The draft hood water heater was inefficient and vented through the masonry chimney, so it also was removed. A low-mass condensing boiler was chosen to provide space heat and hot water, and connected to the air handlers described below. A well-insulated storage tank provides domestic hot water. Three zones are tapped from the boiler, one for each air handler and one for the hot water storage tank.

One air handler located in the basement serves the basement and first floor. One central return for that air handler is located on the floor of the first floor central hallway. The other air handler, located on the conditioned attic level, serves the second floor and the attic. One return is on the ceiling of the second floor hallway and another is in the attic. Transfer grilles over the doors to the bedrooms on the second floor prevent room pressurization due to inadequate return paths. Each air handler is equipped with a MERV 13, 5-inch pleated media filter.

Providing air change with a controlled mechanical ventilation system is important for interior moisture control and for good indoor air quality. There is an outside air duct to the return of each air handler with a manual damper, which provides ventilation during air handler run time. Four individual exhaust fans (one in each bath and powder room) and a ducted exhaust over the gas range provide source control of pollutants.

The actual equipment installed includes the following:

• 80,000 Btu/h input 92% AFUE condensing gas modulating low-mass boiler (25,000 to 74,000 Btu/h nominal output);
• variable speed/ECM (electronically commutated motor) air handler (x2);
• 2.5-ton 14 seasonal energy efficiency ratio (SEER) outdoor condenser unit with R-410a refrigerant (upstairs air handler only);
• MERV 13 pleated media (5-in. thick) filters on air handlers;
• low-sone 50 cfm bathroom exhaust fans;
• and 600 cfm exhaust range.