For one GP, the very thought of people keeping windows tight shut “makes his head explode with anger”.
And a leading engineer says he embarrasses his family in restaurants “by going around trying to bring in fresh air”.
They are part of a growing band of medics and experts worried about how the coronavirus can accumulate in stuffy rooms.
And with people gathering indoors in the winter months, they say the authorities need to emphasise the importance of outside air.
What is the problem?
According to the GP, Eilir Hughes, who runs a surgery in north Wales, the government slogan “hands, space, face” doesn’t go far enough.
It appears on the lectern used by Boris Johnson in Downing Street briefings which gives it massive prominence.
But Dr Hughes – who has become known as “Dr Fresh Air” for his campaigning on the issue – believes it should say “hands, space, face, replace”.
He says replacing stale air in a room with fresh air from outside can massively reduce the chances of people becoming infected.
The council in Anglesey is believed to be the first in the UK to display banners spelling out the four-word slogan.
Dr Hughes says the new message has attracted attention around the world.
“I say to people: ‘Give the gift of fresh air this Christmas.'”
What does the science say?
At the start of the pandemic, the authorities focused on what were assumed to be the most likely routes of infection.
One is the risk of touching a contaminated surface – hence the longstanding guidance to keep washing your hands.
The other is being hit by droplets produced when someone nearby coughs or sneezes – that led first to the 2m rule for social distancing and later to face coverings.
But the possibility of a third route of transmission – through tiny virus particles known as aerosols lingering in the air – is now widely accepted as well.
In the past few days, the US authorities have gone further by saying that inhalation of droplets and aerosols is “thought to be the main way the virus spreads”.
And faced with that risk, handwashing, social distancing and mask wearing are no guarantee of defence.
Do open windows really make a difference?
Shaun Fitzgerald is convinced they do, and he has made it a personal mission to improve ventilation wherever he can.
He is a Royal Academy of Engineering professor at Cambridge University, but that doesn’t stop him from “trying to wrench open windows that have been painted shut or haven’t been maintained for years”.
“I have to walk out if I can’t open them – I refuse to be in a place that is not well-ventilated.”
According to Dr Fitzgerald, the research shows that bringing in a good supply of fresh air to dilute and disperse the virus can cut the risk of infection by 70-80%.
He supports the messaging on handwashing, social distancing and face coverings, but says fresh air “is always the fourth on the list or often not there at all”.
“My concern is that winter cold hasn’t hit us round the face yet, but already this season means people are indoors and windows are usually shut.
“My very grave concern is that with the new strain of the virus, we know that keeping aerosols down to a low level is going to be even more important, and that means keeping places adequately ventilated.”
What are the dangers?
Dr Fitzgerald points to recent research in a restaurant in South Korea which highlighted how far the virus can spread indoors.
With the help of contact tracing and CCTV, scientists were able to establish how one diner was able to infect two others even though one was more than 4m away and the other more than 6m away.
Even though all three were only in the same room for a matter of minutes, that was long enough for the air conditioning to drive the virus over those long distances.
“Aerosols can travel many metres once they’re airborne,” Dr Fitzgerald says.
“Two metres doesn’t buy you safety, the only thing that does is good ventilation. If they’d opened the windows in that restaurant, that might well have changed things.”
But what about letting in the cold?
Dr Fitzgerald says it is not about throwing every window open wide all day, but making sure there’s enough of a crack to let in fresh air.
And the answer is to add another layer.
“I’d recommend wearing a woolly jumper rather than just a short-sleeved top.
“But that’s what we should be doing anyway, to save on heating bills and reduce our energy demand as we all do our bit to tackle climate change.”
Dr Hughes says airing rooms for a few minutes several times a day won’t lose much heat but will keep people safer.
And his idea for a Christmas gift? Thermal underwear.