Determine highest "carbon reduced per dollar spent" option for reducing pollution generated by home?
Pick the low-hanging fruit.
For the vast majority of homes, improving insulation and airsealing (caulking cracks, foaming gaps, etc.) will make the largest impact on both operating cost and pollution produced, by reducing the amount of whatever energy source you use to heat and cool your home.
Maintaining the appliances you have to ensure that they operate as efficiently as possible also reduces wasted energy and excess pollution and your bills. Have you flushed the water heater this year? Is the vent/chimney clean, have the burners been adjusted or maintained to burn clean?
In many (not all) cases, replacing a functioning appliance before it becomes non-economical to repair is contributing to pollution, since large parts of the appliance are not actually recycled and end up as trash.
If you improve the airsealing enough that you need one, a Heat or Energy recovery ventilator will save additional energy on heating or cooling fresh air, while also keeping your house healthy to live in.