As the first major heatwave of the summer rolls into the national capital this week with 41 degrees predicted on Thursday and a potentially record-breaking 43 on Saturday, retailers are gearing up for a run on anything to cool the air and and keep it moving. The overnight temperature on Thursday will be 18 degrees,

Grant Knight, the franchisee at Harvey Norman Fyshwick, said his store had sold "dozens and dozens" of air purifiers since easterly winds fanning the the North Black Ridge bushfire near Braidwood recently began sending plumes of grey-brown smoke across the national capital.

"The hardest thing has been getting stock," Mr Knight said.

"We're competing for stock on major brands with markets like Sydney, which has also had a huge run on air purifiers. Stores up there are calling us to buy our stock."

As the grey-brown wall again rolled into Canberra on Monday afternoon and was predicted to remain in place overnight, discomfort will be compounded by a gradual climb in temperature to 37 on Wednesday.

The ACT's Emergency Services Agency will be monitoring conditions in the days ahead and advising of whether or not a total fire ban will be called. Usually as soon as the fire danger rating reaches "severe", a total fire ban automatically kicks in.

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The retail demand for cool air will crank up in the days ahead however, as Mr Knight pointed out "it's often the day after a hot night that we see the customers coming in, desperate to get a good night's sleep".

"It's a curious thing; people who move here always hear the stories about how cold Canberra gets, but not about the heat."

The smoke has provided a huge lift in bushfire awareness across the capital. Sales of $1000 basic fire-fighting pump kits to home owners in areas exposed to bushland have soared.

"We've sold out of our most basic fire-fighting pumps," Jeff Devine, from supplier Auto Basics in Fyshwick, said. "This time last year we had sold nine, but we're now up to 27 sold and we're waiting on more."