Spending as little as 10 minutes discussing proper humidifier operation and troubleshooting tips with the homeowner at the time of installation or service could eliminate future callbacks.

Here are some simple strategies that can be used to ensure proper operation and keep homeowners happily humidified while avoiding costly callbacks.

Achieving Optimum Humidity

1. A humidistat, used with a manually controlled humidifier, needs time to react to an increase or decrease in the call for humidity. Make sure your customers clearly understand the reaction time difference between a thermostat and a humidistat.

A call for a change in humidity takes much longer to fulfill than a call for a change in temperature. Therefore, it's best to make a humidistat adjustment in the morning for what the anticipated evening low temperature will be. For instance, if the low temperature is expected to be 20F, the relative humidity should be set for 35%. The humidifier should be adjusted for every major change in outdoor temperature (see Table 1 for recommended settings).

To avoid making constant manual adjustments, the homeowner can opt for a new automatic humidifier control, which constantly monitors indoor humidity and outdoor temperature to respond immediately to a humidity call.

2. Run the furnace blower constantly. Whole-house humidifiers work in conjunction with the furnace blower motor. If the blower operates constantly, every time a humidity call is made, the call will be fulfilled immediately. In addition, if there's excess humidity in the home, the furnace blower will effectively dissipate excess moisture over time.

For new, tight homes, an energy recovery ventilator (ERV) can also be used to remove excess moisture from the home. With ERVs, inside air can be circulated more effectively and efficiently.

3. Explain the basics of humidification. Common sense might lead the average customer to assume that as temperature decreases, the humidifier adjustment would need to increase. However, the exact opposite holds true. As air becomes cooler, its capacity to hold moisture decreases. Therefore, when the temperature dips to below freezing, the recommended relative humidity will decrease and the homeowner will need to set the humidistat dial lower.

Although no one will ask you to predict the weather, it would be worthwhile to don your weatherman's hat and quickly explain relative humidity to the customer. The term is unfamiliar to many people, but it plays a critical role in comfortably humidifying a home.

Simply put, relative humidity is the amount of water vapor, in percent, that's actually in the air, compared to the maximum amount the air could hold at the same temperature.

For instance, air in a home heated to 70F can hold approximately eight grains of moisture per cubic foot, which would be 100% relative humidity (RH).

If there are currently two grains of moisture per cu.ft. in the home, then the air is holding one-fourth, or 25%, of its total capacity. The relative humidity is then 25% because it could hold four times as much moisture. Of course, the goal is never to reach 100% relative humidity. Optimum humidity varies depending on whom you ask, but most agree a comfortable range is between 40% to 60%.

4. Change the evaporative element annually. Most homeowners don't realize how critical the evaporator is to humidification. It's the heart of the unit and must be in good condition to ensure high capacity and trouble-free performance.

Its importance can be illustrated in two ways:

1) First, it's the means by which moisture is added to the air. Its many tiny surfaces allow water to be dispersed and then evaporated for distribution as moisture.

2) Second, it traps minerals left behind from the water passing through it. As the mineral deposits build, the humidifier's evaporation rate could be affected.

How to Avoid Over-humidification
What if the homeowner follow all of the tips for achieving optimum humidity, yet experiences condensation on windows instead? Often times, the fault lies beyond the humidifier and its control and can be attributed to other household conditions.

For instance, just by talking and perspiring, people add humidity to a home's air. During the holidays, at a household event with numerous guests, condensation may sometimes appear on cold, outside windows.

To keep windows from fogging, decrease the humidistat before family gatherings. Inform the homeowner that moisture from internal sources other than the humidifier will not immediately dissipate once the temperature drops and condensation appears.

Other humidity-causing household events include cooking, boiling water, taking showers, and watering plants.

While none of these events can bring enough moisture into the home for comfortable, cold weather living, any one, given the proper circumstances, can elevate the humidity level high enough to cause condensation on windows.

Furthermore, this excess moisture can occur even when the humidifier is off or in homes without a humidifier. Therefore, remind the homeowner that, on occasion, this is normal.

With a constant indoor temperature of 70F, Table 2 illustrates the outside temperature at which condensation is likely to occur.

Homeowner's Humidifier Checklist
After completing the service on your customer's humidifier, here are few tips to leave behind with customers to ensure their unit's continued peak performance:

  • Make sure saddle valve is fully open.
  • Make sure power cord is plugged in, if applicable.
  • Make sure bypass damper is open during winter, closed in summer.
  • Make sure drain is free of clogs.
  • Make sure water runs freely and water line is open.
  • Change evaporative element annually.

Finally, if optimum humidity and minimal maintenance is the goal of the end-user, you may want to suggest installing an automatic humidifier.

With an automatic humidifier, routine maintenance, such as changing the evaporative element will still be required, however the need to make constant manual adjustments to the humidistat will be eliminated.

Nevertheless, regardless of what type of unit your customer has, regular service will ensure optimum performance and comfort for years to come.

Table 1. Recommended Indoor Humidity Levels
Outside Temperature Recommended Relative Humidity
+40F 45%
+30F 40%
+20F 35%
+10F 30%
0F 25%
-10F 20%
-20F 15%

Table 2. Common Occurance of Condensation on Windows
Indoor Relative Humidity Window Type
Single Pane Double Pane Triple Pane
50% 43F 18F 10F
45% 38F 11F 0F
40% 34F 2F -10F
35% 28F -8F -25F
30% 22F -20F -35F
25% 15F -30F
20% 8F
15% 0F
10% -11F

Bruce Darkow is product manager for Aprilaire's humidifier line. He can be reached at bad@aprilaire.com.

Give us your feedback on this article at letters@contractingbusiness.com