Just stand outside in the warm blast of air from a blower as it heats the street, to feel the nonsense of it.
In a climate of energy price hikes and dwindling resources, we all try to save it at home; but nip down to the high street to do your shopping, and it is a different story.
It would be madness to heat the house and throw open the windows and doors. But this is exactly what happens in many chain shops. Well over 20,000 UK shops squander energy out of an open door and heat the street.
That waste equates to 31,000 car miles in CO2 emissions every year for each small to medium sized shop, even more for bigger ones. The result is, we all pay - in the price of goods, in CO2 emissions and in the physical discomfort of staff and customers.
For once, a simple solution
Solutions to many of our energy problems require complex technology and years of research. Here, for once, the answer is simple and business friendly.
The Close the Door campaign was set up to make the policy common practice. By raising awareness and with an easy and efficient approach the campaign shows that everyone can be a part of saving money and energy, retailers and customers alike.
Independent data from Cambridge University engineering department provides stark information about the consequences of keeping the shop door open.
For a small to medium sized high street store (think of a Ryman Stationers, for example) an annual 10 tonnes of CO2 emissions goes straight out of the open door. If this is difficult to imagine, bear in mind those car miles and look at another equivalent: 3 return flights to Hong Kong.
Shut that door!
By closing the door when the heating goes on, all that energy and CO2 is saved. This doesn't even include figures for use of air conditioning in the summer.
Close the door, and heating only needs to be on for a short period in the day, while the overall temperature can be kept lower and even across the shop.
No more customers struggling in and out of coats, purple in the face and thoroughly distracted. No staff having to work outside guidelines for a healthy working temperature, either too hot near heaters blasting out to counteract the open door, or too cold.
Every winter there are complaints from staff to the campaign after they have been off work with a virus, returned to work in these conditions, and ended up taking more sick days off.
There is a myth in retail that customers won't come in through a closed door. The obvious and depressing implication of this is that customers are stupid, or that what is on offer is not worth passing through a door for.
Leading by example
The good news is that several large retailers have done their research and wholeheartedly adopted a closed door policy, because it works just as logic suggests; Vodafone is one, Costa coffee is another.
The proof is there in the thousands of shops, of all types and sizes across the country, trading successfully with a closed door policy. New York has legislation for this policy, and it is one of the world's great shopping destinations.
Independent retailers, who have to keep a close eye on their bills, almost invariably close their doors. Now major chains such as the John Lewis Partnership, M&S and Tesco are firmly behind Close the Door.
There is wide support right across the political parties and heavy-weight endorsement from well known scientists and business figures, and also from Usdaw, the shop workers union.
Retailers are well aware of the marketing value of promoting sustainability and making grand corporate social responsibility claims. However, we should be alert to ‘green wash'.
In freezing January earlier this year the Lush chain, so loud about its ethics, had posters beside some of its wide open doors, belting heat out and proclaiming "What's Good for the Climate is Good for the Economy".
This flagrantly played on customers' concerns, apparently on the assumption they wouldn't notice the contradiction. It might as well have been a 'Save Water' poster in a drought with a hose left running beside it.
An often repeated response is "but we do xyz to save energy instead of closing the door". When you can do something as simple as closing the door to make a major difference, this excuse does not cut the mustard.
Another excuse we come across is that the use of an over-door blower does the job of a closed door. To get it straight, those heated blowers are just that; heated blowers. They do not somehow keep the air in the shop separate from the air outside - because they are not magic.
The different device of an air curtain is disrupted by passage through it and so is unsuitable for use near doorways. It is not particularly efficient even in a more sensible place.
From the Cambridge University data, one heat blower over a single door uses energy equivalent to driving a bus from London to Glasgow and back, every week. Just stand outside in the warm blast of air from a blower as it heats the street, to feel the nonsense of it.
Disabled access a red herring
What about disabled legislation saying the door must stay open, or mothers with buggies? Cambridge City Council Planning Department and disabled groups advised the campaign that access is a vital issue, but insisted that leaving the door wide open is never a sensible answer.
Rather, disabled people may be less able to move out of drafts or away from very hot areas in the shop created when the door is open. There is a BBC clip on the campaign home page featuring a toyshop, whose owner gives the low-down on how to trade successfully with the door shut, and there are buggies galore in that.
Staff do need to be available to open the door and help, and that translates into a warm welcome and eventually profit; it doesn't even mean having to employ more staff. It's a simple issue of retraining.
Funnily enough, Mums with buggies are generally not in favour of the consequences of energy waste for themselves or their children - or of children being able to run out of the shop unhindered.
If you add to this the issue of air pollution on the street outside shops, then a closed door helps again. Research from Kings College London and Edinburgh University shows serious long term health implications from high levels of air pollution.
It's is a particular problem in London and across UK cities due to vehicle emissions. Nanoparticles, mainly from diesel emissions, are small enough to cross the lung lining and enter the blood stream and can cause heart disease and lung cancer.
This is a proven hazard to people working on busy streets and, by implication, to staff in shops with open doors to these streets. Dr Ben Barratt of KCL will be conducting independent research on the retail environment in an area of high pollution in London in 2014.
In the meantime the advice is that shop doors should be closed when pollution levels are high to protect staff and customers.
Close the Door campaigns to change policy from branch to board level, and customers can make a crucial difference too. Closing the door behind you, supporting shops that follow the policy, and politely making your concerns known in those that do not, are all steps towards positive change.
The key is customer demand
During campaign discussions with Body Shop only last week, we asked what one thing would bring the policy into place for the business and the answer came: customer demand.
There is more detail on the campaign website and everyone is invited to click through from the home page to like the campaign Facebook page and follow the Twitter feed; every time this happens the collective voice gets louder.
Raising awareness on every level is what works in making a simple change with big effects. Saving our resources and stopping CO2 reaching the atmosphere can be as easy as closing the door.
Jeannie Dawkins is Director of the Close the Door Campaign. She founded Close the Door in 2007 with Sian Reid, as a local initiative. This has now become an award winning national campaign.