Installation of a gas range requires running a new gas line from the
basement utility room to the kitchen, a total of about ten feet. The
installation instructions indicate either a 1/2 or 3/4-inch line can be
used. The easiest approach would be to tee black pipe into an existing
1/2-inch gas line feeding a 40 gal/40,000 BTU gas water heater. Will the
1/2-inch line now feeding the water heater have enough capacity to support
both the water heater and a gas range? The combined BTU of all the range
burners is about 60,000 BTU. Opinions?
No. Run a new line from the source to the range.... the source being
at least a 3/4" line, but preferrably a 1" line.
You don't want your water heater to have a drop in volume (and
pressure, but volume is important), causing a low flame or for the
pilot to go out. The smaller the line, the less volume the same
pressure will move vs the larger the line, the more volume the same
pressure will move.
You said it right, "capacity", meaning volume, as opposed to
pressure. The source (your meter manifold) has a regulator to
automatically maintain constant pressure.
You don't say how long the existing half inch line to the water
heater is. That will be important.
Having said that, I think this would be very marginal. It might
work. But it might not.
Is that where you want to be? Guessing and hoping?
In your shoes, I would run some new pipe.
| Malcolm Hoar "The more I practice, the luckier I get". |
You need to count the fittings and the lengths of pipe from the gas
meter to the water heater tee and then from the water heater tee to
your range. Then you need to do some math to answer your question.
Long answer (the math):
I'm going assume you are talking about natural gas and that your
utility provides gas with a specific gravity of 0.60, and that the
heat content of your natural gas is 1000 BTU per cubic foot. These
are common values. By convention, the natural gas pressure after the
meter is 7.0" w.c., and the natural gas piping system needs to be
designed for a total pressure drop of 0.5" w.c. or less from the meter
to each appliance.
Now in measuring length of iron pipe for natural gas distribution, you
need to include each fitting via its equivalent length. When I google
"natural gas equivalent length 90", the first hit gives me a chart
with the appropriate values. For example, a 1/2" 90 degree bend is
equivalent to 1.55 feet.
So what you need to do next is to follow the iron pipe running from
the meter to the tee by your water heater. Add up the fitting
equivalent lengths to the lengths of the straight runs to get a total
equivalent length, call it X1. Here I am assuming the water heater
run is all 1/2" pipe and has no other outlets.
Now figure out the proposed run from the tee by your water heater to
the gas range location, including all fittings, and determine its
equivalent length, call it X2. With the fittings counted, X2 will be
greater than the 10' you specify.
The last piece of info you need is the pressure drop per unit length
for 1/2" iron pipe at flow rates of 100 cubic feet/hour (from the
meter to the tee for both appliances) and at 60 cubic feet/hour (from
the tee to the range). Those are 0.0183 and and 0.0071, respectively.
I got these from the page 77 of the design guide for the CSST I use,
Then your pressure drop will OK if 0.0183 * X1 + 0.0071 * X2 < 0.5.
For example, if X2 = 20' after you include the fittings, then the
pressure drop on that leg would be 0.142" w.c., and so to be OK you
would need 0.0183 * X1 < (0.5 - 0.142), or X1 < 20'. For other
cases, you can do the math.
Note that if your pressure drop calculation is close to but above 0.5,
you could try 3/4" pipe from the water heater tee to the range
location. You'll need to refigure X2 using the new equivalent lengths
for 3/4" fittings. And you'll need the pressure drop per foot for
3/4" pipe at 60 CFH, which is 0.0018.
So if the new run is 3/4" you need 0.0183 * X1 + 0.0018 * X2 < 0.5.
Also, note that if X1 > 0.5/0.0183 = 27' then you're out of luck
tieing into that tee by your water heater, the line to the water
heater simply can't handle 100 cubic feet/hour. You'll have to run a
new line all the way from the meter. As long as its equivalent length
is less than 0.5/0.0071 = 70', you can use 1/2" pipe for it; with 3/4"
pipe, the equivalent length can be up to 0.5/0.0018 = 280'.
Wow, Wayne, that was the long answer. :)
And the absolutely "correct: way to calc oneself to the answer but
there is a way to get there with a lot less work and typically
fittings dont matter all that much.
A while back I think Ed posted a great on natural gas piping system
design / analysis link from the city of Newark, CA.
It showed a pretty simple means to size a gas delivery system but they
have since moved or removed the page. :(
Looks like the city of Pleasanton has come to the rescue.
Their example looks a bit complicated at first but basically you just
map out the pipe lengths
& sizes making sure at each branching that the piping upstream can
deliver the gas required at that point.
