Heat pumps cause fastener popping! Right?

Article by Kevin Sceats
Winstone Wallboards Ltd.

We’ve seen quite extensive fastener popping issues arise over the last summer but probably no more than usual.
We’ve also heard some stories speculating that the extensive use of heat pumps in new housing is the cause of fastener popping. What we do know is that when heat pumps are used in the cooling cycle in summer, the air can be dehumidified. However you may also have noted that when using a heat pump on the heating cycle in winter, there is a reduction in condensation around windows. The water on cold windows results from the air in contact with the windows cooling down, and the water vapour in the air then condensing on the glass and aluminium frame, because the dew point (>100% relative Humidity) was reached at the glass temperature.

Yes however this isn’t dehumidification. Very simply the warmer the air, the greater its capacity to hold more water vapour . Heating and blowing warm air around the interior of the house will remove water off the windows, but not from dehumidification but rather from raising the temperature of the glass above the dew point of the air. So less condensation on windows in winter is the direct result of having a warmer houses.

Of note is that a heat pump air conditioner will not ventilate a house if all the windows are always shut. There is no air exchange in a typical domestic air-conditioning unit only exchange of heat. The inside and outside of the house are completely isolated unless windows and doors are left open.

So then the question you may well ask is; ‘Does having warmer houses contribute to fastener popping?’ And the answer is most likely! Simply because the timber framing will be ultimately tend to be drier in modern houses due to improved heating and insulation compared to houses built in earlier decades. When fixing plasterboard linings, the best solution is to be more considerate of lower timber framing moisture content before lining (say 12-14% Vs 18-20%). Talk to your builder well in advance to ensure they have a realistic construction programme to allow for adequate drying of framing.

PS: A modern car with fogged up windows on a cold day can use its air-conditioning to dehumidify the air inside the car to speedily defrost the windows. Car air conditioning is ALWAYS in cool mode. But on a cold day, a car counteracts this cooling effect with the vast quantities of heat that the engine cooling system tries to get rid of.

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