On Mon, 13 Dec 2010 17:49:00 -0500, firstname.lastname@example.org wrote:
There's some kind of misunderstanding here about simple fluid flow and
pressure, how gas burns, etc..
I can't get into technical details because I'm not an engineer.
But I know....things.
As I've mentioned, I cut down the flame on my old boiler by simply
moving the gas supply ball cock lever until the flame was where I
wanted it, and adjusted air flow to get a good flame.
That was a vertical flame - the burner was directly under the boiler
water jacket flue passages.
So there's no question a gas supply line ball cock - intended as a
stop valve - can regulate burner pressure effectively.
Understand that the gas company supplies natural gas to residential
customers in my area at 1/4 psi.
By reducing the volume allowed through the valve I reduced the
pressure at the burner orifices, and reduced the BTU per hour burn.
In that case I lowered exhaust temps, increased the on-cycle, and came
out ahead in terms of efficiency.
I wouldn't try that with my current furnace, because it has a
horizontal flames reaching into heat exchanger tubes.
The nozzles have a good 3-4" of open air between them and the heat
(BTW, that's a real good reason for an induced draft at startup.)
I strongly suspect gas pressure/nozzle size are critical for safe and
efficient operation on this one, and shouldn't be trifled with.
They were easily manipulated on my old boiler.
So what's this all mean?
If Home Guy plans on regulating gas burn on a new furnace, he should
at least find one with a vertical flame.
I don't know if they make them for forced air furnaces.
I guess we can argue if a partially-closed supply valve is acting as a
flow restrictor (reducing the quantity per unit time of gas that reaches
the furnace) or if it is functioning to reduce the pressure of the gas
reaching the furnace.
Obviously if the valve is partially closed, it must function primarily
to reduce the quantity flow to the furnace. It could very well be that
because of the size of the burner orifices that they are the real
bottle-neck to quantity flow, and the pressure on either side of the
partially-closed supply valve remains the same at all times.
I have been altering the size or intensity of two (2) furnaces over the
past 5 years by turning the variable control dial on the pressure
regulator inside these furnaces. This is the same control dial that
must be turned (and depressed) to the "Pilot" setting in order to ignite
the pilot light, and then turned about 90 degrees to another position to
allow full flow to the burners. But instead of turning this dial the
full 90 degrees, I turn it maybe 25 degrees to get a "lazy", less
A third furnace (which dates to about 1981) is a "whisper heat" unit
with electronic ignition (and a motorized combustion-air damper door and
resettable over-temperature sensors on various parts of the cabinet). I
had to re-solder the ignition transformer on the PC board control module
of that furnace 5 years ago (basically when it came under my care and
control) because I was observing intermittent ignition. That furnace
does not have a pressure control dial like that found in the furnaces
with a standing pilot. What I began doing this year is to regulate the
flame intensity of that furnace by partially closing it's gas supply
valve while observing the flames through the open damper door.
All 3 of these furnaces have long horizontally-placed burners that are
positioned at the bottom of the heat-exchanger galley where the flames
rise vertically directly from the burners.
I can only say that if you have access to an older-style furnace with
easily visible, horizontal burners (not the "in-shot" type) then you can
easily see for yourself how manipulating the main supply valve can
reliably and consistently alter the size or intensity of the burner's
Sure, you can "control" the flame, but accuracy and repeatability are
not really in your lexicon when you do this. Soldering the "jet" and
re-drilling it is a much more "scientific" , repeatable, and accurate
way of doing it. (and getting a jet of the same size/format as a
permanent replacement is even better)
It's not just the size of the jet either - the "format" of the jet -
the taper on the inlet side(if any) and or the outlet side, can
significantly affect the volume of gas flow through a jet of a given
Accuracy is not called for here.
Anyone dialing-down the gas supply to the burners will not know ahead of
time what the exact precise flow rate should be that they are intending
to achieve. Much the same way that you won't initially know what
setting your barbeque's controls or gas stove need to be in order to get
a certain temperature on the grill.
In this excercise, you dial the gas down, you let several hours (or
days) pass, you note how the duty cycle of your furnace has changed, and
you either leave it alone or you adjust it up or down as needed.
And also more effort for no real, effective gain in terms of the desired
If the furnace has a variable dial on it's gas valve/regulator, then use
it. If it doesn't, try the main shut-off valve.
Yes, you know that changing the jets by getting smaller ones (or making
them smaller with solder) will give you a smaller flame and less BTU's.
But you really don't know by how much until after they're in place. And
if the new jets are too small or not small enough, then you've got to
partially dis-assemble your burners and change the jets.
Makes about as much sense as saying that replacing the potentiometer in
my stereo's volume control with fixed resistors is a better way to
control the intensity of sound coming from my speakers. Does it matter
if the fixed resistor is "more accurate" ?
Your stereo doesn't need a specific fuel/air mix to operate the way it was
FWIW, I have *NEVER* seen a furnace gas valve with a "variable dial" on it.
Oh, and while I am at it, HomeBoy.... you sure that your name isn't really
Steve followed poor usenet message-construction style by unnecessarily
We already discussed adjusting the primary combustion-air baffle plates,
which are most likey already in the incorrect (lean) wide-open position
in your average open-burner, standing-pilot furnace anyways, making your
observation somewhat irrelavent, but still easily remedied.
Here ya go:
Now, do you want some help pulling your feet out of your mouth?
You are on drugs. See that blue dial? That's a variable-position
dial. You get more or less gas going to the burners depending on it's
position. Try it some time.
What is wrong with you people anyways?
You want to so hard to believe that it's not possible to dial-down the
BTU output of old furnaces.
I don't know what your problem is.
They make em steve. They have a sensor that goes in the supply air
and you set the valve according to the supply temp that you want.
Usually see them on direct fired make up air units. Seen them on
Reznor gas fired duct heaters too.
The King is dead but not forgotten.
Which is an extremely mickey mouse way of doing things. Changing the
orifice (jet) sise is the correct way if there is not an adjustable
pressure regulator in the system. The ball valve (or whatever) on the
1 inch iron pipe feeding the furnace is a pretty gross adjustment.
I wonder how much the cold air that is still flowing through the old
the air down in winter while it's moving through it 24/7? I would
air constantly in winter as I believe with losses through the ducts,
furnace, etc, its a
losing proposition. However, at least with a new furnace with draft
air moving throguh the combustion chamber when its off will be way
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