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Humidity and an Indoor Moisture Inventory

Humidity and an Indoor Moisture Inventory

It is our core purpose at HypoAir to help you bring what’s best about outdoor air, indoors.  Replicating outdoor air indoors, though, isn’t always easy.  Sometimes outdoor air can be overwhelmingly humid, supporting all kinds of mold and bacterial growth on surfaces.  There are differing opinions on optimal indoor humidity: some sources say 30-50% while newer research indicates 40-60%.  Whichever advice you adopt, if your home humidity floats in the 40-50% range, you are doing well! 

Here’s what’s good about this particular range:

  • Better health: this encompasses so much:
    • better respiratory health due to proper humidity levels
    • less mold growth affects all areas of the body
    • bacterial and viral transmissions are suppressed
    • healthier skin and hair
  • Lower cooling costs
  • Fresher food

To measure humidity, sensors like these are cheap and easy to place around your home (this particular type have built-in batteries, but you should check the battery requirements of others before purchase). 

Now–what do I do if I’m below 30%?  Typically, low humidity (below 30%) occurs in winter months when we turn on indoor heat, making skin and nasal passages dry and irritated.  Humidifiers help by introducing moisture into the air.  You can place a portable humidifier in the most-used room during the day, and move it into your bedroom at night for more comfortable sleeping.   If you are not sensitive to fragrance, some humidifiers allow you to add a few drops of essential oils for a pleasant scent.  Whole-home humidifiers can also be installed in your HVAC system.  

It’s more common to be over 60% humidity.  Sometimes it is the outside climate coming inside through air leaks, and sometimes it’s a source of water inside the home that can be corrected to bring indoor humidity down.  Here is our Indoor Moisture Inventory which will walk you through the most common ways to reduce indoor humidity. 

Indoor Moisture Inventory

Air leaks:  Insulation and weatherstripping are boring but vital!!  I live in a home that was originally built in 1982.  Since the original build, the outdoor “porch” was closed in with no ducts for air conditioning and heating, a laundry room was added on, and a second story office was added over the porch with –yup–no air conditioning or heating.  Now, the porch-turned-“sunroom” is everyone’s favorite room because it has a long wall of windows showcasing the lake below.  Unfortunately, though, it’s one of the biggest sources of my moisture problems!   Some of the windows were drafty (you can do this candle or smoke test to find air leaks) and during storms, you could literally feel the wind coming around the windows into the wall.  All of the air leaks also cause humidity to come into my home.  What to do?  I had to ruthlessly find the air leaks and seal them. 

Windows: Now, I had recently (3 years ago) renovated the outside siding on the sunroom and made sure to seal it as much as possible with a vapor barrier, window sealing tape and caulk.  But, some of the drafts persisted.  I wanted to find a good indoor caulk that had low VOCs, because I would be doing the caulking during the winter when opening the windows to ventilate was not an option!  I found that a few caulks offer “Greenguard Gold” certification, which warrants that a product “has been tested and scientifically proven to have low chemical emissions”.  

Doors: Checking for drafts around my front and back doors revealed, indeed, they needed work.  Anywhere you can see daylight is number one priority, and even without daylight views, weatherstripping is a must.  

Other air leaks: Outlets and lightswitches on exterior walls are very likely to have air leaks.  You can seal these off with a pack of inexpensive gaskets like this.   Also check attic doors and can lights under attic space. 

Cookstove ventilation:  It’s so important to have a properly-sized, working vent hood for your cooktop and microwave, for several reasons.  Cooking releases a lot of moisture into the air, which increases humidity in your home.  Also, the other gasses released, such as cooking odors and VOCs from burning gas fuel, should be vented outdoors too.  Now, when you are venting from the house, you are actually pulling conditioned air from your home and exhausting it outside, creating a negative pressure (causing unconditioned air to leak into the house).   When it’s super-humid outside, guess what–even more humidity comes in.  With new-build construction and renovation, vent hoods with fresh-air intake can be installed that pull fresh air from the outside and are drawn right back out through the exhaust, mixing the cooking gasses with the fresh air. (Check out this smoke test on a new vent hood!)  No negative pressure inside the house and no increased air leaks around doors and windows.  If you have an existing vent, it’s usually easy to see if vapors are being pulled through the vent, or going right past it onto your cabinets and ceiling.   When I moved into my house, the microwave/hood combo above the stovetop was not being vented outdoors, so I changed that (microwaves typically have 2 vent options: to vent back into the room through the front, or to vent outdoors through the top or back).  Sadly, venting outdoors still did not pull the gasses from the cooktop below because the fan was not powerful enough.  Here is a great article on how to calculate the CFM (cubic feet per minute) needed to properly vent the stove.  For my electric stove with a wall-mount hood, which was 2.5 feet wide, I multiplied that by 100 to get the recommended cfm of 250.  I had to add 25 cfm for every turn of the duct in the exhaust path (plus 50 for mine, for a total of 300), and then compare it to the cfm needed for the size of my kitchen (704 ft3 divided by 4 = 176 cfm minimum ).  Turns out the microwave/hood combo unit I have is only 220 cfm, which confirmed my suspicions (too small for the stovetop!).  Time to upgrade to a dedicated wall vent hood…

Dryer ventilation: Do this test: bring your humidity monitor (yes, you really need one!) into the laundry room before drying a load of laundry, note the humidity, and then note the humidity again towards the end of the cycle or immediately after drying the load.  Did it increase more than 5%?  If so, check the vent hose for excessive lint, kinks or holes in it (sometimes they become disconnected completely!)  Rising humidity in the laundry room eventually equals rising humidity in the house.  If your vent and lint screen are clean and connected, and you still have higher humidity in your laundry room, you can at least mitigate mold growth by plugging in a Mold Guard in the room to run full-time. 

