At Dyson we use the following figures in our calculations:

Number of paper towels per use = 2

This is based on our own internal research. We know that people can often take more than 2 paper towels to dry hands but we believe in estimating costs as cautiously as possible.

Paper towel cost = $0.015

This is based on our own internal research. We have taken paper towels costs from the five most popular sources and calculated the average cost across all territories.

Bathroom usage per day = 200

This is based on our own internal research into the usage of an average sized bathroom. For smaller bathrooms with low footfall we use a figure of 100, and for high footfall areas such as service stations or airport bathrooms we use a figure of 400.

Number of days the bathroom is in use = 365 days

We assume a whole year.

Electricity price per kWh = $0.10

This is based on our own internal research. We have taken electricity costs from 5 different sources and calculated the average cost across all territories.

Wattage = as stated by the manufacturer

Standby power = as stated by the manufacturer or as tested by Dyson.

Dry time is based on the National Sanitation Foundation’s Protocol P335 (NSF P335).

Annual carbon impact is calculated based on 200 uses per day, 365 days per year.

Watch out: most hand dryer manufacturers do not follow NSF P335, so may quote incorrect dry times. NSF is an independent hygiene specialist. If you want an accurate dry time, insist on the NSF P335 test results.

The annual running cost of paper towels is estimated by = 
The average number of paper towels used to dry hands x the average cost of the paper towels x the assumed number of uses per day x an assumed number of days the bathroom is in use.

There are 2 steps to this calculation.

Step 1: Running costs when in use (without standby)

Dry time of hand dryer (in hours) x rated wattage of hand dryer (kW) x the assumed number of uses per day x the assumed number of days the bathroom is in use x electricity price per kWh.

Step 2: Running costs when in use (with standby)

Result of step 1 +

((Electricity price per kWh x number of hours in a year) – (estimated uses per day (100/200/400) x dry time of hand dryer (in hours))) x Standby power (kW)

= Annual running cost

In collaboration with Carbon Trust, Dyson has produced a method to measure the environmental impact of electrical appliances and paper towels. The carbon calculations were produced using GaBi software provided by PE International, based on product use over 5 years. Dry times were measured using Dyson test method 769 based on NSF P335 with a measurement of 0.1g residual moisture.