A study found other people had to use makeshift solutions like taping tin foil, cardboard, or damp sheets to windows.
One in six Britons are taking “drastic action” such as sleeping in the kitchen, missing work or booking hotels to cope with the heatwaves, Citizens Advice has found.
The charity said millions of people across the UK are “trapped in homes they can’t cool”, finding almost half (44%) feel they lack basic control to stop their houses overheating.
It is demanding Government action on a “now year-round crisis” of “soaring heat in summer and unaffordable energy bills in winter”.
Action taken by those struggling to cope included sleeping in unconventional places like the kitchen, garden, or on a balcony, taking sick days, unpaid leave or annual leave, or paying for hotels.
A further four million said they had to use makeshift solutions like taping tin foil, cardboard, or damp sheets to windows.
The study found poorly designed homes, which act like “heat traps”, and the high cost of cooling equipment such as air conditioning were making people feel helpless against the hot weather.
Half (51%) of tenants – including those who rent privately and those in social housing – felt they lack the basic control needed to stop their homes overheating, compared with 40% of homeowners, the poll found.
The study also found 90,000 heat network consumers were unable to turn off their central heating even in summer.
Citizens Advice chief executive Dame Clare Moriarty said: “For far too many people, a summer heatwave doesn’t mean enjoying the sun – it means being trapped in a sweltering home with no control over the temperature.
“We’re now facing a year-round crisis, where poorly designed housing stock is acting as a giant heat trap in summer and as an ice box in winter.
“The Government has a vital opportunity to help fix this through the Warm Homes Plan. By investing in better insulation, ventilation, and heat network upgrades, we can ensure people’s homes are warmer in the winter and safer and cooler in the summer.”
A Government spokesman said: “We are changing the rules so that for the first time ever people can access grants for air-to-air heat pumps, which can cool as well as heat homes.
“We are already taking action to strengthen protections for tenants experiencing dangerous overheating and ensuring new residential buildings are designed to minimise unwanted heat from the sun.”
Yonder surveyed 2,105 UK adults on July 1-2.
