The Effectiveness of Draught Sealing & Secondary Glazing
How much heat do you lose through draughts in your home?
Up to 25% of heat loss in a house can be due to draughts leaking through windows, doors and chimneys1.
A 5 mm gap under a door can let through up to 80,000 litres of cold air per hour2. That is enough cold air to three quarter fill an Olympic sized swimming pool every 24 hours!
How much do draughts contribute to heat loss from traditional wooden sash windows?
Up to 60% of the total heat loss from a window can be due to draughts2.
By how much can draughts from wooden sash windows be reduced when using the Sealasash perimeter sealing system?
Independent tests show that by draught sealing, air leakage can be reduced significantly by up to 86%3.
How effective is secondary glazing?
A draught sealed traditional wooden sash window has a typical thermal transmittance/heat loss coefficient (known as the U value) of between 4.2 and 4.5 W/m2K 3,4. The lower the U value the more thermally efficient the windows are.
Up to 72% of conductive heat loss (heat loss through solid materials) in a single glazed wooden window comes from the glass, while heat loss through the wooden frame is much less3.
Draught proofing + Secondary glazing = 63% reduction in heat loss with a U-value W/m2K of 1.743.
How can an even better U value be achieved without altering my windows?
Combinations can make wooden sash windows even more efficient, thereby offering more comfort and lower heating costs.
Draught proofing + Secondary glazing + heavy curtains = a 66% reduction in heat loss with a U-value W/m2K of 1.333.
Draught proofing + Secondary glazing + shutters provides = a 75% reduction in heat loss with a U-value W/m2K of 1.133.
How do I achieve the best result for my windows?
Each circumstance will vary depending on the style of your house and windows (e.g. many houses do not have shutters). However, by repairing joinery and combining draught proofing with secondary glazing, the total heat loss could be significantly reduced.
English Heritage state:
“By combining repair with draught proofed secondary glazing, total heat loss could be reduced to one-quarter of that of the window in its original state; and by even more at night with shutters, curtains or blinds in place. Thus it is certainly not essential to replace existing windows to obtain levels of improvement in thermal performance that make traditional timber sash windows comparable with standard modern windows.”
How much can I potentially save on my heating bill?
Up to 25% of your heating/cooling bill can be saved by reducing draughts5.
Individual savings will vary depending on circumstances but it makes sense to seal out draughts to have more control over your heating/cooling.
(1). Sustainable Living Tasmania, Windows Information Sheet (June 2009)
(2). Draught Proofing Advisory Association, www.dpaa-association.org.uk/householders.htm
(3). Historic Scotland, Thermal Performance of Traditional Windows, prepared by Dr. Paul Baker (Centre for Research on Indoor Climate & Health, Glasgow Caledonian University) October 2008, Technical Paper 1
(4). English Heritage, Research into the thermal performance of traditional windows: timber sash windows, Chris Wood, Bill Bordass, and Paul Baker, October 2009
(5). LivingGreener.com.au; www.livinggreener.gov.au/energy/heating-cooling/draught-proof-home – Draught-proof your home
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