Cost of running a tumble drier help please

Martyn_H

Hello

Could someone with a head for maths please work out what it costs to run a 3.3kwh drier for 30 minutes assuming a unit rate of 9.35p (N-power's April 2009 price).

I'd appreciate it if you could show how to work it out.

Many thanks.

CrashUK

it would cost about 16p

Ben84

Calculating the cost to use an appliance takes a few steps, and you will always need the cost per unit (or kWh, same thing) of electric, the energy in kW consumed by the appliance, and the time it's used for.

As electric is billed by the kWh, which is 1000 watts per hour, you must make sure you are using the wattage of the appliance in kW in the calculation. If given in watts, simply divide by 1000 to turn in to a fraction of a kW.

A 250 watt hair dryer for example is 250/1000 = 0.25 kW.

Had your tumble dryer been given as 3300 watt, dividing by 1000 would give the figure 3.3 kW.

Same amount of energy, simply a different way of describing it. Much like 100 cm is 1 meter. People sometimes get confused by this when converting, but really the units are about how you look at the amount based on how it is divided. Just as 1 liter is 1000 ml, because you're counting the quantity in smaller amounts.

Now you have a figure in kW, you can simply multiply the appliance's kW rating by your cost for a kWh to find the cost per hour of use, as this is how many kW you would have to buy to run the appliance for an hour.

This figure is probably useful enough in most cases, but if you want to know the cost for any amount of time you can multiply or divide to find it. In your case, divide by two to find half an hour of use, or you could divide by three to find the cost for twenty-minutes.

If however you want to find a strange number of minutes use that isn't an obvious division from an hour, you can divide the cost for an hour of use by 60 to find the cost per minute, then multiply by the number of minutes you want to know the cost of.

To apply this to your tumble dryer:

Wattage is already in kW, so 3.3 x 9.35 = 30.9p for an hour of use

30.9 / 2 = 15.5p for half an hour


We can also find this figure by the second method:

30.9 / 60 = 0.52p per minute

0.52 x 30 = 15.5p for half an hour

Hope this makes sense and helps.

As an extra, because this is the green and ethical forum, so I'm going to add that you can also very easily calculate the amount of CO2 emitted in to the atmosphere as well. My last electric bill said that the UK average CO2 emissions per kWh of electric are 0.467 Kg. You can multiply your figure in kWh by this to find how much CO2 your appliance emits in to the atmosphere when used. For example:

3.3 kW x 0.467 Kg = 1.5 Kg of carbon dioxide for every hour used.

Martyn_H

Thank you all very much. I'm concerned because, as a family of three living in a 1930s semi and cooking by electric, we are using 5987 units a year. Apparently the average is 3300 units.

Cardew

The above calculations are on the assumption that the tumble dryer is drawing the full 3.3kW* for the 30 mins.

Many dryers do not use the full power for the whole of the cycle. You need to get a plug in power measuring meter to get an accurate reading of consumption.

* Are you sure it is 3.3kW? that is an unusual rating for a UK appliance

Martyn_H

Cardew wrote: »

The above calculations are on the assumption that the tumble dryer is drawing the full 3.3kW* for the 30 mins.

Many dryers do not use the full power for the whole of the cycle. You need to get a plug in power measuring meter to get an accurate reading of consumption.

* Are you sure it is 3.3kW? that is an unusual rating for a UK appliance

When I looked on the internet, it said the Whirlpool AWZ 3303 is rated at 3.3kwh - a 'C' for power consumption.

I've just tested a kettle with a plug in reader and that seemed normal.

Cardew

Martyn_H wrote: »

When I looked on the internet, it said the Whirlpool AWZ 3303 is rated at 3.3kwh - a 'C' for power consumption.

I've just tested a kettle with a plug in reader and that seemed normal.

You have misread the technical specification.

The rating of any electrical appliance is always in kW not kWh.

The Tech spec states it uses 3.3kWh for a full load.

It is rated at 2.5kW - which is normal for a tumble dryer.

Whirlpool AWZ3303 has a noise level of 65 dBA which is considered low and quieter. The connected load of Whirlpool AWZ3303 is 2500 Watts. The voltage is said to be 230 – 240 Volts. Whirlpool AWZ3303 has been rated for energy efficiency as grade ‘C’.

2500 Watts is 2.5kW.

So 30 minutes use will consume 1.25kWh, if it is on full heat for the whole time. costing approx 12p.

Martyn_H

Thanks Cardew. This is why I don't trust myself to do the maths. 12p x 4 times a week is hardly going to break the bank, so I'm surprised that people tell me that tumble driers are expensive to run.

Returning to my comments about the kettle, the figure from the power reader at least suggests that my electricity meter is working properly. I don't want to spend £80 on having the meter checked if I can avoid it.

Jojo_the_Tightfisted

It's certainly cheaper than having to rewash things because they began to get musty as there wasn't a suitable drying area. But I do have a flat, not a house with space for drying outside - I'm sure you take advantage of that during dry periods, though.

In summer, rather than using the tumble dryer, I put the clothes on the airer and switch on the fan, as I needed airflow, not heat, so I saved a bit that way, too.

Fire_Fox

Martyn_H wrote: »

Thanks Cardew. This is why I don't trust myself to do the maths. 12p x 4 times a week is hardly going to break the bank, so I'm surprised that people tell me that tumble driers are expensive to run.

According to the Energy Saving Trust the average washing machine is used 274 times a year, the average tumble dryer 148 times a year. Obviously some households are using a lot more and others a lot less: many families on these boards report using their TD daily for an hour or more year round! As most families have access to outside space and hanging out laundry is not time consuming, it's an easy place to save money and the planet.

Fire_Fox

Jojo_the_Tightfisted wrote: »

It's certainly cheaper than having to rewash things because they began to get musty as there wasn't a suitable drying area. But I do have a flat, not a house with space for drying outside - I'm sure you take advantage of that during dry periods, though.

In summer, rather than using the tumble dryer, I put the clothes on the airer and switch on the fan, as I needed airflow, not heat, so I saved a bit that way, too.

I live in a north-facing flat with no outside space and never use my dryer - I have this
http://www.ikea.com/gb/en/catalog/products/80119043
It will comfortably take two loads of laundry, has a two foot square footprint and folds flat when not in use. It lives in my bedroom - with the window partially open it takes half a day for everything to dry in the summer and a maximum of two days (jeans) in the winter, and I am not big on heating! I know it sounds sad but this airer is one of the best things I have bought for my flat.