# is roommate right about the cost of turning heat (gas) on briefly in the morning?

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...
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Zarlot wrote:

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.
--
Sue

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I see ... so natural gas does use Kw to get going...never knew that..
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Zarlot wrote:

Here is a typical boiler:
http://www.discountedheating.co.uk/shop/acatalog/Buderus_Regular_Boilers.html 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.
-- Sue
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wrote:

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 costs.<g>
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Tim Perry wrote:

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..
--

Sue

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I cant find this on my Chinese calendar:)
and kWHr is now

what's next? Gasoline (petrol) sold by the kilowatt-hour?
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Tim Perry wrote:

Car engines have been rated in kW instead of bhp, for some time.
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Sue

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Pulls up to the pump in a 200kw SUV and charges a tank of liquid electricity on his electron express card and complains about the BTU tax.
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746w = 1 horsepower - so do the sums.
but my gas bill has been charge in kW for many years.
--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11
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Who knows

Indeedy
--
Stuart Winsor

From is valid but subject to change without notice if it gets spammed.
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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
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snipped-for-privacy@aol.com wrote:

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.
--
Sue

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Palindrome wrote:

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.
Ed
The roomie is saying *not* to turn the

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ehsjr wrote:

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.

--
Sue

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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.
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ChairmanOfTheBored wrote:

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 many cases.
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 things..
--
Sue

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Reason? Efficiency, and operating cost of boilers, maintenance costs, failure mode prone operation (leaks, etc.). Safety (boilers explode rather violently).
Who is strange?
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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.
--
Stuart Winsor

From is valid but subject to change without notice if it gets spammed.
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wrote:

So what? Hot water systems are still fed by a STEAM boiler.

Irrelevant.

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 heated.
It is well known that the forced air systems are more efficient at this task.
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