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Costs of heating water

Razer
Grafter
Posts: 1,375
Registered: 17-11-2012

Costs of heating water

How can I figure out if heating water is cheaper by gas boiler or electric immersion heater? I often hear people saying it is definitely cheaper with gas, but I don't really understand it because to my mind if you heat by immersion heater you are just using electricity. If you heat by gas boiler you are using both gas and electricity to heat the water.
Is it a matter of the amount of electric power required to heat water, as opposed to gas and the amount of electricity is takes to pump the gas heated water through the system to the tank?
38 REPLIES
Community Veteran
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Registered: 20-10-2012

Re: Costs of heating water

A combo gas boiler heats water on demand! No water storage present or required!
Geoff,
York.
Community Veteran
Posts: 6,735
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Registered: 02-02-2008

Re: Costs of heating water

You'd be surprised how little power is required to move things about compared to heating them up.
A typical central heating pump equates to a small light bulb in electricity consumption, when running.
itsme
Grafter
Posts: 5,924
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Registered: 07-04-2007

Re: Costs of heating water

That's why the government want Smart Meters fitted.
Steve
Seasoned Pro
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Registered: 13-07-2009

Re: Costs of heating water

Quote from: NedLudd
A combo gas boiler heats water on demand! No water storage present or required!
I have a combi, very economical.
Community Veteran
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Registered: 08-01-2008

Re: Costs of heating water

Source: http://www.energysavingtrust.org.uk/Energy-Saving-Trust/Our-calculations
Average UK price per kWh for gas is 4.64p, Average price per kWh for (Standard) electricity is 15.32p (3.3 times the price of gas).
Heating with gas is actually a bit less efficient but normally nowhere near enough to compensate for the price difference between the two fuels.
Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
Opinions expressed in forum posts are those of the poster, others may have different views.
nadger
Rising Star
Posts: 4,498
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Registered: 13-04-2007

Re: Costs of heating water

When we had new gas boiler fitted 17 months ago I was pleased it wasn't combi boiler and that we retained hot water tank and immersion heater.
When our previous boiler was condemned due to CO leak we were still able to get hot water.
Didn't notice a lot of difference in cost between heating water by gas boiler or electric.
kmilburn
Grafter
Posts: 902
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Registered: 30-07-2007

Re: Costs of heating water

There is one simple way to work it out.
You'll use roughly the same amount of energy to heat the water, 
Based on my current tarrif, electricity costs about 21p per KWh, while gas costs 8p per KWh.
It takes about 8KWh to heat 40 gallons (US) from 15 to 60 degrees.
I leave the rest of the exercise to the reader!  Wink
Community Veteran
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Registered: 02-02-2008

Re: Costs of heating water

Quote from: kmilburn
on my current tarrif, electricity costs about 21p per KWh, while gas costs 8p per KWh.

Good grief! Where are you?
My gas is 4.4p and electricity 12.5p per kWh.  Lips are sealed
kmilburn
Grafter
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Registered: 30-07-2007

Re: Costs of heating water

It's not as bad as it sounds, they're the tier 1 prices, tier 2 is a lot cheaper (no standing charge).
Community Veteran
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Registered: 21-03-2011

Re: Costs of heating water

If you boil a kettle water inside the house remember to deduct the cost of the reduced need to heat the building.  For example if it takes 1 unit to boil the kettle (1 KWh) using electricity it might use 15p of electricity, but you save on 1KWh of heating the building through the heat gained as the kettle cools (in the winter). In the summer when the heating is not switched on it is genuine lost energy.
Now Zen, but a +Net residue.
Community Veteran
Posts: 6,735
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Registered: 02-02-2008

Re: Costs of heating water

Similar logic applies to new-fangled light bulbs which, lets face it, are mostly used indoors in dark cold weather.
As a result I've largely reverted to bulbs that actually work as the savings seem to be "virtual" not real with low-energy ones.  Cry
Different logic for outside lighting and my most recent floodlight is indeed a 10W LED not a 100W linear halogen.  Cool
Community Veteran
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Registered: 08-01-2008

Re: Costs of heating water

10W floodlight...... wasteful!  Tongue
I recently replaced a 150W halogen with a 5.9W LED (covering a modest area at our front porch), the amount of light isn't that much less to be honest.
I don't mind paying for gas to offset the saving of indoor LEDs (I use 1.8 & 3W in many places though some are in 'multiple fitments').
If calculating the cost of heating water remember that a typical boiler is about 80% efficient* so add a bit to the cost per unit of gas, an immersion heater in an insulated tank can be taken as 100% efficient.
* An old boiler could be as low as 55 to 60% efficient, modern condensing boilers claim to be over 90% efficient but most do not achieve this rating when heating water to usable temperatures, so gas is usually significantly cheaper as a heating source (economy 7 overnight can be OK compared with an old gas boiler and oil/LPG is rather expensive so not always worthwhile).
Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
Opinions expressed in forum posts are those of the poster, others may have different views.
Razer
Grafter
Posts: 1,375
Registered: 17-11-2012

Re: Costs of heating water

Quote from: NedLudd
A combo gas boiler heats water on demand! No water storage present or required!

I wish I had a combi boiler; I much prefer them.
Quote from: HPsauce
You'd be surprised how little power is required to move things about compared to heating them up.
A typical central heating pump equates to a small light bulb in electricity consumption, when running.

Oh right. So I don't really need to worry about 'added electricty cost' when heating with gas. Thanks for that.
Quote from: kmilburn
You'll use roughly the same amount of energy to heat the water, 
Based on my current tarrif, electricity costs about 21p per KWh, while gas costs 8p per KWh.
It takes about 8KWh to heat 40 gallons (US) from 15 to 60 degrees.

So the energy loss (and excess cost to pump) whilst the heated water travels the pipes would be negligible and thus still make gas cheaper? I just wonder if that is factored into this idea that it takes roughly the same amount of energy either way.
Community Veteran
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Registered: 08-01-2008

Re: Costs of heating water

Yes, same energy (less inefficiencies) but gas is a lot cheaper per unit of energy.
Simples!  Smiley
Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
Opinions expressed in forum posts are those of the poster, others may have different views.