I am remodeling two of the apartments in a 3-unit apartment building that I
own. It's a 3-floor building with one apartment on each floor. All of the
utilities are separate, so each apartment pays all of their own utilities
including heat, hot water, cooking gas, and electric.
The bottom floor also has a separate room for the 3 gas heaters/boilers for
each unit's hot water baseboard heat, and the 3 gas hot water heaters.
There are also 3 gas meters down there-- one for each apartment.
What I want to do is move and replace the gas lines that now go to the 3
heaters/boilers, 3 hot water heaters, and the 3 gas cooking stoves/ovens.
As far as I can tell, most of the existing gas supply lines that I will be
replacing are way bigger than they need to be, so I am trying to figure out
if I can replace them with smaller size black iron pipe.
My basic question is: "What size black iron gas pipes do I need for the
Here are some additional details:
1) The main gas supply line coming into the building looks like it is about
1-1/2 inch black iron pipe. It's possible that it is 2 inches (I forgot to
measure it before posting this).
2) The main gas supply line has 3 gas meters coming off of it -- one for
3) Looking at the fittings that come out of the gas meter for each unit, it
looks to me like there is a reducer fitting on each one with the smallest
end of the reducer fitting being 1/2-inch, I think (but possibly 3/4-inch at
most -- I'll double check).
4) All 3 units have black iron pipe gas supply lines AFTER the meter that
are about 1-1/2 inch each.
5) Each unit's 1-1/2 inch gas supply line then splits off and supplies: one
100,000 BTU gas heater/boiler, one 30-gallon gas hot water heater, and one
24-inch apartment size gas cooking stove and oven.
I know that with water lines, once the main line is reduced down to a size
of say 1/2-inch, making any lines past that reduction point larger than
1/2-inch is pointless because the maximum flow has already been reduced the
1/2-inch. Do natural gas lines work the same way? In other words, if the
pipe line coming out of the gas meter goes through a reducer fitting that is
no larger than 1/2-inch, does that mean that any pipes after that point do
not need to be any larger that 1/2-inch?
I'm using the "logic" that there is no point and no need to replace the
existing lines with pipe that is any larger than the size to which the gas
line coming out of each meter has been reduced. Is that correct?
Or, to look at it another way, if a natural gas line is split to supply 3
things -- a 100,000 BTU gas heater/boiler, and 30-gallon gas hot water
heater, and a 24-inch apartment size gas cooking stove and oven -- what size
does it need to be? Will 1/2-inch black iron pipe or 3/4-inch black iron
pipe be sufficient throughout that system for each unit?