Using Humidistat in crawl space

Mon Jan 30, 2012 1:22 am   

I have a Honeywell H600A humidistat (http://www.longviewweb.com/h600a.pdf)
that I'd like to use in the crawl space of my house. I know that this
controller is intended for indoor use, but I want to use it to control a
couple of powered foundation vents.
Is there any reason why it would be harmed or come to an early demise if I
mounted it in the crawl space (away from any possibility of rain contact, of
course)?

--
Dave M
A woman has the last word in any argument. Anything a man says after that is
the beginning of a new argument.

Mon Jan 30, 2012 1:59 am   

On 1/29/2012 4:22 PM, Dave M wrote:

You will get contamination from critters.
I'm always amazed at how creative spiders can be at messing up stuff.
Can help that with insecticide in the vicinity...unless that messes
up the sensor.

I'm sure people can come up with exceptions, but as a general rule,
If you have a wet crawl space, measuring humidity is redundant.
Run the fan all the time, and
work on making it a dry crawl space.

If you have a dry crawl space, measuring humidity is unnecessary,
and you don't need a humidity controlled fan.

I always get confused when talking about humidity. I never quite know
what people think they're saying and if they're using terms that
accurately describe it.

Most everything is described in terms of relative humidity, cause that's
what
the gauge you bought at walmart shows.

Most of what I try to "fix" is related to dew point. But that's not what
my walmart gauge measures.

Example:
Right now, it's
46F 94%RH outside
54F 60% in the crawl space
47F 86% in the attic..the attic lags the outside humidity.

I'm using cheapo remote sensors of questionable accuracy,
but
if you look up the numbers on the Psychrometric chart, the dew point,
or the actual amount of water in the air is about the same.

Blowing air from outside into the crawl space wouldn't change the amount
of water in the air at all...or the RH reading...for constant
temperature. It would just increase the heat flow thru the floor to
warm that
outside air.

I bought a humidity controlled crawl space vent at a garage sale.
I decided that the cost of getting power to it, while still meeting
NEC, was prohibitive. And it wouldn't make any difference anyway.

Bottom line, make sure your fixing the problem you think you have.
mike

Mon Jan 30, 2012 6:08 am   

On Jan 30, 12:22 am, "Dave M" <dgminala4...@mediacombb.net> wrote:

do you need a controlled fan instead of passive ventilation?


NT

Mon Jan 30, 2012 7:42 pm   

On Jan 29, 7:22 pm, "Dave M" <dgminala4...@mediacombb.net> wrote:

It is completely unsuitable for crawl space humidity control- wrong
component, wrong algorithm.

Mon Jan 30, 2012 9:05 pm   

On 1/30/2012 9:42 AM, Fred Bloggs wrote:

More words please.
What's the algorithm and how does it differ from one designed for use in
the crawl space?

Mon Jan 30, 2012 9:52 pm   

NT wrote:

Yes, I do need powered vents. I have seen mildew spots on large areas of
the underflooring. There's no standing water that I can see, but the ground
is wet. It has stayed wet almost constantly since early October (winter is
out wettest season).

--
Dave M
A woman has the last word in any argument. Anything a man says after that is
the beginning of a new argument.

Mon Jan 30, 2012 10:10 pm   

"Dave M" <dgminala4444_at_mediacombb.net> wrote in message
news:naKdnf_Waolln7rSnZ2dnUVZ_qKdnZ2d_at_giganews.com...

and my crawlspace has 6 or 8 mil black plastic sheeting covering the ground
and it is sealed to the foundation walls. I have passive ventilation and no mild,
mildew, whatever anywhere.
Art

Mon Jan 30, 2012 10:17 pm   

"Artemus" <bogus_at_invalid.org> wrote in message news:jg710b$6ur$1_at_dont-email.me...

Art

Tue Jan 31, 2012 7:26 am   

Dave M wrote:

(...)


You probably don't.

I suspect you need a 'French Drain' which is a peripheral
trench around your home that provides an easy way for
water to exit into the storm drain before it enters your
crawlspace.

http://en.wikipedia.org/wiki/French_drain


--Winston

Tue Jan 31, 2012 11:04 am   

On 2012-01-30, Dave M <dgminala4444_at_mediacombb.net> wrote:

unless It's succeptible to extreme temperatures that could be present
there but not found indoors I can see no problems.

