Water Heating Question

HobbyMan

Just wondering which is cheaper for heating water for a shave;

The immersion for two minutes or the boiler for a half hour?

It's a bone of contention between myself and the Mrs (I favour the immersion). :rolleyes:

scudo2

1th rule of marrage ,
The wife is always right.
Even when she's wrong.





It's 50/50 in your scenario, in my opinion.

ted1

HobbyMan wrote: »

Just wondering which is cheaper for heating water for a shave;

The immersion for two minutes or the boiler for a half hour?

It's a bone of contention between myself and the Mrs (I favour the immersion). :rolleyes:

With the boiler can you isolate the cylinder or do the rads come on? A kwh of gas is about 1/3 the price of electricity. A gas boiler is 85-90% efficent, electricity is 100%. Providing yiur heating the same amount if water then gas wins hands down. However there's losses as you need to heat the water between the cylinder and boiler. So it all depends on the particular house. I use an electric shaver no need for hot water

jeepers101

Come on people. He's more than likely just using the sink element when using rhe immersion. Immersion for two minutes would be way cheaper.

2011

jeepers101 wrote: »

Come on people. He's more than likely just using the sink element when using rhe immersion. Immersion for two minutes would be way cheaper.

Unlikely.
But it depends on many factors, the main one being how much extra water each system has to heat in order to provide water hot enough to shave.

There are gas boilers that fire up when the hot tap is turned on, these units heat DHW as it flows through the boiler and then shut off when the tap is closed. These would be far more cost effective than an immersion.

HobbyMan

Thanks for the replies guys.

I do isolate the immersion and use the sink element. Currently the rads turned off when the boiler goes on for hot water when we need it.

I will continue to use the immersion as it is so much faster.

Looks like the problem will be solved soon anyway. We had a lovely summer. :-)

Edit: 2011 I just have a regular boiler. Nothing as fancy as the one you described.

danjo-xx

or maybe keep a flask of hot water in the bathroom before you go to bed:)

dingding

http://www.willis-renewables.com/immersion-how-it-works.htm

I have one of these and I can recommend it. Does about a litre of water per minute.

And I control it with a Climote.

2011

.....or you could just use an electric kettle. It's quick and you can heat exactly the right amount

Cerco

Buy an electric razor or grow a beard. You will save on water charges as well as electricity.

shane 007

For that low volume of water, the immersion will be far cheaper to heat it than the gas boiler. The gas boiler will always overshoot the demand requirements. Even a cylinder coil cannot take the full power of a boiler as standard coils are usually sized at 1kw per 50 litres of cylinder volume & about 2kw per 50 litres for rapid recovery coils.

Even if the boiler is a high efficiency boiler, it will fire on full power until the return temperature heats up before it goes into modulation mode.

Costs, for example:
20kw gas boiler = approx 6.5 cent per kwh
20 x 6.5 cent = €1.30 per hour
So 30 minutes = approx €0.65

Immersion 18 cent per kwh
3kw x 18 cent = €0.54 per hour
You say it only takes 2 minutes to get the amount of hot water you require, so based on 2 minutes:
€0.58 / 30 = €0.02.

So the immersion for that volume of water being heated wins hands down & it would save you carrying the kettle upstairs

John T Carroll

HobbyMan wrote: »

Just wondering which is cheaper for heating water for a shave;

The immersion for two minutes or the boiler for a half hour?

It's a bone of contention between myself and the Mrs (I favour the immersion). :rolleyes:

"The immersion for two minutes", assuming a 3 KW Immersion heating say 50 Litres of water then the temperature rise after 2 minutes would be less than 2 Deg.C. (3X(2/60)*860/50) = 1.72 Deg.C. How are going to get a hot shave out of this? or have I too much drink taken yet again!. Try the kettle as suggested, below.

HobbyMan

John T Carroll wrote: »

"The immersion for two minutes", assuming a 3 KW Immersion heating say 50 Litres of water then the temperature rise after 2 minutes would be less than 2 Deg.C. (3X(2/60)*860/50) = 1.72 Deg.C. How are going to get a hot shave out of this? or have I too much drink taken yet again!. Try the kettle as suggested, below.

It's probably somewhere between 5 - 10 minutes in all honesty. It's a very short time anyway.

I just flick the switch, clean up a little and viola, I have warm water.

