On Sat, 31 Jan 2004 15:35:27 -0500, "Ray"
wrote:

Doug,

There are many things to consider when working on boosting humidity. Unless
the room is sealed off from the rest of the house, anything you do will be
attempting to humidify the whole house.

It's a regular room that's totally enclosed except for an interior door that
gives access to the rest of the house. I haven't sealed the door.

I did install a fan to vent excess humidity to the outside via clothes dryer
ducting to a roof vent. The fan is controlled by a humidistat. When I water the
humidity soars to 87-90% during the night and down to perhaps 75% during the day
as the room heats to about 79°F. Night temp is about 64-68°F. Wish now I'd
installed a quieter fan (it's next to my bedroom) with 110CFM instead of the
noisy 50CFM one. Thought it'd draw too much humidity out. No way. It'd go all
night if I let it after I water. And that's just to get it down to 80%. So
that's a project I'm going to undertake this fall. The space under the door is
where the fan draws air as it expels the room air. As the room dries off from
the watering the humidity drops to perhaps 50% before the next watering. This is
without an humidifier (or equivalent). I've found that adding an humidifier did
even things out and prevented that sort of drop.

As this isn't a greenhouse situation I do have to be aware of the effect of
excess humidity on the gyprock (plasterboard?) walls. Already had to redo a part
of the single windowsill because I wasn't bailing it enough when I first set
this up. Now that's a daily chore. And there's no water source in there to hook
a fogger to. I did have a look at the smallest JBird. Seems way in excess of
what I need in winter though in summer I do keep the window open to cool the
room down so it'd probably be suitable then. 2 gallons an hour seems too much.
Think .5 might be more suitable. Is there such a thing?

Doug

If we assume that the room IS sealed off, and has an 8' ceiling, the volume
of the room is 480 cubic feet. At 80°F, 100% RH occurs when there is about
250 ml of water in the air. If we assume your whole house is about 1600
square feet of floorspace, that's a volume of 12,800 cubic feet, meaning
that the 100% RH level needs almost 6.6 liters of water! If we drop that
back to 65% RH, it still means that there must be 4.3 liters of water in the
air.

Knowing full well that your house is not likely to be totally sealed, you've
got to figure on moisture escaping to the outside, meaning that you have to
keep adding it. (I sure wish there was a way to know what that rate was...)

Anyway, you're better off with something with a large capacity, and
connecting it to a humidistat, rather than getting something small and
hoping it is enough.

As an example, in a friend's greenhouse - about 2000 cubic feet and tight
except for around the door - there is a 2 gph fogger, and in the really
cold, dry days lately, it works full time to maintain 70% humidity. At
70°F, that volume only holds 0.2 gallons of water, so he's losing 10x that
in an hour!

By the way, I put a moisture-capacity calculator on my website if you want
to play around:
http://www.firstrays.com/moistcalc.htm