Gas piping guidelines backup electrical generators & other emergency electrical power sources for residential & light commercial use:

Using advice from Generac™ and other backup electric generator installation manuals here we give examples of generator gas piping size, lengths, regulator and pressure requirements & settings.

This article series discusses the use of emergency generators for electrical power backup at residential properties. We describe how to determine how much back up generator capacity or power in watts you'll require.

Gas Supply for LPG or Natural Gas Fueled Backup Electric Generators

How to solve fuel-starved electric generator: regulators "fighting" for fuel

2018/07/24 David Morris said:

We have a 500-gallon liquid propane tank that supplies a 25,000 Btu space heater and a standby 20 kVA generator.

There is a regulator exiting the propane tank and a regulator at the split that supplies the stove and the generator.

Frequently, when the generator is running in case of a power outage, the generator will "surge", causing the lights to flicker and this is not good for motors or electronics.

I have on several occasions noticed the two regulators "fighting each other" and I learned in school that you can't put two pressure controllers back-to-back and expect either of them to work.

Is there some method using orifice plates to regulate the pressure between the tank and the second (house) regulator to maintain the requisite pressure at the upstream side of the house regulator with a "control action"?

The image shows a typical LPG regulator on a Generac LP gas fueled generator

Source: GENERAC® 8-22 kW AIR-COOLED GENERATORS INSTALLATION GUIDELINES [PDF] (2014) cited in detail below.

This Q&A were posted originally

at GAS PRESSURES LP vs NATURAL GAS

5 Steps to fix gas regulator surging / fighting for your 20kW backup electric generator

David

Fixing Inadequate LP Gas Supply to an Electrical Generator

An authoritative answer should come from your gas supplier as I'm uncertain myself of the right solution.

But I suspect that the regulators are not properly placed, pressures are set wrong, or the gas piping is too small. Less common is an under-sized LPG tank itself. (250 gallon is a common minimum size).

1. Check the gas regulator size, capacity, and location

Check the placement (and of course presence) of both primary and secondary regulators

Typically a first stage gas pressure regulator is installed at the tank (or at the gas meter if you are using natural gas0 and an additional regulator is installed at or even inside of each gas appliance.

Also typically, backup electrical generators require that the primary or first stage gas pressure regulator be purchased and installed separately. It is not provided with the generator.

But the backup generator will normally include its own second-stage gas regulator. You may need to set or adjust the regulator to the proper fuel being used: NG (natural gas) or LPG (propane).

But check your generator's instructions for the location of that second-stage regulator.

Your plumber will need to check the delivery capacity of the primary stage regulator against the total possible LPG demand.

A 20kW Generac electric generator will require a flow rate of and will use 3.85 gallons of LPG or 14.57 liters of LPG per hour.

As you'll see in our gas piping distance tables below, the location of the generator itself will affect the required pipe diameter as well.

2. Check the gas piping diameter, length, elbows vs generator size & fuel type

Next, it may be that the diameter of the gas piping is improperly sized for the required flow rate or for the distance the fuel has to travel.

That too can cause the problem you describe - the gas supply and pipe must be sized at 100% Load BTU / megajoule rating. I’ve read that under-sized gas supply piping is one of the most common mistakes made in LPG generator installation.

• For a 20kVA gas-fueled Generac™ electric generator, typically the pipe is 3/4” ID (interior diameter).
• Smaller Generac™ generators, in the 8-16kW range typically use 1/2" ID piping.

In the installation manual for your generator you will probably see a table that gives the allowable total distance of piping that can work for several pipe diameters. You’d also have to take into account the number of bends or elbows or restrictions.

Watch out: the piping and regulator requirements are different depending on whether a generator is fueled by the lighter natural gas or heavier more-dense LPG.

EXAMPLE: 20kW Generac LPG-fueled generator using a 3/4” diameter gas line can run just 15 feet of pipe. To go to longer distances (up to 115 ft or 35meters) you’d need to use a 1” diameter gas line.

While you’re looking at the gas piping, also check for improper bends in the piping.

Watch out: Generac warns that you should never bend the flexible final connecting fuel line to avoid using an elbow. Doing so interferes with the line’s ability to absorb vibration. The result could be a dangerous gas leak.

Generac's instructions include a table of LP Vapor Pipe sizing that I found a little confusing. Below we provide the same data with a bit more labeling to make the data easier to read

Watch out: review and follow the instructions in the installation manual for your specific generator as those requirements could certainly be different. The following example tables are for general information only.

Notes to the table above

Source: GENERAC® 8-22 kW AIR-COOLED GENERATORS INSTALLATION GUIDELINES [PDF] (2014) cited in detail below. Generac warns that

Watch out: The gas supply and pipe MUST be sized at 100% Load BTU / megajoule rating. - op. cit. p. 22.

Pipe sizes in these tables are for installations that are using a second stage regulator. - op. cit. p. 22.

The minimum LP tank size is 250 gallons (946 L), unless unit calculations dictate use of a larger tank. Vertical tanks, which are measured in pounds (or kilograms), will not usually meet the minimum tank size requirement. A 1050 lb (476 kg) vertical tank size minimum is required. - op. cit. p. 22.

The backup electric generator, when running on LP rather than natural gas, uses LP or liquid propane but only with actual gas vapor inlet, no liquid.

Pipe diameters are normally ID or inside diameter. For example a 1 1/4" ID pipe will have a larger OD or outside diameter that varies depending on the pipe wall thickness that in turn depends on the pipe material.

