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Whole House Humidification

Comfort - Whole House Humidification Need not Be a Mystery

Spending as little as fifteen minutes with your Installer discussing proper humidifier operation and maintenance can keep your home and family feeling comfortable all winter long.

Humidifiers are for the most part a very misunderstood add-on to a home comfort system. Yet, humidifiers can make the difference between feeling comfortable or miserably uncomfortable.

Let's begin with the controller. What is a controller? The controller is the part that informs the humidifier what the conditions are in the space and tells the humidifier to operate or shut down. The controller is called a "humidistat" and is typically located mounted on the side of the return air duct with the sensing part inside the duct or they can be found in a central location within the home, such as beside the thermostat. Either location may be correct if mounted properly and is able to sense average conditions within the whole house and not be affected by localized rising and falling of humidity levels.

For example, do not locate a humidistat near a main bathroom where, when every time someone uses water the moisture may mask the actual whole house condition. Further, do not mount the humidistat on a return air duct that has an outdoor air intake directly above it, as this will in most cases sense a low humidity level telling the humidifier to run. A condition of too much humidity can be just as harmful to you and your family as too little humidity. Mold, mildew, slime are all indoor air quality problems to avoid. But, maintaining that balance of not too little and not too much humidity can leave you feeling comfortable all winter.

Many homeowners do not operate their home comfort systems blower (fan) continuously for fear of higher energy use. Maybe, but we need to look at the benefits and the bigger picture, increased comfort. If moisture is required for comfort, how can that comfort level be achieved when the home comfort system is not operating all the time? With the blower off there is no way in which to distribute the conditioned air to those rooms within the home.

In addition, lets say that a family gathering is planned and that 15-20 relatives are coming for supper. This can be certainly enough of an increase in moisture levels to likely tip the balance from just right to, "Noah get the ark", as water streams from the windows. With continuous blower operation there is constant airflow that can minimize this short-term condition. Will this avoid problems, not always but it does help. In addition, if your homes comfort system is fitted with an outdoor air duct, fresh dry ventilated air will be drawn in as required.

Table 1 - Recommended Indoor Humidity Levels

Outside Temperature

Relative Humidity

4.4C (+40F)


-1.1C (+30F)


-6.6C (+20F)


-12.2C (+10F)


-17.7C (0F)


-23.3C (-10F)


-28.8C (-20F)


The most misunderstood is relative humidity. What relative humidity setting do I use and how often do I have to adjust that setting? (See Table 1) Let me try to explain relative humidity this way. As air becomes cooler, its capacity to hold moisture decreases. Therefore, when outdoor temperatures fall, relative humidity will fall and the setting on the controller will have to be adjusted lower, even though more humidity would improve comfort.

Here again we need to strive for a balance. Our goal is to maintain the highest level of comfort by maintaining the relative humidity as high as possible without causing condensation on windows, or driving moisture into the walls through holes in the building envelope potentially causing other problems such as structural rot in outside wall cavities. (See Table 2) It is possible to have an average setting on the humidistat, however anytime there is a major change in outdoor temperature it should be adjusted. The marketplace has developed an automatic sensing humidistatthat monitors this and automatically adjusts itself in response to changes in outdoor temperature, making manual adjustments unnecessary.

Table 2 - Condensation on Windows

  Window Types

Indoor Relative Humidity

Single Pane

Double Pane

Triple Pane



-7.7C (18F)

-12.2C (10F)



-11.6C (11F)

-17.7 (0F)



-16.6C (2F)



-2.2C (28F)




-5.5C (22F)




-9.4C (15F)



There may be a problem of too much moisture all the time and in these cases the installation of an Energy Recovery Ventilator (ERV) or Heat Recovery Ventilator (HRV) may be necessary. We will not discuss these appliances in this article, however I do want to explain how one may still require the addition of whole house humidification and have one of these appliances. For the most part ERV's & HRV's remove excessive amounts of moisture from the home.

There is a ventilation code that dictates just how much air needs to be exchanged on a continuous basis to maintain a healthy indoor environment. Some homes and offices are very large with minimal occupancy levels. It is possible and occurs quite often where a homeowner complains that the home is too dry. If the ventilation rate has been checked and is correct, and the controller for the ERV or HRV is in the lowest ventilation rate possible. It may be necessary to add a humidifier to boost moisture levels.

Here again we are striving to achieve a balance. The need for ventilation air while at the same time the need for higher moisture levels. This usually happens in large homes (2000-3000 sq. ft) with two persons occupying the home. More frequently it happens in small office buildings where the building size may be the same as the home, but employs few staff. The difference is that the office environment has no significant amount of moisture being generated other than occupant respiration (breathing). No washing machine, dryer, dishwasher or washing of floors. Definitely not enough moisture being generated, yet the mechanical ventilation system is required to remove pollutants generated from breathing (CO2), photo-coping, printing, perfumes and/or personal body products, carpets and building materials gases to mention just a few.

So, while ERV and HRV ventilation systems may on the surface appear to be in conflict with maintaining optimum moisture levels they are in fact not in conflict because there are so many other reasons to have mechanical ventilation.


Make sure the
  • Saddle valve (water valve) is fully open for winter operation. Don't forget to shut the water off during the summer months.
  • Power cord is plugged in (if applicable) and/or the wiring is secure.
  • By-pass duct damper is open for winter operation. Don't forget to close this damper in the summer.
  • Drain and water reservoir are clean and free of clogs.
  • Water runs freely and that the water float assembly or automatic valve shut off the water flow.
  • Use water conditioner if necessary (depending on your local water conditions).
  • To clean monthly and replace the evaporator media if necessary.

Most homeowners attempt to keep their humidifier maintained but often it is neglected and the evaporator (media pad, wheel or disks) are not cleaned and/or replaced. This reduces the capacity of the humidifier to introduce the moisture into the home.

The evaporator serves two functions, 1) it's surfaces are filled with tiny pores or groves that allow water to be picked up and evaporated from its surfaces, 2) as the water evaporates the heavy particulate is left behind as mineral deposits. Mineral deposits will if left unattended eventually clog these small pores or groves rendering the humidifier nothing more than a reservoir for bacteria, mold, slime. The very things that are in conflict with good, indoor air quality.

We use humidification beginning in late September ending in April, 5 months so, humidifier maintenance is key to a healthy home comfort system. Be certain to clean and replace the evaporator media as recommended by the manufacturer. Remember working closely with your home comfort contractor and technician can help ensure that your family is kept both warm and comfortable all winter long.



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