Why do Canberrans keep their heaters off until Anzac Day?

But it's often spoiled somewhat, especially for sophomore Canberrans like myself, by someone who is ACT born and bred, telling you not to turn your heater on until Anzac Day. True Canberrans can last until this unofficial milestone, apparently, toughing it out no matter how old and uninsulated their home.

Some people proudly adhere to it, others sheepishly cave in, and others seem to take the rule as seriously as many other Canberrans take using their indicators while driving (not at all). I've wondered if it is a weird hazing ritual, and my colleagues are secretly laughing at me at home in my two jumpers while they are toasty in their own homes.

It's a uniquely Canberra thing, as far as I can tell. I've lived in other cold places and the only thing that stops people heating their houses is whether they have a load of firewood ready.

But where does it come from? Why do Canberrans say you shouldn't turn your heater on before Anzac Day?

For a small city with a short history, it shouldn't have been that hard to find out.

I've annoyed historians on family bike rides, been laughed at, told that their expertise was on much more important topics, and given helpful lists of names of others who may know the answer. I've called people I wasn't even sure were still alive.

But call after call to historians specialising in various aspects of the capital's history left the picture as hazy as the sky when everyone in the street has their fire roaring in a valley.

Theories abound online from where the "rule" comes from. Was it that the public housing flats wouldn't be heated until after Anzac Day? The ABC debunked that one a few years ago. Next.

Is the rule followed at the university residential halls? Did that start the "rule" for the rest of us?

Historian Stephen Foster quite literally wrote the book on Australian National University. While he has heard of the rule, he doesn't believe it can be traced back to the university.

What he could explain is that old central heating systems had to have a start date, because once they were turned on, it was too costly to continue turning them on and off again, so it would be necessary to wait until it was properly cold.

"If you start burning oil, you start burning money."

Is it the military barracks? Well, no one at Defence knew and their media department helpfully suggested I read a book on the history of Duntroon to maybe find the answer.

Another theory is that the hostels built after World War II to house the influx of public servants wouldn't turn the heaters on until after April 25.

Local author and historian Alan Foskett laughs at that suggestion and said: "I'm sure it would have been a general rule - for the hostels that had heating".

Mr Foskett arrived in Canberra from Sydney in 1950 as a young public servant, staying in what was then Reid House until 1952. There was no heating or water in that hostel, so no such rule applied, but he remembers the rule existing way back when he was new to the city.

The Canberra and District Historical Society also had little to tell me, but a post on their Facebook page revealed even more theories.

Canberran Sally Bond, whose grandmother was born in Goulburn and moved to Canberra in the 1960s, said the tradition came not from heating, but actual fires.

"She always said the fires were lit on Anzac Day and stoked all through winter until the October long weekend.

"She then kept this tradition with electric heating, resisting the urge to turn it on before Anzac Day. She passed this tradition down to me and my sisters too."

Another member of the historical society said the tradition could be traced back to the 1940s in their family.

Cally Earnshaw, manager of visitor and community services at Lanyon Homestead, said such effort was required for old fires to be created for heating and cooking, it was important to make sure once a fire was lit, it wouldn't be extinguished.

Ms Earnshaw said she didn't know the origin of the rule and that it didn't come from historical houses like Lanyon - they existed long before Anzac Day was marked on calendars.

One thing is for certain, and that is that it is slowly becoming easier to delay turning on one's heater. According to Bureau of Meteorology climatologist Felicity Gamble, April's maximum and minimum temperatures have been trending upwards since they first began to be measured at Canberra airport.

"The trend is in line with the Australian average temperatures, which is roughly one degree per 100 years, that Canberra data is roughly in line with that," Ms Gamble said.

"We're getting fewer colder Aprils and more warmer Aprils."

The average minimum temperature measured throughout April at the Canberra airport site in 1939 was 8.6 degrees, with no mornings dipping below zero.

Last year the average minimum for the month of April was 8.7 degrees, but Ms Gamble warns the two numbers aren't a direct comparison, because the location of Canberra airport's thermostat was moved to a new spot in 2011.

A straight comparison of two years doesn't necessarily give the full picture, which is why the trend is what's measured.

If you have been feeling like it has been easier to stick to the Anzac Day rule in recent years, that may be because the last time Canberra airport recorded a minimum April temperature below zero was in 2011 - and that was Anzac Day itself, at -1.1.

While the cold nights and cold mornings may not be as bad as those experienced by Sally Bond's grandmother, Ms Gamble says people get used to the temperatures in their area and that must be taken into consideration.

"If you have had a warm summer and a warm March and the temperatures do drop off a bit, people do feel that quite significantly."

So do people actually stick to it? We can lie in the office, but not to our energy providers.

According to ActewAGL, their data shows a noticeable uptick in people using energy in the first week of May, but acting general manager of retail Rachael Turner says they can't be sure if that is because people are holding off, or because it's actually getting colder and people need their heaters more.

"I think it could be a bit of both, definitely the cooler weather is setting in. But certainly we hear about this tradition," Ms Turner said.

"We looked at our data from last year and the usage data shows that Canberrans used around 25 per cent more energy in May than in April."

Ms Turner said space heating accounts for about 60 per cent on Canberrans' energy bills, and that the company had many measures in place to help people save on using power but also help with paying their bills.

While Ms Turner had many answers about how people use their heating, acknowledging many of her friends stuck to the rule, she didn't know where the rule came from.

Looking ahead to Anzac Day, the whole argument seems somewhat futile - the bureau isn't forecasting a minimum temperature below nine degrees all week.

There's already been a 0.5 and a 2-degree minimum, but I have barely worn my slippers, let alone put the heater on this year.

I know I won't be shivering in the name of a tradition that I still can't find the origin of, but I probably can thank climate change, not my resolve, to thank for that.