Watch out: these generator gas pipe size and length constraints are for propane-fueled generators.

For Generac™ systems the required fuel pressure for for liquid propane vapor is 10 to 12 in water column (19 to 22 mm Hg mercury).

If your generator is using natural gas different tables, sizes, and distances apply. Check and comply with the manual for your generator.

Below the table gives example piping distances that will work for Generac™ backup generators in the 8-22 kW range for various pipe sizes.

3. Check gas regulator pressure adjustments

Possibly your gas pressures are not properly adjusted even if the pressure and delivery and pipe diameters are adequate.

Here is an excerpt from the same example LPG Generac Generator Manual - with the WARNING: Watch out: this is an example from a specific Generac LPG fueled electrical generator manual. I do not have a shred of information bout your specific generator brand, model and specifications, and they may well be quite different.

• Required fuel pressure for natural gas is 3.5-7 in water column (7-13 mm mercury).
• Required fuel pressure for for liquid propane vapor is 10-12 in water column (19-22 mm mercury). [This is your case]
• The primary regulator for the propane supply is NOT INCLUDED with the generator. - GENERAC® 8-22 kW AIR-COOLED GENERATORS INSTALLATION GUIDELINES cited and linked to above and also
  
  at MANUALS for BACKUP GENERATORS

4. Check for debris blockages in the fuel system

If everything is properly sized and adjusted but gas flow is inadequate there could be debris clogging at a regulator, screen, or even in a pipe length, at a shutoff valve, or elbow.

Depending on the quality of fuel and type of fuel, some installations require a sediment trap at the regulator.

5. Check fuel type settings: LPG vs Natural Gas

Unlikely since I think your generator wouldn’t work if the wrong fuel-selection settings were used, but double-check that the proper fuel type (LPG or NG) has been selected on your generator (that’s assuming that like Generac models your generator has a simple fuel knob that allows selection of the proper fuel; on other equipment one might have to change a regulator and gas orifices).

Generac generators arrive from the factory set to use NG (natural gas). An orange "fuel conversion" knob switches between NG (natural gas) and LP (liquid propane).

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

OK to Use CSST Gas Tubing to a Standby Generator?

Can you use CSST to supply a standby generator as long as it is a dedicated line and has excess supply capacity for the generator. - On 2022-11-17 by Dennis

This Q&A were posted originally

at GAS PIPING, FLEXIBLE CSST

Reply by InspectApedia (Editor) (mod) - NO don't connect CSST gas piping directly to your standby generator

@Dennis,

As Mark Cramer says ... it depends.

You can NOT use CSST to connect to a portable generator - there is too much movement and vibration.

The illlustrations we show here are from

• GENERAC® 8-22 kW AIR-COOLED GENERATORS INSTALLATION GUIDELINES [PDF] (2014) Generac Power Systems, Inc., S45 W29290 Hwy. 59 Waukesha, WI 53189 USA Tel: 1-888-GENERAC (1-888-436-3722)
  Website: generac.com

Watch out: note that the gas piping type name "CSST" does not appear in this manual nor in other generator manuals we've reviewed.

Typical backup generator instructions state about the flexible fuel line:

Flexible Fuel Line

• Do not bend!!!
• Do not attach directly to generator
• Check all connections for leaks

The risk of a gas leak is, of course, a fire or explosion.

To make a connection between a generator and the gas supply you need to

1. follow the generator manufacturer's instructions with care, and completely

See MANUALS for BACKUP GENERATORS

2. use the connectors, including any manufacturer-supplied flexible connection, following instructions in the manual supplied with the equipment.



In sum, you can deliver gas TO the SITE of the standby generator using CSST but depending on the generator size, type, portability, AND its manufacturer's instructions, you may need a flexible connector.

Watch out: there are additional stand-by electrical generator installation requirements that are essential for safety such as

- proper installation and use of a transfer switch

- proper electrical grounding and bonding

- independent, dedicated gas supply to the generator of adequate size to handle the generator's need at full load

- properly located and installed "full flow" type gas shutoff valve in the gas piping

- use the manufacturer's supplied (and thus approved) flexible gas line

PLEASE SEE

GAS SUPPLY for ELECTRIC GENERATORS - the article above on this page

Thank you for a helpful question.

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Continue reading  at GAS PRESSURE FLOW INADEQUATE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BACKUP ELECTRICAL GENERATORS
• ELECTRIC GENERATOR CAPACITY REQUIREMENTS - separate article
• HOW TO WIRE UP an ELECTRIC GENERATOR
• ISOLATION SWITCH REQUIREMENTS
• DOUBLE THROW TRANSFER SWITCH
• AUTOMATIC TRANSFER SWITCHES
• ELECTRICAL GROUNDING for GENERATORS
• PORTABLE ELECTRIC GENERATOR CLEARANCE DISTANCES
• CAR or TRUCK 120V GENERATORS
• GAS PRESSURE FLOW INADEQUATE
• GAS SUPPLY for ELECTRIC GENERATORS
• HOW TO TURN ON / OFF a BACKUP GENERATOR
• MANUALS for BACKUP GENERATORS
• WHERE TO BUY of 12-volt to 120-volt DC to AC power converters & inverters
• WHERE TO BUY ELECTRICAL GENERATORS - separate article
• GAS REGULATORS & APPLIANCE / HEATER CONTROLS
• GAS PRESSURES LP vs NATURAL GAS
• GAS REGULATORS for LP TANKS

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