- humidity control -

moisture is not a pollutant. but it enables and introduces various pollutants.


when relative humidity (RH) is low, it invites bacteria and viruses. dry air increases allergy and asthma symptoms and sparks that annoying static shock when you touch a doorknob.

when humidity is too high, another group of troublemakers who show up. To avoid trouble, humidity must be maintained between 45% and 55%.

normally, high humidity is a challenge in the summer, while low humidity is more common in the winter.

dry conditions are seldom a problem in newer energy efficient homes. being more airtight, the indoor humidity tends to behave pretty well. if a homeowner is suffering from a dry house at 30% RH or lower, we’ve found its likely a very leaky house or has leaky ducts.


the usual problem in newer homes is too much humidity in the summer. that’s when humidity is likely to move above the 55% mark, which invites dust mites and mold.

in addition to the “fun guys” and mites there’s more fallout. High humidity also increases the evaporation or “off gassing” of volatile chemicals into the air we breathe. studies show for about every 10% elevation in humidity off gassing of volatile compounds increases as much as 50%. so materials, like upholstery fabric, carpet, draperies, adhesives, paint, and stain that contain volatiles will emit more pollutants. formaldehyde reacts the same way.

of course humidity also compromises comfort. remember the saying, “it's not the heat, it’s the humidity.”

our cooling systems control both temperature and humidity. but, there are moisture sources inside a home that can overwhelm these systems. those moisture loads need to be addressed where they are produced. this is called source control.

there are two activities in a home that produce a lot of moisture (1)showers/baths (2) cooking. in both cases, we use exhaust fans to remove unwanted moisture at the source.

at 340 fairfax, we selected Panasonic exhaust fans for all our bathrooms. since the master shower has multiple spray heads, we needed a monster-sized fan to remove unwanted moisture in short order. plus, Sandee hates a fogging mirror! so sizing the fan right makes that problem disappear.

we installed a Panasonic Whisper Green Select fan that will remove 150 cubic feet of wet air per minute. in layman’s terms, that’s over 1,100 gallons a minute.


sometimes we forget to turn on the fan. no worries - the Whisper Green has a condensation sensor that detects high humidity and automatically turns on the fan for us. it also keeps the fan running about 20-minute after we shut it off. that takes care of lingering humidity after we leave.

in our other bathrooms we used a Panasonic Whisper Recessed fan. the model comes disguised as an attractive recessed light. it exhausts roughly 80 cubic feet of stale air per minute. that’s about 600 gallons! the light is a high quality LED that uses only 14 watts. it's also dimmable which makes a nice night light.

all Panasonic fans are Energy Star rated, extremely quiet and to our chagrin 8 to 10 times more expensive than a typical fan we see used in many custom homes. this sounds like we’ve solved all the problems with removing unwanted humidity.

maybe not…. in building for performance, we quickly learned never to expect what we don’t inspect and test. so we always have a 3rd party test the fans to make sure they are working right.


by the way, a 3rd party means somebody besides the person who sold or installed the fan. in other words, we don’t let folks grade their own paper.


well wouldn’t you know it? two of our high quality Panasonic fans were not working. they made noise and gave the impression they were working. but they just weren’t exhausting much air. an investigation revealed the dampers were stuck and would not open. after repairs were made, we are in business and ready for hot showers.


cooking creates another big source of unwanted moisture, particularly when using gas. there is a lot more fall out from having a “fire in the cave”.

of course moisture is produced when we cook green beans and cabbage. but there’s also moisture being generated by the gas flame itself. it’s just a natural byproduct of the combustion process. the more we cook, the more moisture builds up in the house.

a hood over the cooktop is used to capture and contain this unwanted moisture along with other other stinky stuff that comes from burning gas. (our building science specialist calls it affluent.)


the hood’s job is to capture as much of this pollution as possible. after the hood captures and contains the stinky stuff, a fan exhausts it to the outside.


some hoods simply pull the stinky stuff off the cooktop, drawing it across a filter and blow it right back into the house. se’ve heard this setup is called “A Lady Clairol” hood. that’s because the catfish grease along with other “affluent” blows directly back into the house right into your hair.

Sandee and I are in full agreement that all pollutants coming off any cooktop should always be vented to the exterior. house vented hoods may be cheaper, but they can also damage your family’s health.

ideally, we want a capture 100% of the pollutants coming off the stove. we don’t want any spilling into the living space. in a substantially airtight house, those pollutants will be trapped inside for a long time.

our engineer tells us the driving factors for capture efficiency are (1) geometry of the hood, (2) distance between the hood and the cooktop surface, (3) exhaust flow from the hood. we just scratched our heads and said, “tell us what we need”.


we installed a 40-inch hood approximately 30 inches off the stovetop. the exhaust is vented up and out the roof. the hood was tested and verified by a 3rd party it was removing 350 cubic feet per minute. that’s about 2,600 gallons of air being pulled out in a minute. that should do it!

in the wintertime, most families produce sufficient moisture with lifestyle activities to maintain a desirable humidity level. but since there are only two of us, we know we will need to add humidity.

experience has shown us that a steam humidifier is the best choice. a steamer works much like boiling pot of water on the stove. It creates steam, which is injected into the duct system.


the duct system pushes the humidity throughout the house. the system is totally automatic. we set our desired humidity from the touchscreen control in the living room or our smart phones. when it reaches our set point, the system shuts off.