People are being told to wear jumpers instead of relying on patio heaters, in an attempt to cut carbon emissions.
Campaigners say patio heaters emit too much CO2
The Energy Saving Trust has urged retailers to stop selling the heaters after a report suggesting their use will almost double over the next year.
It says the number of privately owned units in the UK will rise from 1.2 million to 2.3 million.
Each heater uses the same amount of energy in six months as a kitchen gas hob does in a year, the Trust said.
Chief executive Philip Sellwood said: "Why don't people just wear a jumper?"
After interviewing 1,192 UK households, researchers found that Yorkshire and Humberside had the highest rate of current or intended patio heater owners, on 18%.
The lowest rate was in the East of England, on 3%.
Two-thirds of patio heater owners said they used theirs once or twice a week.
Half of owners switched theirs on during the hottest months of the year, July and August.
Mr Sellwood said: "We are calling for responsible retailers to reconsider the sale of patio heaters in light of the substantial amount of carbon emissions they produce."
It is thought that the recently imposed smoking ban in enclosed public places in England will lead to more outdoor smoking and an increase in commercial patio heaters.
Mr Sellwood said: "People are also influencing the larger, more damaging commercial sector, with a third of pub-goers choosing pubs where there is a patio heater.
"Landlords are helping to make patio heaters desirable - which they are not."
Some 31% of people who responded to the survey said they liked to sit outside pubs and would choose one with outdoor heating.
Last month, London Mayor Ken Livingstone called for a halt in the spread of "wasteful" patio heaters and urged retailers not to promote them.