This morning it was a little cold, so I turned the heat on while I was
in the shower. This uses natural gas. Our house is not large, maybe
1200 sq feet or so.
Is it true that in terms of actually turning on natural gas, there is
a surge of therms (of perhaps even kw to get it going) that is fairly
costly? This was his point. Also, my point was that it was only for
10 or 15 minutes, so it couldn't be too costly. What's the maximum
that it could cost would you say?
Just curious about how this works...
Why not get an exact answer by reading the meter before and after?
Yes there will be a far greater cost in running the system from cold for
15 mins, compared to running the system for the same period once the
place is warm.
The worst case would be the heating system running at full rated
capability for the whole 10 or 15 mins.
eg, if your heating system is rated at 16kW and each kWHr costs 10p -
then your using the heating for 15 mins will add 40p to the bill, at most.
Here is a typical boiler:
Buderus 600/19R Boiler
See that it is rated at 19kW.
That means that, if it is running continuously for 1 hour, it will use
19kWHr of *gas* during that hour.
Now, in practice, most boilers don't run continuously because, once they
have heated up to the set point, they stop heating until the temperature
falls. This boiler will use 1kWHr of *gas* about every 3 minutes when it
is heating a house/flat from cold. Once the place is warm, that
consumption will fall and, hopefully, fall a great deal.
So yes, it could easily use several kWHr of *gas* to "get going". But
the most it will use is about 1kWHr every 3 minutes. So 12 minutes of
heating from cold is going to cost 4kWHr on the *gas* bill, at most.
You seem to be interpreting Sues' post in a unique way: Most gas furnace
systems use forced air which requires an electric blower. Others use heated
hot water which use an electric pump. The only "surge to get it going" on a
modern system is a tiny spark to light the flame plus a very brief
electrical "surge" to start the blower.
Personally I'd find a roomate that likes it warmer and split the utility
My emphasis was on the flatmate's concerns - the effect of running the
central heating for 10-15 mins in the morning on the utilities bills.
The effect on the electric bill is going to be miniscule. The effect on
the gas bill is going to be under a tenner a month.
The comprehension gap is possibly that the OP equates kW to electricity
and I should maybe have written in terms of therms instead, to avoid
confusion. However, it is now the year of the FruitBat - and kWHr is now
used instead of therms for gas, in the UK at least..
Your roomie is simply wrong. This is a myth that bringing up a body to
temp once a day costs more than keeping it hot all day. Gas only has 2
states, on and off. The only way this could be true is if you could
keep the house hot all day long by running less than 15 minutes a day.
Another way to look at this is to analyse heat loss to the outside.
The most heat is lost when the difference between inside and outside
is the greatest. If you don't keep the house hot all day (and night)
you are not losing heat all day and night. This is mostly affected by
how well your house is insulated
So how is the roomie wrong? The roomie is saying *not* to turn the
heating on in the morning for that 15 mins. The roomie is not saying
leave the heating on all day instead..
By putting the heating on in the morning, most of the heat energy
injected by that 15 mins of use is lost during the day (when,
presumably, the house is empty with everyone at work).
The roomie is right in saying that putting the heating on for 15 mins in
the morning costs a disproportionate amount of cash. It would be cheaper
to manage without and just put the heating on in the evening, when the
house is occupied.
Because it is not a surge. The same amout of gas
is consumed per unit time, regardless. When it's
off, it's 0 cu. ft. per unit time; when it's on,
it's X cu. ft. per unit time. There is no pronounced
spike in gas consumption at turn on vs steady state on,
comparable, for example, to a light bulb or motor start
up vs steady state on.
Bottom line, the more time the heater is running, the
more it costs, but the added cost is not related to surge.
The roomie is saying *not* to turn the
You cannot expect a non-engineer to use the correct words. What the
roomie is concerned about is the effect on the utility bill of running
the central heating for a few minutes from cold. He's called it "a
surge" - an engineer would call it "a few minutes of sustained full power".
There will be a spike in gas consumption. Without turning the central
heating on - the gas consumption of the appliance will be effectively
zero from the previous evening when it went off to the next evening when
it comes on. Turning it on and off during that period would indeed show
a "spike" in demand - as consumption would almost instantly rise (to the
full power demand) and shortly after fall again (as the heating was
switched back off). But that is irrelevant - all that the OP and the
roomie is concerned about is the cost of running the central heating for
a few minutes from cold, each day. I've suggested two ways of working
that out: reading the meter before and after and estimating the worst
case by taking the product of the kW rating of the boiler and the cost
of gas per KWHr and the fraction of an hour it is run for.
