The importance of indoor humidification for health

Headaches, dry eyes, irritated airways, dry skin and contact lens discomfort are all common symptoms of an indoor environment with low humidity. Because dry air is difficult to detect without measuring it, many people do not realise that their discomfort or reduced wellbeing may be caused by excessively low relative humidity.

The recommended indoor humidity level for homes, offices and commercial buildings is between 40% and 60% relative humidity (RH). Maintaining humidity within this range helps create a healthier and more comfortable indoor environment while reducing many of the problems associated with dry air.

During the Nordic heating season, indoor humidity frequently falls well below the recommended range. Cold outdoor air contains very little moisture, and when it is heated indoors, the relative humidity drops even further. As a result, many offices and other commercial buildings experience humidity levels below 30% RH for extended periods, increasing the risk of discomfort and poor indoor air quality.

One of the first noticeable effects of dry air is electrostatic shocks, which occur below a threshold of 40%RH and can rapidly become a nuisance. Above this level electrostatic shocks are eliminated.

Eyes are particularly susceptible to dry air as the thin layer of moisture on the cornea quickly evaporates. Contact lens wearers express discomfort that can increase by a factor of five as humidity drops from 45%RH to 20%RH, by which stage dust and dirt deposits on lenses increase causing greater irritation. If the air is too dry the skin, scalp and hair also begin to suffer. With no exposure to moisture, skin develops rashes and rough patches, the scalp starts to flake and hair will become brittle.

The nose and throat act as a powerful humidifier for inhaled air and mucous helps protect against infection by trapping microbes and dust. They start to dry up in conditions below 55%RH, quickly resulting in nasal stuffiness, dry mouth and sore throat. Persistently low rH increases susceptibility to infections such as colds and coughs.

People’s perception of warmth varies with rH and it is possible to reduce ambient temperature to provide a sensation of warmth when the humidity is at a comfortable level, so reducing heating costs.

In order to ensure a comfortable, healthy and productive office environment of at least 40%RH, it is essential for most offices to employ some method of humidification. Incorporating a well-designed humidifier within a building’s air-conditioning system will eliminate dry air problems.

All too often the humidifier is the last thing to be considered when planning building services, even to the point of omitting it altogether where cost is an issue and simply leaving a space for a steam humidifier to be fitted at a later date. However, as the cost of retrofitting humidification has been estimated at five times more than incorporating the equipment originally and, combined with the cost of running and maintaining a steam humidifier compared with the alternatives, simply leaving a space for a steam humidifier if building occupants demand it, is not best practice.

There are a variety of factors to consider in selecting the right humidifier for a building such as energy use, water supply, cold water or steam, gas or electric, evaporative or spray, humidifier situation, control compatibility and maintenance needs.

It is therefore important to work with a specialist who is able to provide guidance on the right type of humidifier for your use. It is also important to work with a company that can provide a full range of services, including installation and after-sales service and spares. As humidifiers handle water, they need to be looked after. Particularly important is the capacity for a supplier to offer a fully qualified commissioning service. With respect to the Legionella, for example, the HSE endorses the idea that the best people to commission equipment are the manufacturer or supplier. A planned maintenance schedule should be implemented thereafter to ensure the initial investment is not wasted.