Fan power

At last, it seems, humidstat-controlled fans have won the hearts of the British public. Results from a survey carried out by the Building Research Establishment are so positive that AMDEA (the Association of Manufacturers of Domestic Appliances) director general Peter Carver enthused: “We are delighted with the results. These products are endlessly tested in our own and independent laboratories for their performance. But this is the first time we have run independently controlled and assessed experiments in normal houses.”

It hasn’t always been such a sunny picture. As the report reminds us, in its introduction: “Early mechanical types of humidistat control for extract fans were more effective than manual control but gained a poor reputation which, despite improvements in the product with the move to solid state electronic humidstats, the industry has found difficult to shake off.

“Typically, running times were said to be too long, leading to wasted energy and disabling action by occupants who did not like the fan noise.”

However, all that’s changed. And it’s not just the manufacturers who say so. The independent BRE report concudes: “The short, rapid ventilation, closely related to the period of moisture generation, achieved by the humidity controlled fans, is precisely what is required for effective and energy efficient ventilation.”

The project used 15 homes in the South East of England. Humidistat-controlled extract fans were installed in the kitchen and bathroom of each house. Split into three groups, each house went one month without ventilation, one with manual controls and another month with humidstat controls. Householders were interviewed at the end of each month.

Six of the houses chosen were built in the 1930s with cavity walls, pvc-u double-glazed windows with trickle vents and gas-fired central heating from balanced flue boilers; the other nine were constructed in the 1960s with a similar specification but having injected foam cavity wall insulation.

Although the householders, in the initial questionnaire reported a range of problems with moisture, these did not appear to be severe. They had few problems with excessive condensation and no mould. When operating in humidstat mode both fans in six of the houses also had manual control available to the occupants.

The report claims that, “some problems arose due to poor workmanship by the sub-contractor during installation, despite full installation instructions being provided with the products”. Some of the fans didn’t work at the start of the monitoring process owing to installation defects.

Carver adds: “So realistic was the whole operation that we even had one or two installation problems. That’s why the information paper contains a model instruction, advising on siting and warning not to tamper with factory set humidity operating levels without reading guidance very carefully.”

The report referred to additional requirements, specific to humidity-controlled ventilation. It stressed that these products should be installed as high as possible – noting any minimum distance from the ceiling/wall/other objects set out in the manufacturer’s instructions.

It also stipulates: “The humidity level at which this device operates has been factory pre-set – any adjustment should be made only in accordance with the manufacturer’s instructions.”

The survey recorded both the measured and “occupier-percieved” advantages of humidity-controlled extract fans. Most householders said the fans reduced the problem of misting of windows and removing moisture, although none of them had experienced severe problems.

It emerged from the report that householders liked the fans for their ability to clear “steam and smells” from the bathroom and cooking smells from the kitchen, as well as tackling the misting of windows and the removal of moisture.

Generally, the fans didn’t come on as much as occupants thought they would but they were effective in dissipating humidity peaks – which lingered during periods when the fans were disabled during the experiment.

It concluded that fans ran for less time than expected, but analysis of results showed this to be correct operation. Moreover, they were “effective in dissipating humidity peaks more quickly than when they were disabled” and the “short, rapid ventilation closely related to the period of moisture generation, achieved by the humidity-controlled fans, is what is required for effective and energy-efficient ventilation.”

In most cases, fans under humidistat control responded consistently to peaks of water vapour production in kitchens and bathrooms. However, some responded better than others, suggesting that both the location of the humidstat in the room and the sensitivity adjustment are critical to correct operation.

Recorded fan running times under humidstat control, averaging across all the houses, were 1·9 hours per week in the kitchen and 2·5 hours in the bathroom (see Table 1). This contrasts with some 50 hours per week reported for older type humidstats and building stock, as shown from work carried out in the early 1980s.

The factor with the greatest influence over indoor humidity levels observed in this project was outdoor temperature. Lower outdoor temperatures resulted in lower average relative humidity in all rooms in the houses.

Householders were not troubled by the noise from the operating fans – they only ran during daytime and evening.

Backdraught shutters were seen to be desirable in both kitchens and bathrooms, but householders may be disturbed if exposed external gravity-operated shutters rattle in high winds at night.

On a final preference issue, humidstats did not always come on when occupants thought that they should do. Generally, people expected an instantaneous response at the start of a cooking or bathing. This suggests that fitting a fan with both humidistat and manual controls will please the customer.