When the sales representative from Summit Natural Gas of Maine discussed Peter Sillin’s options for converting to the cost-efficient fuel, only one contractor came up: Dave Ireland Builders LLC.

In addition to referrals from Summit itself, David Ireland marketed his services directly to homeowners by offering a dozen hours of free insulation work, and state and private rebates. He also distributed mailers showing his company’s logo next to Summit’s under the banner “Your partners in energy efficiency.”

In a customer worksheet distributed by Summit sales representative Bridget Doxsee – who made the pitch to Sillin – Dave Ireland Builders was the only business listed in the section where the company suggested that customers receive multiple estimates.

“I would have never known about Dave Ireland Builders if they had not been recommended during the presentation,” said Sillin, who lives on Main Street in Yarmouth. “It was to a certain extent on the basis of that recommendation that I felt comfortable going with a company that I had not previously heard of.”

Sillin is among the dozens of Summit Natural Gas customers in Yarmouth, Falmouth and Cumberland who gave the Howland-based contractor deposits of between $1,500 and $3,500 to convert their home heating systems to natural gas. Last week, however, Ireland abruptly shut his business down, leaving Sillin and many others in the lurch. Now the Consumer Protection Division of the state Attorney General’s Office is looking into the case, asking residents to contact the office if they gave Ireland money and have not received services.

Summit, for its part, is trying to distance itself from Ireland, saying his company was among the list of capable businesses approved by the Better Business Bureau and provided by Efficiency Maine.

“For our customers in southern and central Maine who may have independently contracted with Dave Ireland, LLC for natural gas conversion service, we encourage them to call our Augusta office at 621-8000 and we will provide a variety of resources to them,” said Mike Duguay, director of business development for Summit Natural Gas of Maine.

Duguay, who spoke Monday night before the Cumberland Town Council, refused to explain why his company’s logo appeared next to Ireland’s, why his sales staff promoted Ireland to potential customers, and whether the company had any knowledge of Ireland’s financial situation before he closed.

“We’ve issued our statement,” Duguay said, before hastily leaving the building.

Cumberland Town Manager William Shane was among the people who questioned Duguay’s assertion that Summit had no relationship with Ireland’s business.

“Right from day one, your sales staff was directing people to (Ireland),” Shane told Duguay. “I don’t know him from Adam, and they brought him to our home.”

Under the state’s utility regulations, it is legal for a natural gas supplier such as Summit to promote a contractor that the utility deems suitable to perform the work, said a spokesman for the Maine Public Utilities Commission.

But now that Summit is backing away from the contractor, residents in Cumberland are angry.

Perhaps the most vocal critic of Summit on Monday night was David Ginsberg. He said the stacks of a flier showing a handshake, Summit’s logo and Ireland’s logo under the words “Your partners in energy efficiency” were available at the Summit field office, and were distributed to customers in Summit-branded folders of information. Ginsberg, who lost about $2,500 to Ireland, said that after countless phone calls, Ireland finally called Ginsberg back last week and promised that someone would soon cut him a check to settle his debts.

“David Ireland told me personally that he was $1 million in the hole,” Ginsberg said. “I feel taken advantage of.”

David Goldman, an attorney who lives in the Crossing Brook neighborhood, said his installation was delayed several times by Ireland’s company until he learned it was out of business. Immediately, he filed a lawsuit.

“I started talking with other people in my neighborhood who are in a similar situation,” Goldman said. “People who aren’t lawyers don’t necessarily know what to do.”

Ireland, who was a longtime insulation and weatherization contractor, recently expanded into the heating, ventilation and air conditioning business.

He could not be contacted Monday. No one answered the phone at his business line, and his voice mailbox was full. A spokesman for the Attorney General’s Office said Ireland has not returned the office’s calls, either.

The Cumberland Police Department is the lead agency in the investigation. As of Monday evening, 16 residents have come forward to police. Many more have made complaints to the Attorney General’s Office, said Police Chief Joe Charron.

Jason Lamb, who was hired by Ireland about eight months ago as the vice president of the heating, ventilation and air conditioning arm of the business, said he and Ireland met with a representative of Summit multiple times to discuss the conversion process.

“(Summit) had general questions about how the installations would go, how many installations we could do,” Lamb said. “We had more work than most other contractors around. It just befuddles me that this happened.”

Ireland’s traction with customers who had never dealt with him before could be linked to his unusually low prices.

“He was 20 percent below most contractors,” said Shane, the Cumberland town manager. “Most (other contractors) said they were not going to compete at that level.”

The state’s Consumer Protection Division can be contacted at 626-8849.