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On the street, temperatures at night are about -5 °С and about 8 °C during the day. In the apartment it is about 25 °C. So, there is condensation on the windows and I don't want to wipe the windows every time.

How do I prevent condensation on the balcony windows?

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air the room out once in a while to get rid of the humidity – ratchet freak Sep 23 '13 at 7:58
up vote 9 down vote accepted

You're dealing with a basic fact of nature, water condenses on cold objects, so you need to either remove the water or the cold objects. The windows will typically be the coldest objects in your home since they have such a low R value.

Start by reducing the humidity in your home, run exhaust fans in the kitchen and bathroom for longer when cooking and showering to remove the moist air. You can also install a dehumidifier to dry out the air.

The second step is to make the windows warmer by upgrading them to double paned insulated windows. If your windows are old, this can also save you money with lower heating and cooling bills.

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Unfortunately, dehumidifying the interior air won't be enough during cold nights. A -5 to +25 °C gradient means that to prevent condensation, the interior relative humidity will have to be below 10%—which is unhealthily dry. From +8 to 25 °C is much better: Condensation will occur only at R.H. above 32%—dry, but somewhat comfortable.

Reducing the interior temperature to 20°C is recommended for energy conservation purposes, but this step alone also will significantly reduce the condensation. Must you have it so warm indoors? At 20°C, the R.H. thresholds are at 20% (cold night) and 45% (day).

There are winterizing kits consisting of clear plastic sheeting which can be attached to the window surround (either inside or outside) to form an air barrier between the plastic and the glass. They come in various clarity steps. The more diffusive might be an advantage if you like light but not eyes peering in. They are easy to install today and remove in the spring.

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We used to get a lot of condensation on our windows until we installed a ventilation system. Our indoor temp in winter with our fire going is around 22-23C. We wake up to temps at the lowest of around 11-13C. The dryest I've seen it get is 42% RH. Condensation is very minimal. – Matt Sep 23 '13 at 23:23

We put one of these in our home and no longer having pools of water all over the window sills. On extremely cold days there can be a little condensation, but it's significantly less

It's not a true heat recovery ventilator, but it does recover heat from the ceiling space.

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