Installation Guide

Gas Pipe System Sizing
Determining the Required Meter and Regulator size.
Find the BTU requirement of each appliance in the home. In our example above, we have the following:
199,900 BTU Tankless, a 75,000 BTU Furnace, a 55,000 BTU Range, a 25,000 BTU Dryer, and a 40,000 BTU Gas Log Fireplace. The
sum of these appliances is 394,900 BTU. Since most gas regulators and meters are rated in Cubic Feet per Hour, we need to con-
vert the BTU calculation to ensure they are sized correctly. Divide total BTU by 1,024 to get the estimated Cubic Feet per Hour (CFH)
requirement for the meter and regulator; 386 CFH in our example.
If the water heater was a typical tank type at 40,000 BTU, then the overall system requirement would have been just 235,000 BTU with
a meter and regulator rated at 235 Cubic Feet per Hour. A typical household meter and regulator is commonly rated at 250 Cubic Feet
per Hour. As you can see that in the example above, when you change the water heater to a tankless, the existing regulator and meter
would be potentially undersized. It is important to have a properly sized meter and regulator on the system; otherwise, the appliances
on the system could experience operational issues. The local gas utility can provide more information on upgrading the meter and
regulator for the home.
Hybrid pressure systems, with a 2 psi static pressure with regulators at each appliance, are sized differently than in this example. Con-
sult your local gas supplier or the National Fuel Gas Code in regards to these type systems.
Pipe Sizing Methods
There are two basic pipe sizing methods: longest length and branch length. Proper sizing will allow the system to maintain the required
minimum pressure drop.
In the longest length method, the pipe size of each section should be determined by using the longest length of piping from the point
of delivery, the gas meter or regulator, to the most remote outlet and the load of the section.
In the branch length method, the pipe size of each section of the longest pipe run, from the point of delivery to the most remote outlet,
should be determined by the longest run of piping and the load of the section. The pipe size of each section of branch piping should
be determined using the length of piping from the point of delivery to the most remote outlet in each branch and the load of the sec-
tion. Branch length sizing is the most common method.
Furnace
(75,000 BTU)
Tankless Water Heater
(199,900 BTU)
Gas Range
(55,000 BTU)
Gas Dryer
(25,000 BTU)
Gas Logs Fireplace
(40,000 BTU)
20 ft
15 ft
30 ft
20 ft
30 ft
15 ft
30 ft
20 ft
10 ft
Branch 1 Total
274,900 BTU
Gas Meter
(395 Cubic Feet)
A
B
C
D
E
G
H
J
K
Figure 1 - Typical Gas System with a Tankless Water Heater
Branch 2 Total
120,000 BTU
Trunk Line Total
394,900 BTU
The information in this brochure is for educational purposes only, it is not meant to be an engineering guide or supplement any national or local code. All national and local
codes muse be followed. The information in this brochure was obtained from the National Fuel Gas Code, NFPA54, ANSI Z223.1 2012 Edition. Refer to the National Fuel
Gas Code, your local gas supplier, or your local code official for information. Gas systems should be designed, installed, and inspected by a certified and licensed gas fitter,
engineer, or tradesman. The information in this guide does not apply for installations in Canada, see CAN/CSA B149.1 for details or consult with your local code official.