The size of the propane gas line for a tankless water heater is a critical factor in ensuring the proper operation and performance of the unit. Tankless water heaters have a high demand for gas, and the gas line must be sized correctly to provide sufficient gas supply to the burner. Improper gas line sizing can lead to poor performance, reduced efficiency, and even damage to the tankless water heater.
Factors Affecting Gas Line Size
The size of the propane gas line for a tankless water heater depends on several factors, including:
-
BTU Input of the Tankless Water Heater: The BTU (British Thermal Unit) input of the tankless water heater is a crucial factor in determining the required gas line size. Tankless water heaters typically have a higher BTU input compared to traditional tank-style water heaters, which means they require a larger gas line to meet their gas demand.
-
Length of the Gas Piping System: The length of the gas piping system, from the gas meter or propane tank to the tankless water heater, also affects the required gas line size. Longer gas lines require a larger pipe diameter to maintain the necessary gas pressure and flow.
-
Number of Appliances on the Gas System: If the tankless water heater is not the only gas appliance on the system, the total gas demand of all the appliances must be considered when sizing the gas line. The gas line must be sized to accommodate the combined gas demand of all the appliances.
-
Pressure Drop: The pressure drop in the gas piping system, caused by friction and other factors, can also impact the required gas line size. The gas line must be sized to maintain the minimum required gas pressure at the tankless water heater, even with the pressure drop.
Recommended Gas Line Size
As a general rule, most tankless water heaters require a 3/4-inch gas line to provide a sufficient gas supply to the unit’s burner. This size is recommended for most residential and light commercial applications.
However, the specific gas line size required for a tankless water heater can vary depending on the factors mentioned above. The National Fuel Gas Code (NFPA 54), ANSI Z223.1, and the Natural Gas and Propane Installation Code (CSA B149.1) provide detailed guidelines for sizing gas lines based on these factors.
For example, according to the National Fuel Gas Code, a 200,000 BTU tankless water heater would require a minimum of a 3/4-inch gas supply line. In specific conditions, a 1/2-inch gas line may be used for a length of up to 40 feet, provided that the minimum static gas pressure is 8 inches of water column (in. w.c.) or greater, and the calculated pressure drop is greater than the highest minimum gas pressure required by any of the gas appliances on the system.
Determining the Correct Gas Line Size
To determine the correct gas line size for a tankless water heater, you can use the following methods:
-
Longest Length Method: This method involves determining the required pipe size of each section and outlet of the piping system based on the longest length of the piping system.
-
Branch Length Method: This method involves determining the required pipe size based on the length and number of branches from the gas meter or propane tank.
When using these methods, it is essential to consult the National Fuel Gas Code, ANSI Z223.1, or the Natural Gas and Propane Installation Code, CSA B149.1, for the appropriate tables and calculations.
It is important to note that gas system design, installation, and inspection should be performed by a licensed professional to ensure compliance with local codes and regulations. A licensed professional can help determine the correct gas line size based on the specific requirements of the tankless water heater and the existing gas system.
Conclusion
The size of the propane gas line for a tankless water heater is typically 3/4-inch, but it can vary depending on the specific factors of the installation, such as the BTU input of the heater, the length of the piping system, the number of appliances, and the pressure drop. It is essential to consult with a licensed professional to ensure that the gas line is properly sized and installed to meet the demand of the tankless water heater and comply with local codes and regulations.
References:
– Rinnai Tankless Water Heaters – 1/2″ Gas Line Piping Information (as per ANSI Z223.1-2015) Sizing: https://media.rinnai.us/salsify_asset/s-f905168b-b0a9-4b7c-a205-bbb8071597bb/TB-111%20Half%20Inch%20Gas%20line.pdf
– Reddit – Gas line size for tankless water heater: https://www.reddit.com/r/Plumbing/comments/10splc8/gas_line_size_for_tankless_water_heater/
– Thrifty Supply – RTG-Gas Piping Facts: http://users.snowcrest.net/thriftysupply/pdf/RTG-Gas_Piping_Facts.pdf