Dew Heating when the Roof is Closed

My scope is in a fairly large observatory with about 8 other scopes.
There's a dew strap around the scope, a dew heater in the camera, and a heater in the flip-flat cover.

When the roof is closed due to cloudy weather, is there a best practice for when to turn on the dew heaters?
For example, tonight the humidity is high, arouond 95%. But that's outside, my Pegasus is reporting the humidity inside the observatory is 56%.

So, assuming the roof won't open tonight as it's supposed to be very cloudy throughout the night and into the morning,
What's the best approach?

Thanks!
Jerry
https://www.youtube.com/@astromusicvideo

I wouldn't worry about it Jerry. With the roof closed your equipment isn't going to drop below the dew point temperature. Think of your car in an unheated garage…have you ever seen dew on it?

The highest dew-point ever recorded was 35 degC. Just saying…

Nonetheless I would recommend leaving the dew heater on continuously as rasing the temperature reduces the humidity and in doing so, reduces the risk of fungus.

I'd also suggest a couple of times a year open up the observatory on a sunny day and give the insides a good dose of sunlight (including UV) inside, including the optics, the inside of the OTA, camera, eyepieces and the rest - though being careful not to let the objective form an image of the sun somewhere which will do damage or worse, start a fire.

We have had several very wet years here and a good friend of mine has an observatory - with a permanently mounted premium 150mm triplet refractor (cost over $15k). Last month he was heartbroken to find it is now growing fungus inside the objective and has been advised there is no professional help; either DIY or replace. And it implies the whole observatory is probably loaded with fungal spores.

I typically have NINA set up so that it looks at the humidity at the scope (sequencer powerups) and runs the heaters as required and will not shut down the sequence (and therefore the heaters) until the humidity during the day has dropped below 80%.

Thanks everyone for responding..

Jerry

I leave my dew heaters on 100% of the time.

When the roof is closed, your equipment is not exposed to the sky. So, unless fog is forming inside the building, you will not get condensation on your scope. There is generally no need to run your heaters when the roof is closed.

John

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