Pipe Sizing for Home Standby Generators
Fuel pipe sizing is one of the most important aspects of generator installations and knowing the right size to go with will keep your generator running properly.
Generator manufacturers typically have pipe sizing charts based on the generators output wattage and the distance from the fuel source. Some manufactures recommend consulting with your installing plumber to make the right pipe size selection based on their knowledge and according to local codes.
When a pipe is sized too small, the generator will not get a sufficient amount of fuel. This causes the engine to starve, preventing it from starting. The engine will try and try, but after several start-up attempts the unit will quit and sound an alarm to alert you there is something wrong.
There are many references for fuel pipe sizing, such as NFPA 54 – Natural Gas Fuel Code, 2006 (Item# 320-6031-06) which is a commonly used resource for certified plumbers. Some of these references can be found online.One of the best methods of installation is to oversize the piping, allowing sufficient flow to the unit and giving it more than enough fuel.
Your installing plumbing should consider the specific gravity of the gas and compensate for a nominal amount of restrictions from bends, fittings and T’s. If an extensive amount of these restrictions are used you will need to refer to federal and local codes for proper sizing information.
The generator needs to be the first item connected to the fuel source. A home standby generator will start operating at full load capacity allowing it to handle the large starting loads. If the generator is not the first item within the system, it can create enough suction/vacuum in the fuel line to stop any flow to other appliances ahead of it. This can cause issues with pilot lights, such as heating systems, if you are not home to relight them.
Other information that your installing plumber may need is the BTU requirements of the home standby systems. This is easy to calculate, and the information is readily available in the manufacturers’ spec sheets. Here are some examples of how to convert fuel consumption to BTU:
Example 1: A 20kW Generac model 6244 has full load natural gas consumption: 308 FT3/HR (Cubic Feet per Hour). You can take that number and multiply it by 1000 to get 308,000 BTU/HR (BTU per Hour)
Example 2: A 20kW Generac model 6244 has full load Liquid Propane Vapor Consumption: 3.85 GAL/HR (Gallons per Hour). You can take that number and multiply 3.85 by the BTU per gallon (91,547 estimated) to get 352,456 BTU/HR (BTU per Hour).
Due to the many factors with pipe sizing, we always recommend consulting with your local certified plumber for installation assistance and the manufacturer’s installation guides.