Fire Pit Gas Line Sizing: How to Get It Right the First Time

By the Outdoor Heat Direct fire feature team · Authorized fire pit dealer · Reviewed September 2026

Why doesn’t the fire pit manufacturer tell me what size gas line to run?

Because the answer is not a property of the fire pit. It is a property of your house.

The manufacturer knows one of five variables: the burner’s input rating, usually 65,000 BTU/hr on the rating plate. The other four — distance from the gas meter, number of fittings, delivered pressure, and the total load of every other appliance on the system — belong to your property. A brand that printed “use 3/4-inch pipe” would be wrong for half its customers.

So every manual says the same thing: size the piping per NFPA 54, and have a licensed technician do it. That is not a dodge. The tables below are the ones your installer works from; read them and you can tell in ninety seconds whether a quote is plausible. Start with how many BTUs your fire pit needs.

How do I know my flame problem is the gas line and not the fire pit?

An undersized line has a signature. It is a pressure problem, and pressure problems track with demand. A burner that runs beautifully at 9 a.m. in July and sulks at 7 p.m. in January is telling you the pipe is too small, not that the burner is defective.

If the flame never arrives at all, work through the nine reasons a gas fire pit won’t light first. Sizing is the culprit when the fire pit lights but never performs — especially when performance changes as other appliances cycle.

What is the natural gas pipe capacity table?

This is the table. Schedule 40 metallic pipe, 0.60 specific gravity natural gas, inlet pressure under 2 psi, allowable pressure drop 0.5 inch water column — the standard low-pressure residential case. Capacity is in cubic feet per hour; at a nominal 1,000 BTU per cubic foot, multiply by 1,000 for BTU/hr.

Values as published in the National Fuel Gas Code sizing tables (ANSI Z223.1 / NFPA 54) and reproduced in adopted municipal fuel gas codes. Length is total equivalent length: manufacturer sizing charts commonly instruct you to add roughly 5 feet of equivalent pipe for every fitting.

Read it against a 65,000 BTU/hr fire pit — 65 cfh. A 1/2-inch line at 60 feet delivers exactly 65 cfh: not a margin, a coin flip, and only if the fire pit is the sole load on the pipe. At 100 feet, 1/2-inch drops to 50 cfh and cannot feed it at all. The same 100-foot run carries 104 cfh in 3/4-inch and 195 cfh in 1-inch.

Why is the propane table completely different?

Propane carries about 2,516 BTU per cubic foot against roughly 1,000 for natural gas, so the same 65,000 BTU/hr burner moves about 26 cubic feet per hour instead of 65. It also arrives at 11 inches water column rather than 7. More energy per cubic foot plus more pressure means a given pipe carries far more BTU on propane — which is why propane tables are published directly in BTU/hr. This one covers Schedule 40 pipe downstream of the second-stage regulator, capacity in thousands of BTU per hour.

Second-stage sizing table per NFPA 54 / NFPA 58 as published by regulator manufacturers. Multiply by 1,000 for BTU/hr. First-stage piping between the tank and the second-stage regulator operates at a much higher pressure and is sized from a different table entirely.

Same fire pit: a 1/2-inch propane run still delivers 84,000 BTU/hr at 100 feet, where natural gas in that pipe failed long ago. It is an underrated advantage of tanks, covered in the natural gas vs. propane comparison. It does not make 1/2-inch automatically correct — it means pipe is rarely the binding constraint on a dedicated propane run. Tank vaporization rate in cold weather usually is.

Do I size the line for the fire pit or for the whole house?

For the whole system. This is the point that breaks the most installations, and the one almost nobody explains.

NFPA 54 sizing is a longest-length calculation across the whole system, starting at the meter. Every section must carry the total demand of everything downstream of it, over the distance from the meter to the most remote outlet. A 3/4-inch trunk that was adequate for a furnace and water heater in 1998 is a different pipe once a range, a dryer, a grill and a 65,000 BTU/hr fire pit hang off it.