Here's a gas supply capacity table (if the format holds)
Capacity of Pipe (MBH ≈ CFH)
Pipe Size (in) Pipe Length (ft)
Nominal Inside diameter 10 20 40 80 150 300
1/2 0.622 120 85 60 42 31 22
3/4 0.824 272 192 136 96 70 50
1 1.049 547 387 273 193 141 100
1 1/4 1.380 1200 849 600 424 310 219
1 1/2 1.610 1860 1316 930 658 480 340
Yeah, I guess I was feeling verbose. Happens sometimes when I'm
procrastinating a little. :-)
I disagree about the fittings. The chart in the table above is still
based on equivalent length, so you need to include the fittings. And
the equivalent length for a 3/4" 90 degree bend is 2'. So if you use
4 of them to jog around an obstacle, you need to count those fittings
as 8 extra feet.
As for the method in the above PDF, it is a good method. It actually
addresses a different question: given the lengths and demands, how
should I choose the pipe sizes? Whereas the method I was using is
more appropriate for the OP's question: will a particular choice of
pipe sizes be adequate?
BTW, the sizing method in the PDF is quite conservative. In the
example given, it comes up with 1 1/4" pipe for the main branch. But
I'm sure that if you changed that to 1" and checked the pressure
drops, it would still be adequate.
So what you can do is use the PDF sizing method, and then once you
have a choice of pipe sizes, calculate all the pressure drops (which
will be per force OK), and then see how much "safety factor" you have
left at each outlet. Based on that you can try downsizing a few
branches and then recheck the pressure drops to verify they are still
yes, four elbows add to effective length but since the table steps are
10' at a time AND the delivered BTU's are conservative
Got a cite specifically for low pressure gas flow equivalent lengths?
Cutting the pipe size close (imo) is not worth the calc time, maybe as
an academic exercise (which I'm not adverse to)
but from a practical point of view the PDF is the way to go.
And the typical new install (usually what's being modified) doesn't
have that many elbows unless the installer was a hack.
Sometimes its just not worth the time to do a close calc when the
quick & dirty method will give you an adequate design, its not like
steel pipe is all that expensive.
And most people can follow the PDF method way easier than the calc's
I disagree with respect which method suits the OP.
It the OP checks his current piping system and proposed mods against
the PDF method & the "checks ok"....he's done.
If it doesn't check ok....then it's time to "sharpen" the pencil.
Plus it all depends on what is really the easiest way to physically do
From my first post, just google "natural gas 90 equivalent length".
The first hit should do it.
My original post was very long because as a mathematician I want to
explain why we are doing the calculations. Certainly it can be
reduced to using a chart like the PDF method. All you would need to
do is this:
Change the chart in the PDF to be pipe size versus flow rate, giving
the maximum allowed length. That's just presenting the same
information in a different way, you can still use the PDF method for
your initial design.
If you want to sharpen it, label each segment with the ratio of
"segment length/chart maximum allowed length". A solution is OK if
for each appliance, the sum of the ratios from the meter to the outlet
is less than 1. So if you see that somewhere the sum ends up quite a
bit less than 1, you can try downsizing an appropriate pipe segment,
update the segment ratios, and see if the sum is still less than 1.
Yes, your modification would allow very rapid & simple itteration
(which the current PDF does but not nearly as easily)
But Wayne, you'd be asking people to create ratios and add a few
Did you ever here the one about how an engineer, a physicist
and a mathematician each respond to a small house fire in the middle
of the night? :)
But the pressure may not drop. The gas meter is, among other things, a
regulator - it tries to keep the pressure constant.
In the instant case, the OP can experiment. Get a 1/2" garden hose and duct
tape it to both the source and target of the planned layout. Turn on
Does everything work?
Right, the regulator at the gas meter tries to keep the pressure
constant at its output. So if no gas is flowing, the pressure
throughout the system is a constant 7" w.c.
But whenever gas flows, the pressure drops as it travels, due to the
friction with the side of the pipe. So turn on all your range burners
and draw 60,000 BTUs/hr (60 CFH), and while the pressure will stay at
7" w.c. at the regulator output, 10 feet away down a 1/2" iron pipe,
the pressure will have dropped by 0.071" w.c. to 6.929" w.c.
And the system is to be designed so that the pressure at each outlet
is at least 6.5" w.c. So you need to size your pipes large enough to
ensure at most 0.5" w.c. pressure drop between the regulator and the
appliance shut off valve.
Thanks to everyone for the feedback. Clearly, installing a tee from the
existing 1/2-inch line has the potential to starve either the gas range or
water heater if both are operating. So, I'll extend the 1" supply line to
the point where both appliances can be individually attached. Much more
complicated but probably necessary.
Going back to the 1" supply line is the more robust solution for sure.
Then if you want a surefire solution that won't require any calcs, you
would need to run a 3/4" line to your gas range.
But if it that is alot of extra work, you can get an exact answer to
the question of "will teeing off the existing 1/2" line be OK?" What
you would need to provide is a diagram showing all your gas
distribution piping (and the new proposed 1/2" piping) like that in
the PDF Bob found:
The lengths given should include fittings based on their equivalent
lengths, but if it is difficult to tell you could estimate that part
using 2' for each 90 degree bend. Also, if your distribution piping
branches immediately after the meter, you can start diagramming after
that branch point.
With that information I can show you how to calculate the pressure
drops and answer your original question.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.