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Indoor Air & Moisture Issues

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Indoor Air & Moisture Issues. Indoor Pollutants. Carbon monoxide (CO) Tobacco smoke Nitrogen oxides, hydrocarbon dust Volatile organic compounds (VOC) Radon Biological Particles ( bacteria, , viruses, dust mites, cockroaches, fungi, mold, raw sewage, rotting wood) Asbestos and Fiberglass

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Indoor Pollutants

Carbon monoxide (CO)

Tobacco smoke

Nitrogen oxides, hydrocarbon dust

Volatile organic compounds (VOC)


Biological Particles (bacteria, , viruses, dust mites, cockroaches, fungi, mold, raw sewage, rotting wood)

Asbestos and Fiberglass

Lead-based paints

Water vapor


Indoor Pollutants

How will you deal with these?

  • Lifestyle (pets outside, door mats, no shoes indoors, regular cleaning)
  • Careful product purchase decisions (low VOC)
  • Hard floor surfaces in lieu of carpeting
  • Sealed combustion appliances (furnace, fireplace)
  • House pressure balancing (jump ducts, transfer grills)
  • Moisture management (humidity control)
  • Ventilation
    • Whole house
    • Spot (bathrooms, kitchen, crawl spaces for radon)
  • Air filtration

Indoor Pollutants

How will you deal with these?

Air filtration


Indoor Pollutants

How will you deal with these?

Air filtration


Electronic air cleaner

Media air cleaner

4” Return grille media filter

Indoor Pollutants

How will you deal with these?

Air filtration


Indoor Pollutants

Efficiency at 0.3 Micron Particles








< 1%


media filter


media filter


air cleaner

  • Moisture is the number one pollutant in homes
    • Need to be aware of its sources
    • Basic knowledge of determining moisture levels
    • Solving moisture problems
dealing with moisture
Dealing With Moisture
  • Keep water out
    • Roof, plumbing, grading of ground…fix problems
  • Understand that moisture will get in
    • Ventilation is needed
  • Make sure moisture can get out
    • Material selection (vinyl wallpaper is a bad choice)

BPI Analyst Certification – Basic Principles of Energy

moisture movement through buildings
Moisture Movement Through Buildings
  • Moisture in buildings can be tracked to one or more of the following (in order of importance)
    • Liquid flow: Roof leaks, plumbing leaks, ground water…
    • Capillary seepage: Liquid water being pulled into a material or assembly
    • Air movement: Carrying water vapor into or out of a building and its cavities
    • Vapor diffusion: Vapor will move through solid objects depending on the object’s permeance and the vapor pressure
controlling moisture
Controlling Moisture …
  • 1 inch of rain on 1,000 sq. ft. roof = 623 gallons
  • High water table
  • Foundation plants
  • Leaking water spigot
moisture movement
Moisture Movement
  • Vapor pressure: Vapor pressure is created by different amounts of water vapor in two different air masses. Moves from high to low.
  • Relative humidity: The percentage of the maximum moisture that air can hold at a given temperature
    • The higher the temperature of the air, the more moisture it can hold

BPI Analyst Certification – Basic Principles of Energy

relative humidity
Relative Humidity
  • Key point: relative humidity (RH) changes as temperature changes
  • When cooled enough, air at 50% RH, for example, will hit 100% RH and the moisture in the air will condense on cool surfaces
    • In the winter, warm indoor air is forced out of a building
    • In the summer, hot humid air is pulled into an air conditioned space……. under this condition, there is a potential for MOLD.
moisture concepts
Moisture Concepts

Vapor pressure: Vapor pressure is created by different amounts of water vapor in two different air masses. Moves from high to low.

materials permeance

The ability of a material to restrict moisture flow is based on its “perm rating”

Materials with a perm rating of 1 or less are considered a “vapor retarder”


Thermal Barrier

Air Barrier

Unconditioned Air

Conditioned Air

structural design
Structural Design

Understand how design features can cause

weaknesses vapor barrier

  • How a building fits together can give you hints as to where there may be weaknesses
    • Shafts and Soffits (covered already)
    • Slab/Crawlspace/Basement
    • Framing
    • Porches/Garages
    • Bonus Rooms
    • Stairs
    • Split Levels
slab crawlspace basement

Trend to build or

retrofit to sealed


Main concern – vented crawlspace. If there is a building component (wall, shaft…) that is connected to a vented crawlspace and vented attic, high potential for problems.


Balloon framing: Found in older homes, may have stud walls that are two stories high and usually do not have top or bottom plates. This may result in the wall being open to the basements/crawlspaces and the attic.