Engineers must always allow for the mis-use of engineering terms by
non-engineers and try to understand what they intend... and identify and
address their real concerns.
Except that a natural gas fired furnace doesn't use more or less power
or gas after it has been "warmed up". They ignite, the heat exchanger
gets hot, and the blower blows the heated air in the house side of the
heat exchanger into the house being heated. The air exiting the furnace
ducts is that same temp within a mere few minutes of turn on as it would
be after running for hours.
No, there will not. On is ON, and OFF is OFF. The heat exchanger that
gets heated by the ignited gas flame has ONE SINGLE setting for the flame
height. That setting is factory (or field) optimized, and does not vary
because of some imagined state that the furnace is in.
15 minutes of gas furnace heat is 15 minutes of gas furnace heat, no
matter how you wish to slice it up. The heat exchanger, and the ducts
are "settled in" within a few minutes of start-up, and that happens even
when the furnace is left on all day, as it cycles, by thermostat
completely on, and completely off.
Bullshit. Not using it is zero consumption. Any kid would know that.
Using it has a specific, set rate of consumption, and it doesn't matter
if it is ten below out or 65 degrees. The furnace doesn't change a thing
about its behavior.
Are you sure that you know how a gas furnace operates?
Even if the system is ON ALL DAY, the furnace starts from "cold" every
time it runs. It is a CYCLIC device! If it was on for 35 minutes
getting the house to the set point, and off for an hour, the ducts have
cooled back to ambient within ten minutes of the thing CYCLING off.
There is no boiler.
It called spelling it out. Consider that as having been what I just
did for you.
The "roomie" is right that using it does cost more than not using it,
but 100% wrong in stating that using it at one time of day costs more
than using it at another time of day.
Besides.. gas is cheap.
Thanks, that helped a lot.
I am in the UK - where domestic heating systems are almost invariably
hot water ones. The system has a central boiler which has to heat a
large volume of water in the system up to temperature and circulate that
hot water to radiators in the rooms, to warm them. There is a large
amount of initial energy consumption that is involved in doing so,
because there is a large mass of water that has to be heated.
You appear to be in the US - where domestic heating systems, from your
post, seem to rely on heating air in a furnace and blowing that hot air
via ducting into the rooms. The system presumably responds very quickly
and doesn't store large amounts of energy in the transfer medium.
In the hot water system - running the system for a few minutes from cold
in the morning and then switching it off uses a large amount of power,
which is left in slowly cooling water - presumably in an empty house, in
In a hot air system - there is no large mass of water to heat. So there
will be no significant energy left stored in the system, once it is
turned off. There isn't that heated mass left to slowly cool.
Hence, the misunderstanding. I had quite forgotten that you heat houses
rather differently in the US.
So this rather does depend on whether the OP has a heated water central
heating system - or a ducted hot air system..
My apologies - I forget that the USA often has strange ways of doing
Strange? We stopped using steam and radiators five decades ago.
Reason? Efficiency, and operating cost of boilers, maintenance costs,
failure mode prone operation (leaks, etc.). Safety (boilers explode
Who is strange?
When Sue said water she meant water!
Boiler thermostats, not room thermostats, are normally set around 140 deg
F as this gives maximum efficency with little risk if someone touches a
hot pipe or radiator.
Maintainance really comes down to ensuring the burner is working properly
and I cannot see that this cost would be any different between hot air or
hot water systems. We have just had our boiler serviced and it ammounts to
a good clean out, check operation of flame failure and other safety
devices, thermostats and combustion efficency - including checking for
things like CO emmisions
Modern condensing boilers are around 90% efficient.
From is valid but subject to change without notice if it gets spammed.
So what? Hot water systems are still fed by a STEAM boiler.
The efficiency of the boiler has nothing to do with the efficiency of
the distribution system.
A single radiating source in a room heats the air that happens to
convect near it. A ducted hot air heating system adds heated air to a
room, which is much more efficient.
The cost of operation of a forced air heating system is well known to
be far less than that of a hot water based system. Particularly if said
hot water system uses 70 year old radiator technology. There are hot
water systems in use that use much more efficient radiator elements that
span a baseboard, etc.
The point is that a single radiator in a room uses a small amount of IR
energy to heat the air that is in close proximity to the radiator. A
forced air system uses a HUGE amount of IR energy to heat the air passing
over a heat exchanger, which then gets pumped into the rooms already
It is well known that the forced air systems are more efficient at this
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