This bill increases the limit on the energy efficient home improvement tax credit to $4,000 (from $2,000) for the cost of an electric or natural gas heat pump, an electric or natural gas heat pump water heater, a biomass stove, or a biomass boiler.Under current law, a taxpayer may claim a nonrefundable tax credit of 30% of the cost, up to $2,000, for an electric or natural gas heat pump, an electric or natural gas heat pump water heater, a biomass stove, or a biomass boiler for a principal residence. (Under current law, taxpayers may also claim a nonrefundable tax credit of 30% of the costs, up to $1,200, for certain other eligible energy-efficient property such that some taxpayers may qualify for a maximum tax credit of $3,200.)