New restrictions are being added in December to the $25 rebates that National Fuel Gas Co. customers can receive for installing programmable thermostats.

While consumers currently can receive the rebate simply by purchasing a qualifying thermostat, new standards that will take effect Dec. 1 will limit those rebates to only thermostats that are installed as part of a larger-scale project to replace a furnace or boiler, said Jessica Manocchio, a National Fuel spokeswoman.

The change adds a further restriction to the Amherstbased energy company’s two-year- old conservation incentive program. Revisions announced two weeks ago by the state Public Service Commission included the elimination of the $150 rebates currently available on the purchase of a new energy-efficient hot water tank and the $350 rebates on tankless water heaters.

PSC officials said at the time those rebates were being eliminated because their cost did not match the energy savings they produced. The revised program, beginning in December, is adding a $300 rebate for indirect water heaters with an efficiency rating of at least 90 percent.

The rebate program, which began in December 2007, has paid out more than 12,000 rebates for programmable thermostats. Most of those rebates were for thermostats purchased in conjunction with a new furnace or boiler, Manocchio said.