Moisture Generated in the House – Moisture can come from many sources – people, pets, cooking, showering, fish tanks, drying cloths etc. etc. were air born moisture can be produced. All this moisture which is captured in the air as humidity should be directed outside, if not, then there is a real possibility that this high level of humidity can condense on cold surfaces such as windows, behind cold toilet tanks, on cold water pipes or cold surfaces such as exterior facing walls and possibly produce condensation or water and in the long term it may produce mold and damage building components. Here are two detailed publications which help explain in more detail NRC Moisture Problems and – CMHC Moisture and Air a Householder’s Guide.

Controlling the Humidity – If Humidity Generated in the House, is too high you may produce moisture related problems like mold, musty smells and or water damage, too low and you may feel dry throat, breathing problems, static shocks etc. In New Construction – Homes are even more susceptible to moisture, due to the amount of water used in construction materials which will evaporate over the first few years – can damage wood floors, cabinets and produce very high levels of moisture in basements behind insulation and on cold water pipes. HRV’s Heat Recovery Ventilators are also being installed in many of the newer homes to help reduce the humidity/moisture levels. In some cases Dehumidifiers may be required in basements.

Where do you Ventilate:

  1. Washrooms – Fans in washrooms should always be left on for approx 25-30 minutes especially after showers or the very least a window should be left open to help draw that moist air outside. You may want to provide a timer for the fan. I find timers to be more useful since it’s easy to push a button and walk away. Some people feel connecting the fan switch to the light switch is an option. Personally I don’t like this since most people will turn off the light switch when they finish in the washroom, however you may still need more time to reduce the humidity level in the washroom. For more info click the following links; HVI Washroom Fan Guide, CMHC Bath and Kitchen Fan Guide and Choosing an Energy Efficient Fan.
  2. Kitchens – Range Hoods should also be used during and after cooking. Some earlier construction used flow through range hoods which only captures the grease and not the humidity. Ideally range hoods should vent DIRECTLY outside. For more info click the following links; HVI Kitchen Range Hood Guide and Choosing an Energy Efficient Fan.
  3. Laundry Rooms/Dryers – If you have a laundry room with a ceiling fan, you should be running this fan during the drying cycles. Also, make sure your dryer vent hose is connected directly to the outside and the hose itself is not damaged, leaking moist air into the house. I would also make sure the dryer vent hose is of the flexible metal type, see image to the right. And make sure you have the hose cleaned regularly of lint, lint can be combustible (catches on fire).
  4. Cold Cellars (Cantina) – Basement cold cellars will typically have a window or a vent hole – this is used to allow fresh air into the cold cellar to help reduce the humidity level, which can condense to free flowing water/moisture when the temperature starts to drop. Don’t block these holes or you may get musty smells and or water damage, such as mold.
  5. Basements – May require a Dehumidifier which can help reduce the moisture levels. You may also want to insulate any exposed cold water pipes, warm moist air can condense on the pipes and drip water, see picture to the right.
  6. Attic – Most attic’s will have roof venting and or soffit venting, some will have turbines and some will have fan’s inside the attic which will have either a manual switch or controlled by humidity levels. Attic ventilation or venting is required to reduce the possibility of humidity condensing on the attic walls causing water related damages such as Attic Mold. Ventilating the attic can also have other benefits read further…HVI Attic Ventilation.
Humidifier - Whole House Unit, attached to furnace

Older Homes – If your home is older, with old windows and low insulation in the attic then you may be losing conditioned air/humidity and a humidifier may make sense. If your planning on upgrading the windows, adding attic insulation and or updating insulation strips around exterior doors…making your home more tightly sealed, then you may not need a humidifier.

One Last Word – Before you run out and have a humidifier installed on the furnace plenum – Consider living in the house for a winter season, making sure you use your fans properly, read the “where to ventilate” info as stated above, and then see if your humidity level is low causing dry air, dry throats etc. Still not sure then have a professional further evaluate your home and living conditions.

Window - Mold/Mildew at bottom corner
Heat Recovery Ventilator (HRV)
Fan - Bathrooms
RangeHood - Kitchen
Insulating a cold water pipe

FYI – have you noticed a switch directly above the furnace thermostat, usually located on the main floor family room, and when you turn it on nothing happens, well the next time you turn it on see if the upstairs bathroom fan turns on. This is called a Ventilation Fan Switch and what it does is it controls the upstairs bathroom fan so when the hot moist air rises the fan can help suck it outside. It should be a three-way switch which means the fan can be controlled by the upstairs switch and or at the switch above the furnace thermostat. Fell free to use it on those cold days when you don’t want to open the window but make sure the bathroom door is open.

Humidifiers (ONLY USED DURING THE WINTER) – Humidifiers are used to add moisture to the air. In the old days homes were not as well insulated as they are today (approx 20-30 years ago), therefore air would easily flow through the house and take out the humidity, remember humidity is not always a bad thing in the house, when controlled properly. That is why you may see humidifiers attached directly to the furnace plenum.

The lack of humidity may produce dry throats, static electricity and poor living and health conditions. However, the humidifiers that are attached to the furnace may not be used properly, meaning, set to a high number and forgotten…this can lead to a large amount of moisture in the house or mold build up inside the humidifier (depending on the type of unit you have). I recommend to use a lower setting (the control panel usually located above or near the humidifier) and monitor over several days to see if too much moisture is added. One way to tell, is to see if there is moisture or water condensing on the windows, (make sure the condensation in the window isn’t because somebody just took a shower and the didn’t use the fan) that may indicate to much moisture, then lower the setting!. Today most people who need humidification, such as for children, will purchase a portable humidifier…just a thought!