TOKYO >> Hitoshi Tamura makes sure the curry restaurants he operates in Tomakomai, Hokkaido, take all the necessary precautions against COVID-19.

Customers are asked to wear masks, disinfect their hands and take their temperatures. Transparent panels stand between cashiers and guests. Diners pick up their own orders.

But the often freezing climate during winter is proving to be a challenge to businesses struggling to keep their spaces well-ventilated.

“This wasn’t an issue during the summer, but this winter, it’s just too cold over here. We turn up the heat when we periodically let in outside air, but that’s not enough to keep the venues warm,” said Tamura, owner of Tam House Curry Lab, a small restaurant chain specializing in orthodox curry and soup curry, invented in Hokkaido.

Recently, temperatures in Tomakomai have hovered at 32 degrees but have dropped at times to 14 degrees.

“We use kerosene stoves since (heaters) aren’t powerful enough, but the costs are insane,” Tamura said. “And for customers sitting near the entrance, the cold draft seeping in can be uncomfortable.”

As a third wave of infections sweeps through Japan, large cities in Hokkaido, known for its frigid winters, have seen surges in COVID-19 transmissions. And with the situation expected to worsen, Japan’s government has stressed ventilating indoor spaces. It recommends opening doors and windows at least twice an hour to purge stale air.

Yasutoshi Nishimura, who leads Japan’s pandemic response, urged the country to utilize digital sensors that measure carbon dioxide levels in the air. The higher the levels in a room, the greater the probability of transmission. He advised businesses to provide ventilation, guided by sensor readings.

Soon after, Maspro Denkoh Corp., a maker of television parts, began selling a carbon dioxide detector for $480. “We’ve already sold 500 to 600 of these sensors, many to restaurants and fitness gyms,” said salesman Kohei Marui. Other companies have followed suit.

Now, Daikin Industries Ltd., the world’s largest manufacturer of air conditioners, offers a cutting-edge solution: technology that brings outside air indoors. (Most air conditioners recirculate indoor air.) This one also brings the outside air to indoor temperatures.

These high-tech ventilation systems are pricey. A wall-mounted version for a 230-square-foot room costs about $1,900. A ceiling-­mounted unit is $5,000.

To promote advanced ventilation devices, the environment ministry earmarked nearly $29 million to subsidize restaurants and supermarkets. About 850 busi­nes­ses are set to receive funding.

But that helps just a fraction of restaurants, and investing in a ventilation system isn’t a fix-all. Stay-at-home requests and the suspension of government restaurant promotion programs mean many eateries are facing a bleak winter.

Some restaurants are revamping.

“I’m focusing on shifting the weight of our operation toward online sales,” said Tamura, the curry restaurant owner. “I’m anticipating that the pandemic won’t be going away anytime soon.”