Lee B writes:

Me again - mold lady, still deciding what to do about the mold
discovered in the finished basement of the house I'm selling.

I need one that I'm comfortable leaving on unattended in the vacant
house. And it needs a defroster or something, so that when it gets
cooler in the basement it doesn't frost over, or it at least needs to
function at lower temps, which apparently some of them do now.

We use a couple of dehumidifiers in our basement. From my experience,
it seems that the ones with electronic controls are able to deal with
colder conditions while the simpler mechanical humidistat is not.

The one with mechanical controls tries to run whenever the humidity is
high enough. If the air is relatively warm and humid (i.e. summer
conditions), the evaporator coil gets cold but not down to freezing
temperature, water condenses on it, and everything is fine no matter
how long it runs. But when the air is cooler to start with, the
evaporator gets below freezing, the humidity freezes on it, and it
eventually freezes solid and stops doing anything useful. There is
normally a thermostat on the evaporator that's supposed to shut down
the unit while it's iced up, and if that is working properly the ice
will eventually melt and the unit will start working again.

In comparison, the unit with electronic controls somehow knows that it
is collecting ice, and periodically shuts down the compressor and
switches the fan to "high" to melt the ice. So it continues working
in colder conditions.

A timer
would be nice so that it would run a few hr a day, although I suppose I
could buy a timer to plug it into.

No, you don't want a timer, you want a humidistat that runs the unit
whenever needed to keep the humidity below a particular level. When
it's cold and dry outside, that may mean not running at all. When it's
raining outside, the dehumidifier may run most of the time - but you
want it to be doing that to avoid any more mold. Fortunately, every
dehumidifier I've ever seen has a humidistat, though it may not be
calibrated. You may need an external humidity meter to set it.

I'll probably sit it in the shower
stall in the basement (how attractive is that!) and run an extension
cord to it.

That's a solution. Or park it over a floor drain. Some units have a
provision for attaching a drain hose. On our main unit, I've arranged
for its drain to feed into a small-diameter clear plastic hose which
runs under the door into the utility closet where the water heater is,
and it drains into the water heater overflow floor drain.

Or if I could find one that actually pumps water uphill, I
could have it empty into the washing machine's stand pipe, or the sink
in the wetbar.

You can buy special condensate pumps that have a small tank for the
water to collect in, and a small pump operated by a float valve that
empties it whenever the level gets above a certain point. That would
certainly work, but they're relatively expensive ($50-70).

Seriously,
most people I know around here have dehumidifiers in their basements, so
I don't think people would think a whole lot of it. (I just wish I
hadn't let the realtor talk me into unplugging it and hiding it when I
was showing the house, even if it was ugly; I think that musty smell is
what prompted the people to ask for the mold test).

What you *really* should have done is have the dehumidifier there all
the time the house was unoccupied with the heat turned down. That might
have prevented the mold from forming in the first place. Now you've got
mold, and you know about it, so you probably have to disclose it to any
potential buyers. But given that the problem exists, having the house
not smell musty the next time a potential buyer comes through is a good
idea.

(Our house doesn't have any mold that I know of, and it doesn't smell
musty even without dehumidification, but I found that unprotected steel
started rusting in the winter. I have a lot of tools that are at risk,
so we just run dehumidifiers year round to keep the humidity below 50%.)

Dave