More Americans are buying heat pumps, an environmentally friendly alternative to furnaces and air-conditioners that can significantly lower monthly energy bills. But the pace of installations has slowed in the past year, posing an obstacle to the Biden administration’s climate plans. Rising interest rates and inflation combined with a slow and confusing rollout of federal government incentives for the purchase of heat pumps are largely responsible for the recent drop in sales, energy analysts said. These headwinds, if they persist, could jeopardize President Biden’s goals of effectively eliminating U.S. emissions of greenhouse gases by 2050. Mr. Biden’s signature climate law,…