--
⚂⚃ 100% natural

Tue Jan 31, 2012 11:13 am   

On 1/30/2012 12:52 PM, Dave M wrote:

If it were me, the first thing I'd try to do is kill the mildew. And if
it's
in a place that could migrate up a wall, I'd worry a lot about that
from the
standpoint of health and long term destruction of the structure.
Somebody else can recommend whether you need to seek professional help.

Then I'd do some math. How much volume in the crawl space.
How many CFM for the vent fan?
Assuming perfect air distribution, how long does it take to change the
existing air for outside high-humidity air?

If the crawl space is much warmer than outside air, the RH will be somewhat
lower than the outside air...consult the psychrometric chart.
But that means you don't have a big enough fan.
That also means you've got a lot of heat lost thru the floor.

Then, I'd wire up the fan temporarily.
Measure the humidity.
Run the fan continuously until the humidity reaches your target value.
Turn the fan off.
Monitor the humidity as it rises.
Plot the graphs.
Possibility 1...the humidity doesn't decrease significantly.
If the ground is wet, you can expect the humidity to be at the
saturation point. A small fan is inconsequential.
Possibility 2...the humidity rises so fast that you might
as well leave the fan on all the time anyway.
Possibility 3...????? I can't think of one.

Unless you have a fan capable of drying the ground, I don't have
high expectations.

You need ground cover.
Depending on how wet "wet" is, you may need to find out how
the wet is getting in there and fix that.

I think the early demise of the humidistat is the least of your worries.

Tue Jan 31, 2012 4:32 pm   

Winston wrote:

Perhaps a French drain would work. but installing powered vents would be
much less expensive and much easier to install. I already have the
humidistat, and the powered vents are relatively cheap and easy to install.
The majority of the work to be done will be to run power to the crawl space.
That will be fairly straightforward as well.
Thanks for all the comments.
--
Dave M
A woman has the last word in any argument. Anything a man says after
that is the beginning of a new argument.

Tue Jan 31, 2012 4:46 pm   

Dave M wrote:

We had a serious 'standing water' problem in our crawlspace
after every rain. After installation of the French Drain
and clearing a few obstructed foundation vents, the crawlspace
remains quite dry during all but the very worst downpours.

(Even during power failures.) :)

--Winston

Tue Jan 31, 2012 6:19 pm   

On Jan 31, 10:46 am, Winston <Wins...@Bigbrother.net> wrote:

French drain should be required by the local building code. If he
already has one, then it's clogged. Another requirement is that the
grade slope away from the foundation slope at least 6" for 10'.
Although not a requirement, another recommendation is that the rain
gutters be channeled a minimum of 10' from foundation, this is done by
attaching the same 4" poly tubing either on or under the ground for
that distance, with minimum 1/4" per foot of run slope for standard 4"
pipe. Many times there is a watershed issue where the foundation is
located on the down hill side of surrounding area. This is handled by
excavating a swale to divert the water from around the vicinity of the
house. A swale is a simple three sided trench filled with no.3 stone
to prevent erosion. Lastly, regardless of the drainage, a 6-mil vapor
barrier is used to cover the ground inside the crawl space, plastic is
staked in place, seams overlapped by minimum 6" and taped or glued,
also it is run up the interior walls by 12" and taped/glued. Crawl
space ventilation does not work and is no longer recommended.

Tue Jan 31, 2012 7:01 pm   

On Jan 30, 3:52 pm, "Dave M" <dgminala4...@mediacombb.net> wrote:

That's a serious problem and could end up killing you and the other
inhabitants eventually, nearly all mold is toxic to one degree or
another. Do you have insulation in the floor joists, and if so does it
have a vapor barrier? One seemingly paradoxical problem with most
vapor barrier technology is that it is vapor permeable but watertight,
and is designed to be used only for vertical installation and not
horizontal, TYVEC is a pefect example. This means that the usual high
interior humidity during the winter season permeates the flooring,
condenses to liquid on the vapor barrier and is trapped there. If you
want to install instrumentation then consider a wood moisture
indicator. Mold growth begins when all of the following are exceeded:
RH in excess 70%, temperature exceeds 70oF, wood moisture content
exceeds 17%.