Estimate of cost to heat the water for a bowl of washing up.

tomstickland

That's not the costs to heat the entire tank from cold. Just the cost to cover the lost heat and heating the small amount of water that is used each day.

Cardew

I think Tom's figures seem quite reasonable - and his logic as usual faultless.

The accepted wisdom is that the average household uses 3,000kWh pa to heat hot water and Tom's figures would indicate that about 900kWh pa is heat loss*

A couple of comments:

* Firstly 'heat loss' is something of a misnomer as the 'lost' heat warms up the house much like any other 'radiator'.

I suspect the 'heat loss' will be less for a family who have their HW on a timer and use more water during the day.

900kWh costs me about £20 for gas. Frankly £20 a year for the convenience of having constant hot water available is a bargain - especially as much of that £20 goes toward warming my house.

Incidentally that £20 is perhaps a fair indication of the saving a Combi boiler will have over a conventional HW tank system.

tomstickland

Yes, heat loss being specific to the water system, so the hot water tank is essentially another night storage heater.

susan1

heavens to murgatroyd, is it really worth it or is it why i am always broke. i just shove it all in the dishwasher. i do try and boil water in the kettle just sufficient for my needs at the time. havn't quite got round to putting the remainder in a flask:D

mech_2

susan1 wrote: »

heavens to murgatroyd, is it really worth it or is it why i am always broke. i just shove it all in the dishwasher. i do try and boil water in the kettle just sufficient for my needs at the time. havn't quite got round to putting the remainder in a flask:D

I wouldn't worry. Modern dishwashers use an amazingly small amount of water and hence I assume they're also pretty energy efficient.


This is a great thread :T (or maybe that's just OCD speaking).

cm233lh

tomstickland wrote: »

I've just bought an energy meter from Amazon and plugged it into my kettle.
A brimmed kettle of water (about 8 cups) uses 0.16 units (Kilowatt hours, aka Kwh).

Incidentally, that should be kWh, not Kwh.

k (lower case) is the prefix for 1000
W is symbol for Watt (upper case as it's named after a person)
h is symbol for hour (lower case as it's not named after a person.

Sorry to be pedantic, but these are international symbols and if you use them incorrectly then you risk being misunderstood.

(same with KJ by the way - should be kJ (J for Joule named after a person).

mute_posting

cm233lh wrote: »

Incidentally, that should be kWh, not Kwh.

k (lower case) is the prefix for 1000
W is symbol for Watt (upper case as it's named after a person)
h is symbol for hour (lower case as it's not named after a person.

Sorry to be pedantic, but these are international symbols and if you use them incorrectly then you risk being misunderstood.

(same with KJ by the way - should be kJ (J for Joule named after a person).

<rant>
I don't think anyone on this discussion was likely to get mixed up, really (given the context the units were being used in)...

AFAIK there is no "K" prefix, so it is unlikely to make any difference (to people's understanding) if OP writes "k" or "K". Likewise with the Watt unit - AFAIK there is no unit denoted by a lower case "w".

As for the "h", should that be miss-typed in upper-case, is there such a thing as a Watt-Henry to confuse it with? And if there is, wouldn't it be blindingly obvious what is meant if you read the post?

End result, OP could have written KWH, kwh, KWh, kWH, KwH or kWh and 99.9999% of readers would have perfectly understood what was being refered to.

Correcting other peoples spelling or use of SI units really doesn't add anything useful to the point being made.

</rant>

MP

tomstickland

cm233lh wrote: »

Incidentally, that should be kWh, not Kwh.
these are international symbols and if you use them incorrectly then you risk being misunderstood.

I think the risk is pretty small!

units (Kilowatt hours, aka Kwh).

I've even written out in plain English what the units are.

Incisor

mute_posting wrote: »

<rant>
I don't think anyone on this discussion was likely to get mixed up, really (given the context the units were being used in)...

AFAIK there is no "K" prefix, so it is unlikely to make any difference (to people's understanding) if OP writes "k" or "K". Likewise with the Watt unit - AFAIK there is no unit denoted by a lower case "w".

As for the "h", should that be miss-typed in upper-case, is there such a thing as a Watt-Henry to confuse it with? And if there is, wouldn't it be blindingly obvious what is meant if you read the post?

End result, OP could have written KWH, kwh, KWh, kWH, KwH or kWh and 99.9999% of readers would have perfectly understood what was being refered to.

Correcting other peoples spelling or use of SI units really doesn't add anything useful to the point being made.

</rant>

MP

Enjoyed your rant, but why is there an ISO standard to cover this point?

Would you have defended someone writing kW/h? Common mistake, and I don't think it does harm to point this stuff out once in a while.

mute_posting

Incisor wrote: »

Enjoyed your rant, but why is there an ISO standard to cover this point?

Would you have defended someone writing kW/h? Common mistake, and I don't think it does harm to point this stuff out once in a while.

If the ISO you refer to is ISO 31, that is only a "style guide" of "reccomended" usage.

I would actually if it were on these boards and somebody was trying to express how many units they were using.

these are international symbols and if you use them incorrectly then you risk being misunderstood.

Had they being picking up something like a claim that a kettle "used x ampres to boil 1 litre of water" then fine, there is something to discuss and correct.

But correcting incorrect capitalisation of units is just comes across as smug and petty IMHO

The post got my back up because of the high and mighty "superiorirty", and, as OP pointed out they had qualified the unit in words in the post cm233lh quoted as a "risk" of being misunderstood.

MP