It's much faster than the boiler although I should time them both exactly and use the maths above to figure out the costs.

Anyway we are not that hard pressed for cash. The main point is that I favour the immersion and the wife says that I should use the boiler.

RebelButtMunch

John T Carroll wrote: »

"The immersion for two minutes", assuming a 3 KW Immersion heating say 50 Litres of water then the temperature rise after 2 minutes would be less than 2 Deg.C. (3X(2/60)*860/50) = 1.72 Deg.C. How are going to get a hot shave out of this? or have I too much drink taken yet again!. Try the kettle as suggested, below.

Good calculations, but the element isn't heating 50 litres of water in one go. It's heating only the water that's in direct contact with it. This hot water then convects to the top of the tank, where the water exits. So, maybe it could heat just enough water to fill the first two or three inches of the tank, which might be enough for a shave. caveat: Thats all just guess work.

shane 007

If you wish to get an accurate cost on the boiler side, take a meter reading (m3) & remember the last 3 digits in red are 1,000's of a m3 so reading would be something like 24373.025m3. Switch on boiler, do not turn on any other gas appliances, heat water. Switch off boiler & take a second meter reading.
Subtract 1st reading from the 2nd reading & multiply the result by 10.8.
Multiply this figure by €0.065 & this will give you an accurate costing for the gas side.

Do the same for the immersion but just time it accurately, 3kw immersion x €0.18 for one hour. Divide that by the minutes, etc.

For small volumes of water, you will find that the immersion is much cheaper due to efficiency & not having an over-supply of kwh. The cylinder water takes 100% of the heat generated from the immersion. The gas boiler will produce 20kwh but looses 10 - 20% due to pipework losses & the coil cannot take much more than 3 - 6 kwh.
For larger volumes, the gas will be much cheaper, so for showers, baths, etc. the gas will be much cheaper to heat the whole of the cylinder.

John T Carroll

RebelButtMunch wrote: »

Good calculations, but the element isn't heating 50 litres of water in one go. It's heating only the water that's in direct contact with it. This hot water then convects to the top of the tank, where the water exits. So, maybe it could heat just enough water to fill the first two or three inches of the tank, which might be enough for a shave. caveat: Thats all just guess work.

Thats quite true but I dont think one would see much stratification after 2 minutes of heating. Now, 10 minutes heating would certainly give a nice bit of "top heating" and I'd say would be fine for a shave/wash. Theoretically, using a 3 KW immersion for 10 minutes would heat 14 Litrs of water from 10C to 40C...[3X(10/60)X860/(40-10)] = 14.3 Ltrs. The cost of this @ 18c/Kwh is3X10/60*18 = 9 cents (excellent value for money). Compare this with spending that same 9 cents on Kerosene, kero was approx 85c/litre when I last bought it, so 85c/litre is about 8.1 cent/kwh, (85/10.5). 9 cents worth is 1.1 kwh input to the oil fired boiler, a "70/90" Boiler would have a firing input of about 2.6 LPH or say 27 kw/hr so your 9 cents worth would give a firing time of 2.5 minutes (1.1/27)X60 = 2.44 minutes.(Gas firing would give about 3 minutes ) Two or three minutes firing in an oil or gas fired boiler would hardly heatup the metalwork not mind any water.....the immersion wins hands down!. We wont mention that kettle any more but a cup of tea would be nice while having a shave.

I have a top mounted immersion which heats 25/30 litres of water, the cylinder has a very accurate PT1000 temperature probe mounted in the top of the cylinder, I will monitor this shortly and see what the temperature gradiant is.

2011

It still comes back to post #5:

But it depends on many factors, the main one being how much extra water each system has to heat in order to provide water hot enough to shave.

John T Carroll

Yes, it certainly does.

Unfortunately I couldnt monitor the cylinder temperature gradient as my hot water cylinder top stat pocket is located just below the bottom of the 11 ins immersion element but I can certainly vouch that there is hot water available at about 35C/40C after 10 minutes, I didnt install an electric shower until about 7 years ago as it wasnt until then that I was happy to trust a RCD (RCBO in my case) to give me accectable protection. In the summer time, I used to switch the immersion on for 10 minutes (with a mechanical delay off timer) and I could have a very comfortable 3 to 4 minute shower each morning with little or no cold water dilution, that immersion is still going strong after 42 years.