GREEN BUILDING: 'Blower door' test determines home's air leakage level
Question: My home has drafts and moisture leakage. What should I do?
Answer: The first thing to do is establish how big a problem you have. All buildings have a certain amount of leakage and in fact must have a certain amount of ventilation for healthy human living. Homes do not need ventilation, but people do.
The American Society of Heating, Refrigeration and Air Conditioning Engineers provides a minimum ventilation requirement, the latest of which divides the total conditioned floor space (square feet) by 100 and then adds the sum of 7.5 times the number of bedrooms plus one. This number represents the cubic feet per minute of ventilation required. More wastes energy less, and mechanical ventilation is required.
Natural air infiltration is variable and difficult to measure. The only true way of understanding where your infiltration leakage is by using a blower door tester. A blower door provides controlled pressure and airflow measurements between the inside and outside of your home.
The blower door is placed in one of the outer doors while all other outer doors and windows are closed; internal doors are left open. Chimneys and some other appliances also have to be closed. The blower door depressurizes the home, where replacement air can only enter through envelope gaps and holes.
The blower doors manometer measurement unit measures pressure difference in Pascal and airflow in cubic feet per minute (CFM). Knowing the amount of air that's leaking through the building determines the size of the effective hole in the envelope and how big a problem you have.
An average 2,000- to 2,500-square-foot home might show leakage of 3,500CFM on the manometer, a leaky home greater than 5,000CFM and a tight home less than 1,000CFM. Another equation converts the 3,500CFM into effective leakage area, which in this case is a 14 x 14 window. This effective window is open 24 hours a day, 365 days a year - so just imagine how much energy and money you are losing.
There are a number of ways to use the blower door to find leaks, the simplest being draft detection around doors and windows, electrical sockets and where pipes leave and enter different conditioned and unconditioned spaces. Other common leaky places are between the basement/crawlspace walls and the main floor and wall perimeter framing. Another and more prone to leakage area is an unconditioned attic, again at the perimeter walls and roof joist framing, any trap doors, chimneys, wiring and piping conduit and any recessed lighting fixtures. All these connections should be air-sealed during construction with caulk or foam. Unfortunately, in many cases they are not.
A further major source of leakage is a forced-air heating and cooling duct system. Typical energy loss via leaky ducts is between 10 percent and 30 percent. Leaky ducts can cause combustion back-drafting and pilot light blowouts, creating a very dangerous and explosive situation.
The important aspect of leakage testing during an energy audit is obtaining informed results that should include, but are not be limited to:
A measurement of the homes air-tightness and effective hole size
A comparison to documented industry standards
An evaluation for mechanical ventilation
An evaluation of combustion equipment safety
Recommendations for leakage sealing projects and their respective ROI.
More information can be found at www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_sealing.
Paul Scrivens can be contacted through www.greenhomeenergyadvisors.com. His blog is at www.greenhomeenergyaz.com.