Natural gas-powered HVAC systems and "net-zero" building codes are among the chief bones of contention in Massachusetts' carbon emissions debate.

It will ultimately be up to the next administration to decide how a new program allowing a group of cities and towns to restrict fossil fuel infrastructure buildings will operate, the Baker administration’s top energy and climate official acknowledged Wednesday, but she added that the outgoing Baker team will propose its own plan all the same.

The state’s August clean energy law created a demonstration project that will allow 10 communities to mandate that new buildings or major renovations avoid energy sources like natural gas and oil in favor of electric-powered heat, appliances and hot water. The program was one of the more controversial aspects of the law and lawmakers made late adjustments to try to allay Gov. Charlie Baker’s concerns that it could allow local leaders “to just choose not to build any housing.”

During a hearing of the Senate Global Warming and Climate Change Committee, Chairwoman Cindy Creem asked when communities that are lining up to participate will be able to move forward. The only real deadline the law set for the program is that the Department of Energy Resources must promulgate regulations for it by July 1, 2023.

Energy and Environmental Affairs Secretary Beth Card said Wednesday that her team’s “goal is to have a draft regulatory package and program established for public feedback and comment by the end of December.” So, Creem asked, will communities be able to formally apply to be part of the demonstration project by the end of the year?

“By the end of the year, they will have had opportunity to weigh in on our proposed process and then I do think, to be fair, it would be up to the next administration to finalize that package in the way that they see fit and be ready to move forward,” Card said. “But we expect to have finalized our package proposal and feedback on it by the end of the year. So it should be ready ready to go.”

Creem and Sen. Michael Barrett pressed DOER and EEA officials on whether they have accepted West Tisbury’s request to withdraw from the program out of concern it might not meet the law’s affordable housing requirements. If West Tisbury is formally removed from the program, both Boston and Somerville are waiting in the wings as potential substitutes.

“We do not have a program established yet. So we do not have an ability to accept or withdraw communities from this program,” DOER Commissioner Patrick Woodcock said. He added, “We’re trying to move this as quickly as possible, but also do it in a responsible way. So we have gotten a lot of inquiries from communities. We’re trying to engage with them to understand that we will be moving forward with this program, but it is premature to take action to apply for the program or withdraw from the program.”

The August law established two requirements for a city or town to be eligible to participate in the program: the municipality must file a home rule petition with the Legislature indicating its interest, and must either have at least 10 percent affordable housing stock under the state’s Chapter 40B law or approve a zoning ordinance allowing multi-family housing by right in a “district of reasonable size.”

But Woodcock told senators Wednesday that DOER is looking at possibly adding a data collection requirement as it writes the regulations that will guide the pilot program.

“One aspect that we want to make sure that we get right with the regulations is this is a demonstration project and it is important that we … obtain the data that would actually inform the Legislature of what this demonstration project means,” he said. The commissioner added, “There may be an established protocol that we require communities to ensure that we meet the legislative requirements of providing a report.”

The notion that the executive branch, through DOER, might impose requirements to participation above and beyond what the Legislature approved in the law did not sit well with Barrett, who has played a key role in crafting energy and climate policy during much of the Baker administration.

“Speaking as one legislator, I’m all in favor of the department gathering data. But the language doesn’t give DOER the right to delay or condition participation on the standardization of data gathering across the town,” Barrett said. “I would agree with your previous testimony that standardized data is optimal. But that’s different than conditioning participation on the community’s imposing additional data gathering requirements within their domain and delaying participation until that happens.”

Woodcock said DOER would work with cities and towns to make sure data reporting is “easy for them and easy for the department.” Barrett said he was all in favor of that “as long as the regulators do not attempt to impose additional requirements for participation beyond what the Legislature has chosen to impose, and we did not impose data standardization upon each of towns as a condition of their participating.”

The new climate law’s provisions requiring the state’s MOR-EV program to increase and expand rebates for purchasing or leasing a new or used zero-emissions vehicle were also under the Senate committee’s microscope Wednesday. Creem said the law did not provide a firm deadline for DOER to implement the new and expanded incentives, including a $3,500 minimum subsidy, and asked when they will become available.

Woodcock explained that DOER hires a vendor to run the MOR-EV program and that the contract it has with that vendor “did not anticipate some of the provisions within the new climate legislation.” So DOER last week issued a request for responses in hopes of having a new vendor able to accommodate the new requirements in place by the end of this year.

“There were a number of requirements for a electric vehicle incentive program that were established in the new legislation. The new legislation did not include funding and we know a lot of you are hard at work at trying to realize that funding and we appreciate that effort,” Woodcock said.

Instead of including new funding for the MOR-EV program and others in the clean energy law, lawmakers instead left the measure as a policy-only bill and planned to fund it through a separate $4 billion economic development bill. That economic development bill has been on ice since July 31 as Democrats struggle to salvage it amid late-arriving economic information.

“We’ve got to get the eco dev bill through before we’re going to be a position to pay for the promised EV rebates,” Baker said on GBH Radio in August.

Barrett pressed Card and Woodcock on why the administration has not increased the minimum electric vehicle subsidy to the $3,500 level that the law calls for, pointing out to them that the provision became effective the date that Baker signed the law.

“Well, understand a couple aspects of this. First, the provision that you noted does not include funding … so it is our position that the provisions within that are not mandatory to be implemented until funding is made available,” Woodcock said.

Barrett argued that the Legislature appropriated $27 million to DOER in the latest budget and that the climate law does not at all bar the department from using its appropriated money to fund the higher incentives.

“We don’t condition the increase in subsidy from 2,500 [dollars] to 3,500 [dollars] on any particular appropriation and an altogether separate economic development bill,” the senator said.

To meet its decarbonization commitments — reductions in greenhouse gas emissions of 33 percent by 2025, 50 percent by 2030, 75 percent by 2040 and at least 85 percent by 2050, all compared to the baseline of 1990 emissions — Card said that Massachusetts will need to have at least 200,000 passenger electric vehicles on the roads by 2025 and 900,000 on the roads by 2030.

“It is an aggressive goal,” Card said when Barrett asked if the 2025 target should be revised in light of a delay in the availability of a federal incentive thought to be key to getting people to adopt electric vehicles. “We know that currently there are nearly 55,000 EVs and plug-in hybrids on the road. Obviously, we can see the gap and the work that we have cut out for us.”