Use safe and efficient combustion equipment

Sealed combustionCombustion system for space heating or water heating in which outside combustion air is fed directly into the combustion chamber and flue gasses are exhausted directly outside. furnaces and water heaters prevent backdraftingIndoor air quality problem in which potentially dangerous combustion gases escape into the house instead of going up the chimney.
In a tight house, the negative pressure from kitchen and bath fans and other ventilation equipment can pull carbon monoxide and other exhaust gases into living spaces. Carbon monoxide is deadly. In a sealed combustion appliance, the combustion chamber is completely segregated from inside air. These appliances are safer, and tend to be more efficient.

Green Points

LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. : Up to 3 points based on boiler or furnace efficiency rating (EA 6).

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. /ICC-700: Up to 17 points for superior system efficiency (703.4.2).

Learn more in the Green Building Encyclopedia:

MECHANICAL SYSTEMS OVERVIEW
HEATING OPTIONS
WATER HEATING

From the Green Primer

Is there such a thing as "too tight" or "too much" insulation?