[Shop-talk] Natural Gas vs Propane Grills

[David Scheidt]

On Sat, Apr 2, 2011 at 6:12 PM, Randall <TR3driver at ca.rr.com> wrote:
>> Does the
>> last two feet
>> limit all that came before it?
>
> Don't forget, the area of the pipe is proportional to the square of the
> diameter. B So your 1/4 pipe has only 1/4 the cross-sectional area of the
> 1/2" pipe. B Think of putting your thumb over the end of a hose.
>
> Just for chuckles, I found an on-line calculator and put some numbers into
> it. B At 1 cfm (about 60,000 Btu/h), the drop through 2 ft of 1/4" pipe is
> more than the pressure at the regulator.
>
> IMO even the 16 feet of 1/2" is reducing the output at least a little bit,
> depending somewhat on how big the burner is.
>

If it's really 18 feet to the regulator, and it's not a twisty run,
20' of 1/2" type K copper pipe can supply 52K btu/hr, which may or may
not enough to run the grill.  (It should have a requirement in the
manual.)  If it's a twisty run, the typical derating is to increase
the length of the run by 50%, which drops the capacity to about 42K
btu/hr, which is probably too low.  That's with a drop   of 0.5 inches
of water, which is the standard design drop (it's code some places,
just recommended practice others).  If it's longer than the 18' to the
regulator, 1/2" is clearly not big enough.  Then he'd need to increase
the pipe size, or got to psi system, with at appliance regulators, at
least branch regulators; he'd need a gas plumber to tell what's
reasonable for his situation.  Or give up on gas and buy propane.
Running a gas line buys a bunch of propane tanks.

--
David Scheidt
dmscheidt at gmail.com