Build the list before the technician arrives, reading each rating off the appliance plate — not off the internet, not off memory:

• Furnace, water heater and clothes dryer — each from its rating plate
• Range or cooktop — all burners plus oven
• Built-in grill or outdoor kitchen
• The new fire pit — 65,000 BTU/hr on most 36–48 in. models

Six ordinary appliances routinely total 300,000–400,000 BTU/hr. At 60 feet from the meter, 3/4-inch pipe carries 137 cfh — about 137,000 BTU/hr. Not close. That is why the fix for “my new fire pit has a weak flame” is often a larger trunk line, not a new burner. If the fire pit is part of a patio build on pavers or a concrete slab, settle this before anything is poured.

Does black iron, CSST, copper or PE change the capacity?

Yes, substantially — and the nominal size on the label misleads you. Black iron pipe is the reference case; the numbers above are its numbers. CSST — corrugated stainless steel tubing, the yellow or black jacketed flexible product — is sized by EHD (Equivalent Hydraulic Diameter) rather than nominal size, and carries materially less. From one manufacturer’s published natural gas tables at 0.5 in. w.c. drop:

CSST values from one manufacturer’s published sizing tables. CSST capacity tables are manufacturer-specific and are not interchangeable between brands — the installer must use the table for the product actually installed. Black iron values in the right-hand column are from the table above.

At 50 feet, 3/4-inch CSST delivers 87 cfh where black iron delivers 151. The corrugations that make it flexible also make it turbulent. An installer who substitutes CSST at the “same size” to save labor has quietly cut capacity by roughly 40 percent.

Copper is permitted for propane in most jurisdictions and prohibited for natural gas in some, because sulfur compounds in odorized gas attack it; sized by outside diameter, 1/2-inch copper has a much smaller bore than 1/2-inch pipe. Polyethylene (PE) is the yellow plastic used for buried yard runs — it must transition to metallic pipe before coming above grade, needs a tracer wire, and cannot be used indoors.

What should I have ready before the installer arrives?

Seven numbers. Have these on paper and the first visit becomes a quote instead of a survey — and you will know immediately whether the person in your driveway is calculating or guessing.

Add one item that is not a number: how many elbows and tees the route requires. Fittings add equivalent length, and manufacturer sizing charts commonly count roughly 5 feet of pipe per fitting. A 40-foot run with eight fittings is sized as though it were 80.

What does it cost to run a gas line to a fire pit in 2026?

National 2026 ranges, before regional labor variance:

• Installed gas line: $15–$50+ per linear foot. Simple, accessible runs land at $15–$25; complex work runs $35–$50+.
• Typical outdoor grill or fire pit line: $600–$1,300 all-in.
• Open trenching: $5–$15 per linear foot.
• Horizontal directional boring: $10–$30 per linear foot — roughly double trenching, but it goes under a driveway or finished patio without tearing it up. On a finished landscape it is often the cheaper option once restoration is counted.
• Permit: $100–$300+ depending on jurisdiction.
• Pipe material: black iron $5–$10 per foot, CSST $2–$10, HDPE $1–$3.

Look at that last line and the upsizing decision answers itself. Local rules vary widely on burial depth, tracer wire, sleeving under hardscape and shutoff location — our fire pit regulations page covers what differs by jurisdiction.

Should I run a bigger pipe than the calculation requires?

Usually yes, and it is the cheapest decision in the project. The pipe is the small line item; trenching, boring, permits and labor are the job. Stepping from 3/4-inch to 1-inch black iron adds a few dollars per foot on a project where the trench alone costs $5–$15 per foot — and it nearly doubles capacity at 50 feet, from 151 cfh to 284 cfh. That margin lets you add an outdoor kitchen, a pool heater or a second fire feature later without opening the ground again. Tell your installer which future appliances are plausible and have them size for the eventual load. Ask for the calculation, not just the pipe.

While the trench is open, settle the rest of the gas side: the burner style, match-lit or electronic ignition, and where the shutoff goes. Most match-lit installations use a key valve set within reach but outside the required clearance envelope.

Frequently asked questions