We have a family run aquatic shop. Due to the high humidity from the fish tanks the front glass of the shop streams with water at night when all doors are closed.

There is a small ventilation vent along the top of the windows but make no effect.

We could install a warm air curtain at the base of the glass which I am sure would solve the problem but the installation and running cost would be considerable. Alternatively we could add mechanical vent but again the costs would be high.

We had thought to install secondary double glazing (there is only single glass there at the moment) with possibly trace heating at the bottom of the glass between the single and double glazed units when it is really cold but are not sure if this would work adequately.

The tanks are maintained around 22 deg. C and there is no other heating ( we did put a low wattage tube heater at the bottom of the glass which had a minor effect but needed to be much higher wattage and thus expensive).

During the day the door is left open so there is little problem. I have not taken a night time wet/dry bulb temperature reading but have assuned it would be around 18 deg. C at high humidity.

  • Pheiffer Property Services

    As you have suggested A belt and braces method in your case would be to replace the sheet glass with A rated double glazing(ensure that you are issued the appropriate certification documents to validate the spec and performance of the glass) then I would recommend the installation of a secondary internally double glazed screen or perhaps a mobile screen which can be removed during trading hours made from marine ply varnished and backed by a 50mm rigid insulation such as cellotex all depending on your circumstances and budget etc… the secondary screen should be spaced so as to allow a low energy passive heat source and finally the perimeter of the area between the 2 screens should be well sealed, in the case of a temporary screen it is to be tight fitting into the aperture to avoid cold bridging. thus your heater needs only warm a small area of air locally to the window enough to push the dew point out to the external face of the glass.
    The less the distance between the two screens the less the heater has to work to achieve the desired result.
    You may even find the setup works without secondary heating.
    It is a question of trial and error starting with the internal screen and monitoring the results, then move onto replacing external glazing and monitor as before with heating being the last resort.

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