In 1984, Nelson & Small Inc. of Portland began distributing a direct-vent heater from Japan. It sipped kerosene, when most heating systems guzzled oil.

By the mid-1990s, Maine had become the top American market for the super-efficient heaters imported by Monitor Products Inc. Soaring power rates had Mainers tearing out electric baseboards and looking for alternatives. Many residents chose the Monitor kerosene heater, and up to 75,000 homes and businesses are warmed by the units today.

Now that growth has ended. Nelson & Small received a letter last winter from Monitor with unwelcome news: The Japanese manufacturer, Hitachi, has stopped making the heater. Parts will be made at least through 2014, and warranties will be honored. But after dealers sell the units they have in stock, no more Monitor.

Also discontinued is the natural gas and propane version of the Monitor heater.

With another heating season approaching, the region’s wholesaler and southern Maine’s leading dealer say customers shouldn’t worry about parts or service. They also say the reliable, little heaters can be kept running for many years to come.

“There’s no reason for anyone to panic or to pull a unit out,” said David Small, chief operating officer at Nelson & Small.

Small’s company is the exclusive Monitor wholesaler in New England and upstate New York. It has been stockpiling parts to maintain a large inventory.

“Japan is far away, and it’s a long heating season,” he said.

The American market for the Monitor kerosene heater and its chief competitor, Toyotomi, grew out of a portable, wick-burning unit sold after the first oil-price shock in the early 1970s. Questions about safety and indoor air quality put KeroSun out of business, however, and some of the managers gravitated to a trading company in Japan to sell a new technology.

The Monitor and Toyotomi designs feature a direct-vent system that pulls combustion air from outdoors and sends exhaust gases back through a double-walled pipe. Net efficiency is rated at 88 percent, and many customers heat 1,500 square foot homes with fewer than 500 gallons a year. Fuel economy and low installation costs made the heaters popular in cold-weather climates with high energy prices, including the Northeast, the Pacific Northwest and Alaska.

With Monitor gone, customers looking for a new, direct-vent heater that burns kerosene are left with Toyotomi’s Laser heaters. Toyotomi also makes a model that burns heating oil. Another is approved for ultra-low-sulfur diesel, which is being phased in for Maine.

“We believe it’s going to become the home heating fuel of choice,” Small said of ultra-low-sulfur diesel.

But fuel prices may be a factor in consumer demand. In the past few years, high oil and kerosene prices and stricter regulations for tank installations have led many customers to prefer direct-vent heaters that burn natural gas and propane. The best-known option is the series of heaters made by Japan-based Rinnai Corp.

Monitor, Toyotomi and Rinnai heaters are carried by Frederick Bros. Oil and Propane in Scarborough. The company has installed thousands of Monitor heaters over the past 22 years, according to Nathan Frederick, the sales manager. It also sells used and reconditioned units.

Frederick has a few new Monitor heaters in stock. The kerosene models sell for roughly $1,500; the gas units are $1,199.

Frederick said he prefers the quality of some earlier models, which can be easily repaired and last more than 20 years. Some customers are learning about Monitor’s exit and asking what to do. In most cases, Frederick suggests keeping their unit and maintaining it as needed.

“We do cleanings on them every day of the year,” he said. “We tell people, ‘If it ain’t broke, don’t fix it.’ “

Staff Writer Tux Turkel can be contacted at 791-6462 or at: tturkel@pressherald.com