I heard that adjusting the gas valve on my standard natural gas furnace will
make it more efficient.
By partially closing the gas valve reduces the flame. Although the furnace
would run longer, the flue temp is reduced meaning lower heat loss and
improvement in efficiency.
An analogy is like driving a car the same distance once fast and once slow.
When driving slower, it obviously will take longer, the engine is on longer,
yet fuel usage is less.
I have no way to verify if this is BS or not.
On Fri, 12 Sep 2008 05:21:16 -0700 (PDT), Mikepier
Last winter I lowered my thermostat everytime they told me to do so on
tv. I saved about $850 on my gas bill. However, my wife and two of
our children died from from freezing to death. Myself and my one
surviving child ran up $235,000.00 in medical and hospital bills after
we were hauled away by an ambulance. I am now permanently disabled
since they had to remove both my legs which had frozen, and my son
will never be able to reproduce, or use his fingerless hands as a
result of the cold.
When you "lowered" it, how far each time ?? 1 inch, 1 foot ?? Did
you not re-connect the wires ?? Did it get down to the floor ??
Sorry about your family. Were you able to find a nice nursing home
that accepted Medicaid ??
Yup and while not a 'gas man' turning it down might risk the furnace
not coming on when it should. And why would running the furnace slower
save fuel anyway?
Just suppose you were to run hot water into a pail on a cool day.
Inevitably the pail would lose a little bit of heat while you were
filling it; maybe taking a minute or so to fill the pail with hot
Then suppose you were to set the tap to very low or even just a drip
of hot water every second or so?
At the end of maybe an hour the pail might be partially filled and the
water would have lost it's heat anyway.
After all it's heat you are trying to make, to heat the house!
A certain amount of gas or oil or wood etc. can be burned to make a
certain amount heat (depending on the efficiency of the furnace etc.)
hard to see that fiddling around with the gas/oil supply would make
the furnace any more efficient. In fact maybe make it unsafe!
It also used to be said that for a furnace/heating system to be most
effective it should be just big enough and be adjusted so that it runs
almost continuously (i.e. at highest efficiency cos it's not cycling
and cutting in and out heating up and cooling down as often), during
the coldest weather.
Don't think the car analogy is good one.
my best friend throttled his back last winter, and had no troubles.
wouldnt recommend this for a direct vent 90+ type.
his furnace would occasionally gop boom on start up, throttled back it
didnt but ran longer.
he cleaned the burners this summer they were clogged near pilot light,
no more boom explosions
Your friend doesn't have a furnace company do the annual maintenance on his
furnace. He thinks he's competent to tell you that "no problems" after
Please take out a life insurance policy on his family, and put me as the
well he has multiple engineering degrees, and his best friend has a
PHD in mechanical engineering
interestingly he had a service company out who just said replace
furnace. while another friend a retired HVAC instructor said clean
my buddy doesnt believe a new furnace will save him money. I replaced
our furnace by spring the proof will be in equitable gas bills:)
Incidently my buddy who cleaned his furnace converted both his
vehicles to compressed natural gas in the 70s and they still run on it
not only did he design and build the system his machine shop and
foundry produced nearly all the parts.......
he is a retired teacher.....his effective price per gallon is about 2
bucks, natural gas has nerarly doiubled in cost in the last 2 years:
But your friend likely understands what he is doing and the various
reasons why it may or may not be a good idea for someone else since he
can babysit the project and observe the results.
You might want to point your buddy in the direction of flame modulation.
Simply lowering the burner output is very simplistic and may or may
not work depending on how well matched the burner output is to the
highest heat loss.
On Fri, 12 Sep 2008 08:54:09 -0700 (PDT), " email@example.com"
Ok, Hallerb, you ding dong. Listen up before you kill someone.
You, your ideas and your nutty Engineer crap is so full of holes it
isnt funny. This is a real simple checkout if you dont believe it.
A furnace is designed to operate within a certain range. Next time you
can, get your hands on a combustion efficiency analyzer. Put it in the
flue. On a 90% furnace just put it in the outlet pvc pipe. On a
standard furnace, just stick the probe in the metal flue. Now, start
cranking the gas pressure down and watch the CO reading (thats carbon
monoxide) go off the chart. Just for giggles, you can even turn the
gas pressure way up and get the same effect. In short, the burner was
designed to burn properly within a certain range. SO, if you are
truley bent on killing people, just keep popping off with your silly
Oh really, there is a maximum stated temp the exchanger is designed
for and cutting gas to be within the range is normal to do. How is his
idea unsafe, how can he kill anyone, I guess down south yur ways you
exhaust into the basement because chimneys are too expensive. Running
at the low end of the exchangers temp is how I set mine up since my
hack pro was to lazy to check it. So are burners different on
Modulating gas valves, no, its just less gas. The idea has merit to
check what your temp is to be sure it is within the specified range,
and within the "range" is fine.
On Fri, 12 Sep 2008 12:01:17 +0000, JohnR66 wrote:
Gee, unless the source of this information is an Engineer, and a H & C
mechanical engineer at that, I would treat that wild donkey guess with a
grain of salt.
Reducing Flue temp will not make your furnace more efficient. Improved
design of the heat exchanger will. Aside: your furnace's gas burners are
inside a 'firebox' which keeps the carbon gas in the flue and not in the
house. The firebox has the house air blown around the outside which
picks up the heat. The better the design of the heat transfer from the
firebox to the air, the more efficient the furnace will be in heating
your home. Heat transfer also has to do with the velocity of the air,
the metal used (better transfer metal will not last as long), and of
course the temperature inside the firebox. ( I may have forgotten
Replacing the pilot light with an electric gas flame starter (like
propane outdoor grills have) will also save money.
BS. To make a gas furnace more efficient you must either get more BTU's
out of a fixed amount of gas or improve the heat transfer from the flame to
the house. More efficient furnaces have lower flue temps not because of
lower flame temps, but because more heat is transferred to the house. To
measure efficiency compare the flue temp to the duct temp.
Simply lowering the flue temp will also lower the duct temp.
It could help if ducts are restrictive and exchanger temp is to high,
mine was and I cut down on the gas shutoff valve to lower exchanger
temp to within spec. Test the temp above the exchanger and find out
what is specified and lower it to the low end of the design temp. To
high a temp also lowers exchanger life by many years.
Once you've got that figured out move on to your car---must be a way to
reduce the gas flow so that the car will run slower no matter how hard you
step on the gas pedal. You'll get where you're going, will take longer and
you will save on fuel. At least, if done right, (like putting a wooden
block under the gas pedal) the engine won't blow up---can't say the same
for your furnace.
Lower flue temp is how high efficiency furnaces get their efficiency. Some
ammount of temperature is needed. On the older furnaces to create the
thermal lift to get the flue gasses out of the house. In moderately newer
ones, to keep the flue gasses from condensing in the chimney. The newest
furnaces with PVC vents, the flue gasses are cold already.
I predict that if you turn down the gas, y ou'll have other problems which
will more than use up your fuel savings.
Using your car analogy. You save 14% of the gasoline bill. However, by
driving slowly, the exhaust doesn't blow the noxious chemicals out of the
tail pipe. The corrosive combusion products eat up your exhaust system, and
you have to replace all the pipes. Further, the carbon monoxide isn't blown
out of the car. Your family develops flu like symptoms, and turns cherry
red. You are home from work for a week with killer head aches and two of
your children die from monoxide.
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.