Need a gas connector for your water heater, fireplace, stove, etc.? Learn how to choose the right one and protect both your family and your investment..

How to Size a Gas Flex Connector

When a gas appliance is replaced, you might think it's fine to reuse the flexible, corrugated connector (aka supply line) that connected the old unit to the home's gas supply. It's not - many plumbing codes and most manufacturer guidelines prohibit their reuse. As you might guess, this has everything to do with safety - namely, preventing leaks. Crushed threads, kinks, or damage incurred during appliance removal can lead to a dangerous situation once gas starts flowing again. Worse yet, leaks aren't always immediate after this kind of damage, making safe reuse more than a matter of a simple soapy water test after installation.

New appliances may come with a gas connector, but that's not terribly common. Chances are you'll have to purchase one independently. And clearly if your existing connector is damaged or severely bent/kinked, you need to replace it ASAP. If you're lucky, the old connector may still have a tag giving you the details you need to make the right selection. Should that not be the case, we're here to help!

Note: If the room's gas line doesn't have a service (or shutoff) valve, one must be installed. A valve at the appliance allows for easy servicing (you won't have to go to the meter or tank to turn off the supply) and safer operation.

Sizing the Connector

  • The first thing to do is to measure the distance between the gas pipe and the appliance. Add at least 3 inches to that distance to allow for movement and shifting of the appliance: this is the connector length you'll need to look for. Don't get something too long or too short, as this only invites bending and kinking.
  • Next, you'll need to consult the appliance or its documentation to find out how much gas is going to be used. Gas appliances (propane or natural gas) have a maximum BTU (British Thermal Unit) input that must be satisfied by the connector. A gas range, for instance, requires a connector that can supply the amount of gas used when all burners are on high, with the oven on.
  • The BTU capacity of a connector changes as the line increases in both diameter and length. The larger the inside diameter, the greater volume of gas that can flow through it. However, as the connector's length increases, that maximum volume decreases. So a 1/2" ID connector that's 12" long can provide a maximum of 180,000 BTU of natural gas, while a 24" connector of the same diameter only provides 150,000 BTU. On our site you'll find the BTU capacity in each of our listings; if you're in a store, they can be found on the product packaging. Be sure to round up from the appliance's BTU input.

    Watch Out! Connector BTU capacity also depends on the type of gas being used: natural gas (NG) capacity is always lower than liquid propane (LP) capacity. This means that the same hose will provide more BTU using LP than NG - so make sure you're looking at the right number!

  • Finally, you'll need to determine the proper connection type and size -- how the ends of the connector join to the appliance and gas supply. This should be indicated on the appliance, in documentation, or you can simply match the old connector if still available.

Determining Connection Size

If you're unable to find the size or type of connection required, don't worry! It's fairly simple to figure out. Gas connections are made using either NPT (F/M/IPS) threads, or a flare connection. Flares are easily identified by their unique semi-conical end, while NPT threaded connections are the same threads you see throughout most plumbing.

Use calipers or a tape measure/ruler to measure the outside diameter of threaded connections according to this reference page (and the below graphic). Male threads are measured as shown in A, female threads as shown in B. The measurement is only the first part, though: the number you arrive at must be located in column 1 or 2 of the reference table, and its corresponding NPT size found in column 3. For example, male threads measuring 27/32" across translate to a 1/2" NPT size - if female, we usually refer to this connection as 1/2" FIPS; if male, 1/2" MIPS. NPT and IPS (Iron Pipe Size) are interchangeable.

Using your eye and a standard tape measure, what you actually observe will probably be closer to 13/16", so you may have to round up or down to the nearest reference fraction on our table. Our 13/16" eyeball figure can be increased to 26/32 by multiplying both sides of the fraction by 2; similar math may be required to find the proper connection size. All of this is of course quickly remedied with the use of calipers - especially digital ones!

If you have a flared connection to make, simply measure the outside diameter of the threads according to figs. A or B - no conversion is required.

Pro Tip - Keep an eye out for gas appliance connector kits, which include everything you need to hook up whatever you're installing. We offer several commercial kits that include connectors, fittings, adapters, valves, and restraining hardware. If you need only a valve with your connector, you can purchase the two as a complete set.

Safety Features

Once you've figured out what's needed, it should be no problem to find a basic connector. As with most any product, there are additional features that are worth considering. Many features are found primarily in commercial connectors, but keep in mind that these can still be used around the house - provided the connector fits. Basic connectors are perfectly safe for residential use, but those seeking additional peace of mind will appreciate some of the safety and mobility features available.

  • Common enough to be standard these days, PVC plastic coating helps protect connectors from the eventual threats of corrosion. Some coatings are even antimicrobial, inhibiting bacteria, mildew and mold growth.
  • Thermal safety shutoffs are a typical commercial connector feature, which close off gas flow at high (350°F+) internal temperatures.
  • The SwivelMAX adapter for allows for vastly increased movement and positioning of the connector and the appliance - especially helpful in cramped kitchens and for awkward appliances.
  • SnapFast adapters utilize push-to-connect technology to allow for quick and secure one-handed connection and removal. These also include a thermal shutoff feature.
  • Safety valves like the Safety Quik can't be opened until a connector is attached, and connectors cannot be disconnected until the valve is shut off - preventing accidental disconnection and damage. Safety Quiks also feature SnapFast connections and a thermal shutoff.

Don't forget to add gas-rated PTFE tape (typically yellow) and thread sealing compound for the connector installation (unless you're dealing with a flare connection, where these can actually compromise the connection). If you aren't quite sure how or where to turn off the gas supply, find out here.

Start shopping for your new gas supply line right now!

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