No matter the type, properly designed, specified, installed, and maintained humidification systems can provide years of trouble-free operation. Taking a proactive approach to humidifier maintenance is the single best way to prevent operational issues and unscheduled humidification system shutdowns. Key factors that contribute to long-term humidifier performance include: product selection, incoming water type, scheduled inspections and maintenance, and software updates.

This article discusses the steps you can take to proactive humidifier maintenance. Following these guidelines will take the headache out of humidification and ensure maximum equipment life.


Selecting a humidification system based on maintenance requirements is the best way to control the cost, frequency, and length of scheduled shutdowns.

When selecting mechanical systems for buildings, things that may seem beneficial at the time of purchase could turn into higher costs down the road. For example, the lowest possible upfront equipment cost might mean more frequent check-ups and high consumable expenses over the life of the equipment. Conversely, a larger upfront investment might deliver payback in the way of maintenance-free operation for months or even years.

Another consideration is the human capital available to perform maintenance tasks. The equipment choice will impact the level of skill and amount of time required for servicing.


Isothermal steam generators with stainless steel tanks operate at peak performance when clean. Over time mineral deposits can build up inside the tank, insulating heaters and heat exchangers. This reduces output and can cause the heater or heat exchanger to fail.

Water hardness and steam output consistency

Water hardness plays a critical part in an isothermal humidifier’s ability to maintain relative humidity set point. If the supply water is harder than 12 grains per gallon, scale buildup will occur quickly. Increasing skim and drain/flush cycles will reduce mineral accumulation, as will regular cleaning.

Drain and flush cycles, which are automated on most systems, completely drain the humidifier for several minutes then flush the system for several minutes more. The key is to remove minerals while they are still in solution and before they attach to humidifier components in the form of hard scale. During this process, the humidifier will be offline for around 15 minutes. There may be additional delay in steam output until the cold replacement water is heated to boiling.

Even with automated drain and flush cycles, build up will form and eventually require the tank to be cleaned. This can be accomplished through use of a manufacturer-recommended de-scaling solution to remove scale from heaters, heat exchangers, and tanks. The tank cleaning process typically takes the humidifier offline for several hours or overnight.

Any time the humidifier is going through a drain/flush cycle or taken offline for maintenance, relative humidity in the space can drop. In applications such as office buildings or other environments humidified to improve comfort, relative humidity fluctuations are not an issue. In process-critical environments, however, a 5 percent fluctuation in the relative humidity can adversely affect processes. Humidifiers in these environments typically use softened, deionized, or reverse-osmosis water, depending on the level of control required. The more critical the relative humidity control, the lower in minerals the fill water should be.

Limiting scale buildup

Preventing buildup in the first place is significantly less time consuming and more effective than dealing with its removal. Mineral accumulation can easily be reduced by using softened or demineralized fill water in the humidifier. Humidifiers using softened supply water will require cleaning, but much less frequently than with hard water, and soft-water scale is very soft and easy to remove.

Using reverse-osmosis or deionized water will eliminate, or nearly eliminate, mineral accumulation altogether. While humidifiers using deionized or reverse-osmosis supply water can run for years without cleaning, quarterly inspections are encouraged to verify proper operation of the water treatment system.

Regardless of water type, proper maintenance intervals should be established to keep mineral accumulation to a minimum. At least annually, it is critical to verify that the humidifier’s fill and drain valves are working properly. At the end of the humidification season, be sure to remove standing water along with any debris to allow the boiling chamber to remain dry during the off-season.

If both tank cleaning and water treatment are beyond the scope of the application, consider an electrode steam humidifier, which has a replaceable steam cylinder. Cylinder replacements can be completed in minutes and do not require any specialized skills or certifications.


The best prevention against humidification system issues is regular inspection and maintenance. All systems should be inspected after the first three months of operation to determine appropriate inspection and maintenance intervals. From there maintenance requirements vary widely depending on the type of humidifier, fill water quality, and frequency of use.