Platform framing, each floor serves as a platform for the next floor. Has top and bottom plates.

porches garage

Issue with multi-story structures – Is there insulation and an air barrier at the rim joist that is hidden by the porch or garage?

moisture concepts1
Moisture Concepts

Diffusion vs. Air Movement

a primer on air flow
A Primer on Air Flow
  • For air to flow you need a hole and a pressure.
    • No hole, no flow
    • No pressure, no flow

1 cubic foot

1 cubic foot

If air is exhausted out of a building, outside air must replace it

If you pull air into a building, inside air must be forced out

cfm50 leakage tests
CFM50 Leakage Tests
  • Provides information on how leaky the house is.
    • Remember, how leaky, not how much leakage. Amount of air movement depends on pressure!
  • Post air sealing test can give valuable feedback on the success of your work.
  • Find where the holes are.
  • Predictions on the impact of work.
what does a cfm50 value tell you about the house
What does a CFM50 value tell you about the house?
  • CFM50 is like a 20 mile per hour wind blowing on all sides of the house.
    • From this value you can estimate the natural leakage of a home (see appendix E in the BD manual).
  • The CFM50 value can give you a good indication of the total size of all the holes in a home.
    • A tenth (remove the last digit) of the CFM50 number is about equal to the square inches of holes in the house. 1500 CFM50 = about 150 sq. inches of holes.
door closure
Door Closure

The average pressure that natural forces will put on a house are between 1.5 Pa (low desert) to 3 Pa (high country).

Pressure created by door closure can be many times higher than natural pressure.

The higher the pressures, the higher the infiltration rate.

Room pressure tests will show if there is a problem and help determine the solution.

BPI Analyst Certification – Pressure Diagnostics

doors closure



Doors Closure

100º outside

1000 CFM

supply flow

1000 CFM

return flow

Return side will go


Supply side will go


Close a door and block

the flow back to the


room pressure
Room Pressure


Room WRT outside, interior door of room you are testing closed, air handler on.

Test every room with a door and supply or return register.

BPI Analyst Certification – Pressure Diagnostics


The following video is a time lapse infrared of a home

under negative 3 Pa pressure for 40 minutes.

Note starting temperatures.






Temperatures after 40 minutes.

8 to 12 degree increase in surface temperatures.






Flex Duct

Jump Duct

Air Flow

Air Flow

Main Body of House

Inside Bedroom

Transfer Grill

House pressure balancing

avoid negative pressures in hot humid climates
Avoid negative pressuresin hot-humid climates

Infiltration of warm, humid air:

  • Into walls
  • Through chases
  • Into rooms


on cool surfaces



“Perfect House”

sources of home moisture
Sources of Home Moisture

An average family of four can generate over six gallons of moisture per day.

Shower (excludes towels & spillage) 1.0 pt / 10 minute shower

Clothes drying (vented indoors) 5.0 pt/ load

Combustion (unvented space heater) 7.6 pt/ gallon of kerosene

Cooking dinner (family of four) 1.2 pt(1.6 if gas cooking)

Floor mopping 1.5 pt/ 50 sq. ft.

Respiration (family of four) 0.4 pt/ hour

Desorption of materials: seasonal 6 to 17 pt/ day

New construction                             10+ pt/day

Ground moisture migration Up to 100 pt/day

1.0 pint can increase the RH by about 8% in a 1,500 sq. ft. single floor home.

sensible and latent heat
Sensible and Latent Heat
  • Sensible heat: The basic relationship between energy and temperature

Example: 1 Btu = 1° increase in temperature of 1 lb of water

sensible and latent heat1
Sensible and Latent Heat
  • Latent heat: The heat absorbed or released when a material changes phase between a solid and a liquid or between a liquid and a gas
air conditioning
  • Utilizes the properties of latent heat to move heat through a forced air distribution system
    • Cooling moves heat out of the house
    • Removes Latent heat first
    • Condenses water vapor back into liquid
  • Over-sizing has a negative effect on energy use, comfort, equipment life, and system costs:
    • Oversized systems run for a short period and do not reach steady state efficiency (think of city vs. highway driving). Impacts both cost and life.
    • Short run times mean that the air does not get mixed, causing hot spots.
    • Short run times will not remove humidity, increasing comfort problems.
    • Over sized equipment costs more to install.
steady state efficiencies

