Energy raters and auditors at HERS, Inc. are skilled in "whole house diagnostics and repair" and understand the "house as a system"- the interrelationship of duct leakage, house pressure, duct pressures, exhaust fans, back drafting, equipment efficiency, insulation, ventilation, windows, air tightness, moisture, and health and safety.

This is critical because the most common problems associated with discomfort, poor performance and high bills start with poorly  sealed supply and return ducts and air leakage of the envelope.  Address these, then additional insulation, windows and finally, after the load has been reduced, heating and air conditioning equipment sized to the load of the house.

The “House as a System”

A house is not static. It is more a complex organism of parts and pressure at odds with themselves and rarely able to maintain equilibrium. The struggle is driven by improperly sized and poorly installed heating and air conditioning systems that induce positive pressures in some zones and negative pressures in others while clothes dryers, vent-a-hoods, power roof vents, range exhausts and bathroom vent fans actively exhaust air. Meanwhile furnace and water heater vent pipes and the house itself behave like chimneys drawing outside air in through penetrations in the crawl space and the building envelope and drive conditioned air up and out through partition walls, holes in the attic, by-passes, cracks, chases and hundreds of both accidental and intentional holes and penetrations in the ceiling, walls and floor from gas pipes, electric wires, cable, telephone lines, and poorly fitting joints.

Because the house is an interactive system, when one thing changes, something else is effected. For instance, simply plugging holes and sealing ducts can sometimes create worse problems than it solves. Improper air sealing can create unbalanced air pressures in the house when the HVAC system is running. This can result in fireplaces back-drafting, elevated radon levels, moisture problems, and the list goes on.

Positive pressures zones in the house force conditioned air out of the house (“exfiltration”) and we lose the air we just paid to heat or cool. Negative pressure zones do the opposite. They draw unconditioned outside air into the house along with contaminates like radon, mold and mildew from a crawl space or termiticide from under a slab, or flue gases from a fireplace or gas water heater inside the conditioned space.

In the “house as a system” approach, there are three interdependent components that must be addressed if a house is to perform to its full potential: the building envelope the mechanical systems and the occupant.

Building envelope

In addressing the "building envelope," it is important to first define where the air barrier will separate the "conditioned" space inside the house from the "unconditioned" world beyond. A proper air barrier is continuous and is typically defined by walls, ceiling, floor, doors and widows, but the unique geometry of many buildings can make defining the envelope more complex.

For a balance between energy efficiency and health & safety, the building envelope should be sealed to about .35 natural air changes per hour so that the air in the house is naturally replaced buy outside air about every three hours. Tighter is better if controlled, mechanical ventilation is provided.

How tight is your house? You can’t tell without testing. How do you know when you’ve reached your target as you seal the house? You don’t know without testing.

Mechanical systems

The mechanical systems include furnaces, air conditioners, water heaters, vent-hood fans, bathroom vent fans, clothes dryers and any other mechanical devices that moves air and induces pressures within the house.

If combustion devices such as gas water heaters, gas furnaces or fireplaces are located inside the conditioned envelop of the house, can they vent or draft properly when all of the mechanical devices are operating that exhaust air out of the house (clothes dryer, vent hoods on high speed, bathroom vent fans, etc.)? Add to this any duct leakage to the outside when the central heating fan is running. Does the fireplace draft? Can you smell the attic or mildew from the crawl space? Put a smoking stick of incense at the top of the water heater or furnace by the flue-stack. Does the smoke go up the flue or back into the house while all those exhaust devices are working? The smoke should be going up the flue. That’s the direction your flue gases will be traveling when the water heater fires. If not, you could have a problem.

Occupant

Third is the occupant who closes doors, opens windows, sets the thermostat, fails to change furnace filters, and, in dozens of ways, unknowingly prevents the building "system" from performing at peak efficiency. Occupants need to understand how their house works “as a system.

Qualified contractors

Following whole house diagnostics, qualified contractors are often needed to correct problems and improve performance. This means understanding performance specification and, often, having  the diagnostic tools like blower doors, Duct Blasters®, digital pressure gauges, pressure pans and carbon monoxide testers.  These tools help the contractors pinpoint and repair problems and know when they’ve reached their target. For more information, see Qualified Contractors.