HUMIDIFICATION & DEHUMIDIFICATION
Best practice for steam humidifiers
Jordan Stevens, sales manager at Condair, outlines the key considerations for HVAC contractors when specifying and installing electric steam humidifiers for air handling units
F
or many HVAC contractors, the most familiar humidification technology will be the self- generating electric steam humidifier. These
systems are widely used for humidifying air handling units, although fan unit options are also available for direct room applications. In most commercial projects, however, AHU humidification remains the standard approach. Electric steam humidifiers are typically available with either resistive or electrode boiler technology. Resistive models generate steam using a heating element, while electrode systems pass an electrical current through the water itself. Although maintenance requirements vary between the two, their installation principles are broadly the same. A typical system consists of the humidifier
unit, usually wall-mounted, connected by a steam pipe to the air handling unit, where a steam lance introduces moisture into the airstream. Depending on the application, the installation may also include humidistats, sensors, water treatment equipment, and in some cases pumps or tanks. One of the first installation priorities is to position the humidifier as close to the AHU as possible. Keeping the steam line short helps preserve efficiency by minimising heat loss and condensation within the pipework. Excessive pipe runs, particularly those with multiple bends, increase the likelihood of steam condensing before it reaches
Left: Jordan Stevens, sales manager at Condair
A minimum clearance of 85mm from the floor and 165mm from the ceiling should be maintained to reduce turbulence and prevent condensation. In practical terms, this means a steam lance should only be used in ducts with a minimum height of 250mm. Adequate straight ductwork is also needed
the duct, wasting energy and reducing available humidification capacity. As a rule, the steam pipe should not exceed 4m in length, with each bend effectively reducing the allowable run by 1m. The humidifier will require electrical, water supply
and drain connections. Care should be taken not to position the unit directly above the drain point. As drain water can be discharged at temperatures of up to 100°C, rising vapour may condense on or inside the cabinet, creating a risk of corrosion over time. The positioning of the steam lance within the duct is equally important. The aim is to ensure that steam is absorbed evenly into the airflow without causing wetting on the duct walls or downstream components. In most cases, a single lance should be installed around one-third of the duct height from the floor and extend at least 75% across the duct width. This arrangement helps deliver steam into the airstream effectively while avoiding contact with the duct surfaces.
upstream of the steam lance. At least 300mm of clear distance should be allowed ahead of the injection point, free from bends, transitions or branches, so that airflow remains stable and does not deflect steam onto the duct surfaces. Downstream clearance depends on the steam absorption distance, which must be protected from obstructions to avoid condensation. No bends, transitions or other components should be located within this zone. Absorption distance is determined by factors such as air temperature, humidity, velocity, and the number and type of steam lances installed. For example, in an airstream of 2.5m/s at 20°C and 50%RH, standard steam lances will typically require an absorption distance of around 1m. This can be reduced significantly, by as much as 70%, through the use of short evaporation manifold systems. Manufacturers should be able to confirm the exact absorption distance for the operating conditions of a specific project. Where submicron filters are installed downstream of the humidifier, a clearance of at least 2.5 times the absorption distance is recommended to prevent moisture carryover being captured by the filter. For sensors or high-limit humidistats installed in the duct, the recommended distance increases to five times the absorption distance, allowing the air and moisture to mix fully before measurement. In many cases, the preferred location for sensors is in the return air duct, where they can provide a more accurate indication of room conditions. Installers should also consider fitting a drip tray beneath the steam lance to help protect the duct from corrosion. Just as importantly, humidifiers require routine servicing, so safe and practical maintenance access to the unit must be allowed for at the design stage. Finally, commissioning should ideally be carried
out by the humidifier manufacturer or an approved specialist. This helps verify that the system has been installed correctly, the controls are properly configured, and the unit is operating at optimum performance from day one.
14 July 2026
www.heatingandventilating.net
DOWNLOAD THE HVR APP NOW
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32
