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VENTILATION in BUILDINGS
AIR BYPASS LEAKS
AIR LEAK DETECTION TOOLS
AIR LEAK SEALING PROCEDURE
AIR POLLUTANTS, COMMON INDOOR
AIR SEALING STRATEGIES
ROOF ICE DAM LEAKS
BASEMENT CEILING VAPOR BARRIER
BASEMENT HEAT LOSS
BASEMENT LEAKS, INSPECT FOR
BLOWER DOORS & AIR INFILTRATION
BRICK WALL DRAINAGE WEEP HOLES
CATHEDRAL CEILING VENTILATION
CEILINGS, DROP or SUSPENDED PANEL
COMBUSTION AIR for TIGHT buildings
COOLING LOAD REDUCTION by ROOF VENTS
CONDENSATION on WINDOWS & SKYLIGHTS
DEW POINT CALCULATION for WALLS
FIREPLACES & HEARTHS
FLAT ROOF MOISTURE & CONDENSATION
GREEN BUILDING CONSTRUCTION
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT RECOVERY VENTILATORS
HOT ROOF DESIGNS: Un-Vented Roof Solutions
HOUSEWRAP AIR & VAPOR BARRIERS
HOUSE DOCTOR, how-to be
HUMIDITY LEVEL TARGET
ROOF ICE DAM LEAKS
INDOOR AIR HAZARDS TABLE
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INDOOR AIR QUALITY IMPROVEMENT GUIDE
Insulation Air & Heat Leaks
INSULATION INSPECTION & IMPROVEMENT
INSULATION R-Values & Properties
LOG HOME GUIDE
MOISTURE CONTROL in BUILDINGS
MICROWAVE OVEN VENT INSTALL
ODORS GASES SMELLS, DIAGNOSIS & CURE
ROOF VENTILATION SPECIFICATIONS
ROOF ICE DAM LEAKS
SHEATHING, FOIL FACED - VENTS
STAIN DIAGNOSIS on BUILDING INTERIORS
STUCCO WALL METHODS & INSTALLATION
SWEATING (CONDENSATION) on PIPES, TANKS
THERMAL MASS in buildings
THERMAL TRACKING Indicates Heat Loss
VAPOR BARRIERS & AIR SEALING at BAND JOISTS
VAPOR BARRIERS & HOUSEWRAP
VAPOR CONDENSATION & BUILDING SHEATHING
VENTILATION in BUILDINGS
WIND WASHING INSULATION At EAVES
WINDOWS & DOORS
How to diagnose & fix exhaust fan problems: this article explains using exhaust fan ventilation systems to improve indoor air quality in homes. We include exhaust vent system troubleshooting checks: Here we provide air handler unit or blower assembly troubleshooting by expanded annotated information from the US EPA who provided suggestions for investigating the air handling unit during an indoor air quality investigation.
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This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Also see our complete VENTILATION, WHOLE HOUSE STRATEGIES and detailed article links listed at Related Topics .
As detailed in Best Practices Guide to Residential Construction:
Exhaust-only ventilation is the most common approach, due to its simplicity and use of familiar components such as bathroom fans. However, unless houses are built very tight, there is little control over where fresh air enters the building.
Also, building depressurization can be a problem, particularly with high-capacity fans. In addition to the increased potential for backdrafting, a depressurized house tends to draw more soil gases, including radon if it is present. And in hot, humid climates, moist air infiltrating through exterior walls can condense on interior finishes such as the back face of vinyl wallpaper that is chilled by air conditioning.
The biggest drawback to exhaust-only ventilation is that there is little control over distribution of the incoming air. Makeup air will come via the path of least resistance. In a leaky house, this might be a window or drop ceiling in the bathroom with the exhaust fan, leaving the rest of the house un served by the ventilation system. For this reason, single-port exhaust-only ventilation works well only in relatively small, tight houses.
This type of system uses a more powerful exhaust fan that is remotely mounted, typically in the attic or basement. See the figure at left for details of a multi-port whole house exhaust fan vent system).
A multiport exhaust system improves air distribution by picking up air from bathrooms and main living areas. These are often used in conjunction with passive air inlets.
Exhaust-only systems are best used in homes with electric heating or sealed-combustion appliances where backdrafting is not a concern.
Illustration Source: Recommended Ventilation Strategies for Energy-Efficient Production Homes, 1998, by Judy A. Roberson, et al., Lawrence Berkeley National Laboratory, appearing in the text cited above.
The multiport house exhaust fan system is ducted to exhaust grilles in bathrooms, laundries, and other wet areas, and sometimes to a centrally located pickup point in the main living space. A room with no outside walls would also benefit from a pickup point.
Systems typically run on a low background speed with timer switches in bathrooms for higher-powered spot ventilation. If installed correctly, these systems are very quiet and provide good distribution of ventilation.
Multiport exhaust systems may incorporate passive air inlets (see description above) that install either in windows or through the wall, providing some control over supply air. The inlets, typically three or four for a small house, go in bedrooms, main living areas, and other occupied rooms, such as dens or home offices. Inlets should be placed high on the wall away from beds, chairs, or other places where drafts might cause discomfort. Placement near a window is preferred.
Because these systems use more powerful fans that depressurize the house, they should not be used in houses with fireplaces or atmospherically vented combustion appliances. They are also not recommended in hot climates, since hot, moist exterior air may be drawn into walls and condense behind interior surfaces chilled from air conditioning.
Packaged multiport house exhaust venting systems are available from American Aldes, Fantech, and a few other few manufacturers (see Resources, page 297 in Best Practices Guide to Residential Construction)
This variation on exhaust-only ventilation passes the exhaust air through a heat-pump water heater, reclaiming heat from the outgoing air stream. Some systems can be reversed in summer, functioning as a supply ventilation system while cooling and dehumidifying the incoming air. A packaged heat-pump ventilating system is available from Therma-Stor.
-- Adapted with permission from Best Practices Guide to Residential Construction.
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