Bathroom ventilation: Do you have a mold problem in your bathroom?  This is an ideal place to find mold–especially in the shower or bathtub, which can stay perpetually wet depending on the humidity and ventilation.  Full bathrooms (with showers or bathtubs) need adequate ventilation.  You can use your humidity monitor again to check humidity levels before and then 30 minutes after showering and using the exhaust fan.  They should be nearly the same: if not, let’s check some common issues: 

  • It turns out that we should use the bathroom fan way longer than most of us do: not only during bathing, but also for 20-30 minutes afterwards!  On a cold day, I really don’t want to use the bathroom fan during a shower.  It sucks out all that wonderful moist heat….but, it really should be switched on if you want to mitigate mold in your home.  You can make a compromise–just don’t let that moist air into the rest of your house.  After bathing and drying off, keep the door closed, turn the fan on and open the bathroom window for 30 minutes.  The fan will have fresh air to draw in and also exhaust all the moist air. 
  • Sizing: the general rule is that bathroom vents should be minimum 50 cfm (cubic feet per minute), and at least 1 cfm per square foot of bathroom space.  An 8x10’ bathroom, for example, should have an 80 cfm exhaust fan.
  • Where to vent:  Bathroom vents must terminate on the outside of the house.  They may pass through ceiling or attic space, but you don’t want all that moist air ending up in the attic!  Do check that each vent goes outside and is actually working (lifting the vent flap with air expelled) (and for more tips on where to vent when installing a new fan, check this page). 

Basements: Ahh, that extra storage and living space seems to come at a high cost sometimes.  If your basement is not adequately moisture-proofed from the surrounding soil, or drained, the humidity can rise into the rest of the house and cause mold issues everywhere.  It’s best to leave a humidity sensor in this space and monitor it frequently.  Above 60% definitely needs dehumidification.  This permanent system reverses the "stack effect" in your house and forces air to exhaust from your basement, which is a great way to keep the humidity down.  The built-in humidistat causes the fan to come on automatically whenever humidity goes over a certain level.  The next option is to place a dehumidifier in the space with a moveable drain (such as into a shower or laundry drain) or ask a plumber for permanent drain options.  Use a HypoAir unit like the Air Angel in the area, and a separate HEPA filter will also help to remove mold spores.  Once you smell mustiness in the air, the mold has already started, so don’t delay on this one!  Check furnishings, walls, carpets and ceilings for signs of mold or mildew and try to determine the source of the moisture, whether it’s a specific “hole in the wall” or maybe something like lack of gutters on an upper story that causes water to pour off the roof and build up behind the wall.  If your foundation has an inadequate moisture barrier, it allows water from the soil to permeate the concrete.  There are companies that specialize in moisture-proofing your foundation or crawlspace, but be sure to get several quotes to assess a reasonable cost. 

Drain Vents:  I wasn’t aware of this problem until several years ago, when a friend who is a professional carpenter started to tell me about his problem with mold around sink drains.   For some reason I always thought that black mold under a sink stopper was normal, but no—it shouldn’t be!  Sink, shower and toilet drains must be properly vented for several reasons.  First of all, it helps the drain operate properly because the incoming water does not have to “push” the air bubble on the other side of the p-trap to drain; it simply drains by gravity and air pressure is equalized through the vent.  This venting is accomplished naturally if building codes and/or good design are followed…but sometimes older and new construction homes have neither!  The second reason that drains need proper venting, is to allow the outside vent to relieve nasty sewer gasses in an unobstructive fashion, instead of allowing these gasses to push on the p-trap and go back into the room, causing smells and mold.  If you have sluggish drain(s) that do not resolve despite cleaning, sewer smells and/or mold buildup in the drain, find a good plumber who knows about proper venting, so that he can evaluate your home’s vents and suggest cost-effective improvements.  

Miscellaneous leaks:  If you don’t have humidity sensors in each space, here is where you can do a walkabout with a single humidity sensor to find more hidden sources of moisture.  Take a reading in your main living space, then leave the sensor in each room outside of it for a few minutes, to acclimate.  Then take a reading in the outside rooms, and do closer inspections if the humidity is appreciably higher in a certain room.  Open cabinets, check under sink drains, pull back curtains, open closet doors, check walls and carpeting behind furniture…so many drains run through the walls of our homes, and are never seen or considered til they leak!   This is where your nose, and the sensor, can tell you to look until you find the source.  Then enlist help to get the problem fixed (check out these tips on replacement and repainting of damaged walls here).  If possible, avoid living in that space until the leak is stopped and any mold is cleaned up.  If it’s necessary to use the room, you can add a portable dehumidifier, HypoAir product like an Air Angel, and a separate HEPA filter to make the air cleaner until the mold source is eliminated.