You’re almost guaranteed to starve a CGA-5.
In that case, you need:
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1" CSST minimum
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or hard-pipe black iron
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or a dedicated supply trunk
Otherwise?
Your boiler will run weak forever.
6. Regulators, Meters, & Utility Supply Must Be Verified — Not Assumed
Many homes built before 1990 were never designed to handle modern BTU loads.
You must check the:
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gas meter BTU rating
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meter inlet pressure
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regulator condition
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outdoor regulator freeze protection
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utility supply pressure variance
The [Regulator Load Handling Report] found that older meters often max out at 150,000–200,000 BTU — barely enough to run a CGA-5 + water heater + range.
If the meter can’t keep up?
The boiler WILL lose firing rate.
This is why Mike ALWAYS tells homeowners:
“If we’re upgrading your boiler, we’re checking your meter — or the job isn’t done.”
7. A Drip Leg Isn’t Optional — It’s Your Boiler’s Insurance Policy
Natural gas often carries:
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moisture
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oil residue
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dirt flakes
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line debris
Without a drip leg:
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debris hits the gas valve
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ignition becomes unstable
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manifold pressure drops
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pilot issues occur
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flame sensor fouls
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valves stick
The [Gas Valve Contamination and Burner Reliability Study] shows gas valve contamination is a top cause of:
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failed ignition
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intermittent heat
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random lockouts
A drip leg costs $20.
Skipping it costs thousands.
8. The Boiler Needs a Dedicated Shutoff and Proper Union Placements
Not just for convenience —
but for SAFETY and combustion stability.
You need:
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boiler-only shutoff
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correctly placed union
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isolation from upstream vibration
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proper thread seal material
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correct approach length
Sloppy shutoff placement creates:
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micro-leaks
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pressure fluctuations
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vibration that affects the burner train
A CGA-5 is tough —
but even cast iron hates inconsistent gas delivery.
9. Mike’s Gas Line Sizing Formula (Simple Version)
Here’s the real-world rule:
133,000 BTU requires ¾" MINIMUM for up to ~30 ft equivalent length.
1" is mandatory beyond 30–40 ft.
1¼" if your home has multiple gas appliances on the same trunk.
This aligns with the [High-Demand Appliance Gas Flow Sizing Table], which proves that borderline gas piping destroys boiler performance.
10. Mike’s Final Verdict — Gas Starvation Is the #1 Boiler Killer
If you want your Weil-McLain CGA-5 to run like a beast —
with full flame, full BTU output, perfect combustion, and steady heat —
YOU MUST:
✔ Size the gas pipe correctly
✔ Check pressure under load
✔ Consider CSST friction
✔ Account for elbows & tees
✔ Verify upstream appliance demand
✔ Inspect the meter & regulator
✔ Install drip legs & shutoffs correctly
✔ Never “trust” existing pipe size
A boiler is only as strong as the gas line feeding it.
Feed it right, and it will run for 30 years.
Starve it, and it will act sick from day one.
That’s the Mike way.
Chimney Venting will be discussed in the next blog.
