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In article ,
says...
Mike Hartigan wrote:
Well, here we are in the midst of another winter of sub-zero
temperatures and I'm having the same problem I have every year at
this time. It didn't go away by itself again this year, so I thought
I'd ask for suggestions.

I built an office addition on my house about 12 years ago. There are
two skylights in this room (the preferred lighting alternative to
windows overlooking the side of the neighbor's house). I also have a
central humidifier which does a superb job (Craftsman 3000, 14 years
old, foam wheel type). As the outside temperature goes down, so goes
the humidistat (that's normal). This seems to keep the condensation
on the skylights to a minimum. Indeed, I use the condensation on the
skylights as a guide to setting the humidistat (simple, yet
effective). In case you haven't already guessed, these skylights are
the most condensation-prone sites in the house.

When the temperature gets into the single-digits or below, I have the
conflicting problems of dripping skylights and static discharges
whenever the kids touch other (which seems to happen a lot more often
under these conditions, but I digress). I dont want to reduce the
humidity further, since the static discharges suggest that it's
already too low. I don't want to increase it, since the condensation
suggests that it's already too high.

I have a ceiling fan in that room, and that seems to reduce the
problem somewhat (it doesn't eliminate it), but I'd like a 'better'
solution. Perhaps something to apply heat to those skylights, or
maybe small fans directed at them? Is this a common problem with a
common solution that maybe I'm just not aware of? I've searched and
can't really find anything that addresses this.

Thanks
-Mike

You are on the right track. I would start by seeing if there is any way
to insulate the skylights themselves. Adding thermo glass and replacing
thing like aluminum frames with a less conductive material like plastic.
would be a good start.

As I said in a response to another post, it's a double pane,
aluminum/wood construction. Technology-wise, it's already designed
to minimize such problems but, physics being what it is, it doesn't
eliminate the problem.

Adding an additional window below that one and allowing some air past
the existing window should also help. The temp difference will be less for
the new window and the air in-between will be less cold that outside and
dryer than inside. Note: cold air hold less moisture than warm. Even if it
is snowing outside with 90% humidity, if you bring that air inside it
becomes very dry as it warms up. The condensation is coming from that 40%
humidity 70º comes in contact with the 10º glass and frame and it cools to
10º and it can no longer hold the same total amount of moisture as it is now
over 100º humidity.

I understand the physice behind the problem (somehow, it sounds so
much more complicated when you try and explain it

Your idea of fans (including the ceiling fan) warms the window a little
and that is why you have less condensation. If you can warm the Frame and
glass enough it would work. Also heat lamps or any heat source would help.

The ceiling fan works fairly well and I've also closed the register
vents in this room, which will reduce the temperature by, maybe 2-3
degrees. More significantly, however, there will be less humidified
air directed into this room. We'll see what happens.

However the real answer are modern skylights designed to handle your
conditions without condensation.

Again, these are 'modern' skylights.

--
-Mike