Steady State


Over sized system

replaces steady state

with start-up, lowering




Mechanical devices take time to go from start up to their peak, steady state efficiency. Some A/C units will take minutes. (SEER incorporates this start up time)

kitchen bath moisture control
Kitchen & Bath Moisture Control
  • Bathrooms, kitchens and utility areas should be vented to the “outside” – never to attic or crawl space.
  • Exhaust vents rarely discharge rated cfm
exhaust vent rules
Exhaust Vent Rules
  • Size correctly
  • 50 cfm bathroom venting standard (*20 cfm)
  • 100 cfm kitchen venting standard (*25 cfm)
  • 2. Exhaust to outdoor – never into attic
  • 3. Shortest vertical distance to outside or direct vent through wall
  • Control bathroom exhaust with timer or humidistat
  • Use aluminum piping without screws and taped joints

* If venting is continuous

high humidity poor no ventilation
High humidity –Poor/No Ventilation

Is the exhaust fan working properly?

Is the exhaust fan vented to the outside?

Is the fan operating long enough to remove moisture?

clothes dryer
Clothes Dryer

Dryer Rules:

  • Always vent to outside
  • With mobiles vent beyond the skirting
  • Do not vent into crawl spaces
  • If possible direct vent to outside using smooth metal piping
  • If elbows are needed, limit to two
  • Three basic types of ventilation:
    • Infiltration
    • Natural ventilation (opening windows)
    • Mechanical ventilation
      • Whole house
      • Spot
mechanical ventilation
Mechanical Ventilation
  • A fan that moves a measured amount of air into a house (supply), out of a house (exhaust) or both (balanced)
    • Ventilation systems must be selected to reduce the potential for causing problems (mold) in the building
      • Do not create positive (supply) pressures in extremely cold climates
      • Do not create negative (exhaust) pressures in hot/humid climates
do you need ventilation in an existing home
Do You Need Ventilation in an Existing Home?


  • First, does code apply? If so, follow code.
  • If not (vast majority of weatherization work)
    • What is in the home that needs to be vented (pollution sources)?
    • How much ventilation does house already have (fans and leakage)?
minimum building airflow ashrae 62 89

Less Energy Efficient

Poor Indoor Air Quality






Minimum Building Airflow(ASHRAE 62-89)
  • American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standard 62-89
    • 0.35 Natural Air Changes Per Hour (NACH)
    • 15 cfm per person (15 per bedroom + 15 for Master)

* which ever is highest

ach vs nach
  • Air Changes per Hour (ACH) – The volume of air in a house that is exchanged each hour with air from outside the house (ACH50 = measured at 50 Pa)
    • ACH50 = CFM50 x 60 min/hour ÷ house volume
    • Example: (single story, 3 bedroom home in Phoenix)
      • 1,500 sq ft home x 8 ft ceilings = 12,000 cu ft
      • Measured leakage: 1,500 cfm50
      • 1,500 CFM50 x 60 ÷ 12,000 cu ft = 7.5 ACH50
ach vs nach1

N = # stories x shielding x climate factor

Stories = 1 story: 1.0, 1.5 story: 0.89, 2 story: 0.81

Shielding = well shield: 1.2, normal: 1.0, exposed: 0.9

Climate factor for Phoenix = 20

  • Natural Air Changes per Hour (NACH) – A calculation of the “infiltration” rate of a home under “natural” conditions (Home Energy, “Infiltration: Just ACH50 divide by 20)
    • NACH = ACH50 ÷ N
    • Example:
      • 7.5 ACH50 ÷ (1 x 1.0 x 20) = 0.375
minimum building airflow bpi calculation method
Minimum Building Airflow(BPI Calculation Method)
  • 1,500 sf, 8 ft ceiling, single story, 3 bedroom home, Phoenix
    • Step 1 – 0.35 x volume / 60
      • 0.35 x 12,000 / 60 = 70 CFM
    • Step 2 - # occupants x 15 CFM/person
      • # occupants = # bedrooms + 1 = 3 + 1 = 4
      • 4 x 15CFM = 60 CFM
    • Step 3 – choose the largest ventilation number to calculate minimum air flow at 50 Pa
      • CFM50 = ventilation target x N*
      • 70 CFM50 x 22 = 1,540 CFM50

* Phoenix: N for single story = 22, for two story – 22 x 0.81 = 17.8



Ventilation (whole house)

Thermostats with internal switch

Motorized Damper


Ventilation (whole house)

  • 6” supply duct to return delivers about 40 - 60 cfm of ventilation (for 3 ton – 5 ton air handler)
health and safety
Health and Safety

Each individual organization needs to

establish its definition of remedied.

Health and safety should be #1 consideration when testing and repairing homes!

Never do anything to save energy that has a negative impact on health and safety.

All (existing and potential) health and safety issues should be remedied prior to, or in conjunction with, doing work.