Mike Hudson, director at Manse Masterdor Ltd reveals how tenants can reap the rewards of airtight doors through lower heating bills.

In the past homes were often draughty, and much of the required ventilation was provided by this fortuitous air leakage. However, modern building construction aims to provide an airtight envelope in order for controllable ventilation to increase energy efficiency, eliminate discomfort from cold draughts, and prevent polluted air from entering.

The air-tightness of a building is known as its 'air permeability' or leakage rate. Air leakage can occur through gaps, holes or cracks in the fabric of the building envelope which are not necessarily visible to the naked eye – such as through and around doors, windows and walls. This leads to cold external air moving into the building, and warm internal air moving out of the building. It is generally at its most severe during the colder, windier, winter months and has least impact during the warmer, calmer, summer periods.

This air leakage affects the building's performance and is now firmly enshrined in Part L of The Building Regulations - conservation of fuel and power. Uncontrolled air loss from a building can have a significant impact on occupant comfort, and on what it costs to operate and maintain a building.

Many door manufacturers quote conduction (calculated as U-values) as the key factor for consideration but the most important aspect for reducing wasted energy usage is air-tightness.

Although manufacturers of door sets submit their products for testing to PAS23-1:1999 and the tests do include air permeability (to BS6375), there is no requirement to achieve a certain level. Some manufacturers do not even achieve a recordable air permeability level, but still receive a certificate of testing.

A weather test is performed in which the door is monitored for air and watertightness. The reality is that test results for weather exposure are not always highlighted and a broad range of results between different manufacturers is not advertised so customers and specifiers are left in the dark about how weather tight the door-set actually is.

Few, if any, door manufacturers advertise the results of PAS 23 testing, and results are rarely checked to see how a door has performed and the air permeability is not taken into account. Another area for concern is that door-sets with low test results are being used in numerous locations where a high category door-set is required, including open areas, high ground and high level buildings.

To ensure that specifiers take air permeability seriously, Masterdor undertook an investigation into how wind speed levels affected energy costs through heat loss and Leeds University validated the overall test results.

Initial testing focussed on how heat loss through door-sets can be caused by either conduction or by convection through air leakage. The results revealed that heat loss through conduction is only part of the total heat loss and will not carry the same significance as heat loss through draughts due to poor sealing. Masterdors have two compression seals, one in a concealed rebate that goes all round the face of the door, and a brush pile, all in a double rebated frame.

When assessing and specifying door sets, specifiers often take into account U-values but not necessarily sufficient notice of air permeability which, as the results show, is critical to reducing heat loss and keeping out the extreme weather.

Another part of the Leeds University review considered how heat loss could be converted into monetary terms and how the heat loss cost per day builds up with increasing wind speed. The results showed that wind speeds of just 5mph can result in significant additional cost – roughly 11p per day. Typical wind speeds in Swansea for the month of January is 20mph which would equate to £10.61 heat loss for the month. By specifying an exposure category of 800 Special Masterdor the cost could be reduced to £5.22 or £3.30 using a Masterdor Thermal. (All figures are based on fuel costs at April 2007).

This is not a new message as Manse Masterdor Ltd has been manufacturing airtight door-sets for the past 15 years. Masterdors achieve air permeability levels of 800 Special, an exposure category that British Standards regards as airtight. Savings for the resident can be £60 per door per annum when compared to other door-sets on the market that don’t provide complete air-tightness.

It is important that social housing providers are aware of the discrepancies of product performance and there is no reason why a door-set should leak heat if it has been designed, made and fitted correctly.