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At the start of the year (2021), it was suggested to me on another forum that heating tape might stave off formation of condensation on the bottom metal sill of a poorly insulated window. It is a rental unit in a highrise, and the windows will not be replaced any time soon.

It was suggested that heating tape might be found in pet stores for terrariums that house reptiles. None of the stores in my city have them. Googling revealed that there are pipe heating heat tape and heating cables.

I prefer the heating cables, despite their greater expense, since they are self-regulating. I was thinking of taping them down to the bottom sill with heavy duty outdoor tape.

Does this sound like a reasonable solution?

P.S. Over the years, I've had to use a dehumidifier on maximum, but it really takes a toll on the lungs. On cold days, even running it continuously is not sufficient.

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Yes, you need to get the temperature of the window frames above the dew point. In my condo that's around 15C.

I have been doing this for the last year: roof/gutter de-iceing cable on the window frames with electrical tape, and a ZooMed ReptiTemp RT600 thermostat to control the temperature of the window frame.

Reptile heater cables are typically about 3 watts per foot. Roof/gutter de-icer cables are typically 5 watts per foot. I tried both, and found the extra power of the roof cables is better. For me it works down to about -10C outside. Below that I'll still get condensation. I did see a 7 watt per foot cable somewhere, but I don't remember where.

My window frames are un-insulated aluminum from about 1980, in a highrise condominium.

There is a product from Austria designed to do this called T-stripe: https://www.t-stripe.com/en/. When I looked into it, the cost of importing the product was significantly more than buying a roof heater cable and the reptile thermostat control. Maybe that has changed now.

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  • I upvoted your answer but can't mark it as the answer unless I try it. In past years, I used cables for gutters, but they only kick in when it gets deeply sub-zero (celsius), so it rarely activates. I tape them to aluminum window frames indoors. I used to use a current meter adapter to see when it's working. I don't even bother these days. The very low threshold temperature is one factor, but we are also getting warmer winters, so it doesn't get as cold. Jan 18 at 17:22
  • As a simultaneous measure, It helps to keep the dehumidifier running continuously. It used to dry out my throat badly, but just keeping the air currents away from the face mitigates that problem a lot. Jan 18 at 17:23
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Any heating method will work - all you need is to get the surface above the dew point.

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  • Thanks, Solar Mike. Do you know of anyone who has tried this before? Any possible wrinkles to watch out for? Aug 17, 2021 at 6:12
  • Check out heated bathroom mirrors… I use a dehumidifier in my bathroom and am looking at a ventilator with heat exchanger.
    – Solar Mike
    Aug 17, 2021 at 7:38
  • From what I could Google, it is a heating pad behind a mirror. My windows are huge, so that would not be practical. The mould usually forms on the sill, so I'm seeking ways to heat the sill. Aug 17, 2021 at 16:36
  • @user2153235 so you know what the dew point is now, at least.
    – Solar Mike
    Aug 17, 2021 at 17:05
  • I looked it up in years past, and looked it up again now. It's the temperature at which the partial pressure of water in the air equals the equilibrium partial pressure for air above liquid water. This condition corresponds to a relative humidity of 100%. It depends on how much moisture there is in the air. Aug 17, 2021 at 19:49

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