Gas vs. Electic: Energy budget heating 3 cups of water ...

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Offline elecht

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I have a question I THOUGH would be easy to answer, yet the more I dug, the more confused I got. The complications arouse in the usual places; conversions and standardizations.

The question:
What's cheaper to do:  heat 3 cups of water in a typical kettle on a typical kitchen gas stove, or heat the water in an electric kettle? And by how much? What is the approximate cost of each's process?

Some empirical particulars:
--stove kettle is typical half-dome style steel kettle, 8 inches across the base. Not particularly flimsy, just a typical thin-gauge steel, maybe a shade thicker gauge on the base.
--gas source is a typical gas range burner (GE range).
--from user manuals I've seen on the web, and experience w/ other ranges, the burner's output LOOKS TO BE  6000 BTU rating. This is just a guess..... Some ratings I've seen are 5,500 BTU, to 16,00 BTU/burner. This burner seems to be on the less powerful (?) side ....
--Altitude is 7K feet (Evergreen, CO)
--true natural gas, not propane.
--XCel energy rates on natural gas: $0.07 per therm (Th). I understand this to be 7 cents/100 ft gas?
--it takes precisely 9 minutes to heat the 3 cups water in the kettle.
--it is evident a large portion of the HEAT escapes. The heat goes around the kettle, escaping into the air.

Contrasts to an electric kettle:
1000w-rated kettle, taller than wide, not too flimsy metal, a bit thicker than the kettle.
--takes 1.5 minutes to heat the 3 cups of water.
--XCel energy residential rates electricity: $0.033 /kWh.

REASON: I'm hazarding its #1) cheaper to heat w/ an electric kettle, and #2) more energy efficient. --And I believe its more efficient by an order of magnitude.
I'm not necessarily assuming its CHEAPER by an order of magnitude, but is more efficient to heat via the electric kettle by far.

ADDED COMPLICATOR: secondarily, factor in the complete power-budget if we consider the energy cost of generating the electricity and delivering it TO the outlet the kettle is plugged into. This MUST skew the analysis, yet I'm thinking the heat-loss incurred by the gas burner is great, and hence the least effective way to heat this water, and by a LOT.

I am grateful for how to frame the math, and then what the return would be, and then framing the answer in a meaningful, plain-english fashin.

Thanks much! Will settle a typical disagreement re: domestic energy usage.


E. Lecht


Offline techmind

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Gas vs. Electic: Energy budget heating 3 cups of water ...
« Reply #1 on: 08/12/2007 22:12:57 »
I answered this question on a webpage some months back:

In my example I did not have a lid on my saucepan, which would reduce the efficiency of that method slightly.

My conclusions were that an electric hob is a very bad way to heat water.
In terms of either cost or CO2 emissions, an electric kettle is pretty good, and a gas hob is not far behind. The difference is that with the gas hob you get more heat in the room as a by-product. If it's cold in the winter, this is probably a welcome side-effect. If you're too hot in the summer (or worse yet, running air-con) then you probably want the least additional heat in the room.

The web page also gives links to sources for CO2 etc for different energy sources.

In the UK, electricity costs something like 11p/kWh and gas 3.2p/kWh (depending on your supplier and tarriff).
« Last Edit: 08/12/2007 22:16:42 by techmind »
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Offline Pumblechook

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Gas vs. Electic: Energy budget heating 3 cups of water ...
« Reply #2 on: 08/12/2007 22:14:48 »
Elec here is 10 pence per kWh.  Gas is 2.5p per kWh..  1/4 of the price so gas should be cheaper but maybe there is more heat loss with gas so that will narrow the gap.


Offline Bored chemist

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Gas vs. Electic: Energy budget heating 3 cups of water ...
« Reply #3 on: 09/12/2007 13:13:07 »
To do this properly you also need to say if its Summer or Winter.
If it's Winter then the "waste" heat going into the room is useful- it means the thermostat on the room heater cuts out a bit more and so saves power.
If it's Summer then (in some houses at least) the air conditioning has to work harder to remove the extra heat.
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