Electric steam humidifiers

Manufacturers of electric humidifiers typically recommend annual (or more frequent) inspection of high- and low-voltage wiring and connection points:

• Look for signs of corroded, overheated, or loose wiring, and verify that all wiring lugs are torqued to the manufacturer’s specifications. Inspections and torque checks will go a long way in preventing excessive heat and degraded wires and components.

• Compare humidifier current draw with the rated current draw listed on the humidifier label. Low current draw can be a sign of heating element failure.

• Replace electrical components that show any signs of degradation.

Parts to have on hand for electric steam humidifiers include: gaskets, heating elements, water level sensors, and humidifier de-scaling solution or replacement cylinders.

Gas-fired steam humidifiers

Manufacturers of gas-fired steam humidifiers typically tune the burners in the factory. Additionally, they recommend checking the products of combustion at least annually:

• Verify proper ignition, and clean the burner if necessary.

• With the manufacturer’s recommended products of combustion guidelines available, and with the humidifier running at 100 percent demand and tank water boiling, measure the following:

o CO levels and CO2 and O2 percentages

o Flue temperature

o Burner efficiency

If any measurements are out of line, see the product documentation or consult the manufacturer for corrective action.

Parts to have on hand for gas-fired steam humidifiers include: gaskets, heating elements, ignitors, water level sensors, and humidifier de-scaling solution.

Pressurized steam injection humidifiers

Manufacturers of pressurized steam injection humidifiers typically recommend annual (or more frequent) inspection of the steam valve and condensate return system.

Steam valve:

• Look for condensate leaks at the valve stem packing.

• Confirm positive valve shut-off.

Condensate return system:

• Confirm that all check valves are operating properly.

• Confirm condensate traps are hot and operational and are not freely blowing steam into the condensate return.

Parts to have on hand for pressurized steam injection humidifiers include: o-rings, gaskets, and strainers. Most manufacturers also recommend having replacement steam traps of the type used by the system readily available.

Adiabatic humidification system considerations

Adiabatic humidifiers, particularly wetted media systems and high-pressure atomizing systems, require very little maintenance.

Wetted media systems can run for several years before media panels need to be changed. If a wetted media system has been operating for more than a year, check the condition of the media. If the media is torn or sagging, replace it, and start the humidification/cooling season with fresh media. This will provide a season of improved performance, rather than trying to get another season out of old media.

Most high-pressure atomizing systems use reverse-osmosis or deionized water; therefore, the need for cleaning is seldom or never. High-pressure atomizing systems typically require inspection and/or maintenance of the high-pressure pump and may need the atomizing nozzles tightened or replaced to correct dripping. Be sure to check the water treatment system according to the manufacturer’s recommendations.

Adiabatic systems that use tap water require cleaning or component replacement to remove deposited minerals. Systems with moving parts (such as rotating disks and atomizers with movable nozzle pins) require periodic parts replacement.

Parts to have on hand for adiabatic humidification systems include: replaceable electronics, water treatment supplies (salt, membranes, and filters), replacement pumps, and sump cleaner.


Regularly updating the humidifier’s controller firmware will ensure the latest operational and troubleshooting enhancements and could prevent you from wasting time on issues that have been solved. Check for signs of board degradation such as a broken traces or burnt components. In many cases, outdated electronics may be easily replaced with modern versions.

Since the controller relies on external devices for information, verify that all safety devices are functioning properly. Your checklist should include the airflow proving switch, duct high humidity limit, low/high tank water cutoff switches, interlock switches, and temperature sensors.


Plan ahead and prevent unscheduled humidification system shutdowns by selecting the proper humidification system for the application, considering water type and its effects on the system, performing scheduled inspections and maintenance, and keeping up on software updates. Careful design, selection, and maintenance will ensure a humidification system that provides years of trouble-free operation.

Publication date: 10/10/2016

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