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Home Repair - - If it ain't broken, don't fix it. Otherwise look here.
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Posted by m Ransley on July 11, 2005, 7:36 pm
What nick is saying nobody will ever know as he advocates flooding your
basement floor in winter for humidity and shrink wrapping your house to
stop air exchanges. I use a basement dehumidifier it only ads a few
degrees of heat which I welcome as my basement is always cool. My
dehumidifier costs 3-4$ a month to run, a furnce fan running 24x7 would
cost me 35 $ a month.
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Posted by on July 12, 2005, 9:04 am
>What nick is saying nobody will ever know as he advocates flooding your
>basement floor in winter for humidity and shrink wrapping your house to
>stop air exchanges...
I'm afraid you have erred, my good man.
Nick
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Posted by on July 12, 2005, 8:50 am
>nicksanspam@ece.villanova.edu writes:
>>>...I can keep the Basement's humdiity level below 60% as long as I leave
>>>the blower motor on the Furnace/AC system turned on all the time. This
>>>causes some of the basement air to circulate throughout the rest of the
>>>house (with the rest of the house still having humidity below 50%). Would
>>>I be better off with a dehumidifier rather than leaving the blower motor
>>>on all summer?
>>
>>A dehumidifier would add significant heat to the house in summertime...
>...am I right in interpreting that you are basically saying that
>a dehumidifier is going to be relatively helpless against a cold slab
>with warm, humid outside air?
It would work, if the air leakage is not too large. For instance, if C cfm
of outdoor air with wo = 0.0134 pounds of water per pound of dry air leaks
into a 55F 60% RH wb = 0.0051 Baltimore basement on an average July day,
a 40 pint per day dehum could keep up as long as 24hx60C0.075(wo-wb) < 40,
ie C < 45 cfm, or more, if the dehumidifier and the incoming air warm the
basement, BUT that uses lots of electricity and makes lots of heat, about
1.6x40x1000 = 64K Btu/day. You might run a 5K Btu/h window AC 13 hours per
day to remove all that heat :-)
It can be a lot more energy-efficient to use a fan to circulate air between
the basement and the house when the basement is humid, warming the basement
and cooling the house.
>(Plus we have the added comlication of dampness (not puddles) seeping
>in during rainstorms?
Maybe we can adjust the gutters and downspouts and
slope the soil away from the house to improve that.
>So if a large cold slab stores so much moisture...
The long term moisture content of concrete might be 5% of the RH
of the air surrounding it. Concrete weighs about 150 lb/ft^3.
>...what is the best thing to do?
> - Heat the slab?
Maybe a little, in wintertime, by moving air from the basement floor up
into the house. A Baltimore basement with 10 cfm of outdoor air leakage
might be 53 F in January, with Pa = 29.921/(0.62198/0.0025+1) = 0.120 "Hg
vs Ps = e^(17.863-9621/(460+53) = 0.440 "Hg at 100%, and 100Pa/Ps = 29%.
Circulating some air between the house and the basement could lower that
and add desirable humidity to the house, with a little more heating fuel.
(Unless the home is 100% solar-heated :-) Outdoor air warmed to 70 F would
have 100Pa/0.748 = 16% RH. A 4"x1000ft^2 50K pound slab can slowly store
(0.03-0.01)50K = 1000 pints of water as the RH of the basement air rises
from 20 to 60%.
> - Circulate *in* hot air from outside (even if it is humid) to
> attempt to heat up the slab?
I don't think so, if it's more humid outside, in the absolute sense.
Nick
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Posted by jay on June 19, 2005, 3:58 pm
<<Do you have windows in the basement? Opening the windows will allow air
to circulate and remove some of the dampness and humidity.>>
Yes, there are windows, but opening them is not very convenient, and leaving
them open could worsen the problem if it is a humid day.
By the way, simply by keeping the blower motor of the heating/ac system
running continuously, the circulation of the air throughout the house, so
far, seems to be keeping the basement's relative humidity within the mid to
upper 50s (as opposed to sometimes creeping up into the mid 60s if the
blower motor is turned off). The humidity in the rest of the house is still
well below 50%.
Is a basement relative humidity level in the upper 50s too high if the goal
is to prevent potential mold/mildew in my finished basement?
Thanks,
J.
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Posted by on June 22, 2005, 12:12 pm
I am running my dehuminifer at 45% humidity level in my basement, and I
am also in Northern New Jersey.
I have two things that I need to mention about the use of a
dehuminifer:
1. Seem like its air moving capability is not that great even at high
fan speed. I have a feeling that it is only dehuminifing the adjacent
area. This "may" be a problem if the basement is partitioned in
multiple rooms or closets. Honestly, I am not sure about this. After
using it for two years, I don't have any mildew problem in my basement
(I had mildew problem in my basement before I started using the
dehuminifer). I guess it is doing something good in my basement despite
my concern about its coverage and despite the fact that my basement is
partitioned into two large rooms (with opening between rooms) and with
two closets.
2. Running dehuminifer can generate enough heat that we can feel
uncomfortably warm in the summer even with reduced humidity level. This
is especially bad if we have an exercise room in the basement. You
"may" need to add air-conditioning in addition to using the
dehuminifer. Still, using the dehuminifer should be the first choice
over the use of air conditoning to reduce humidity level because I am
under the impression that the air conditioner will stop as soon as the
room temperatur has dropped down to the pre-set level regardless if the
humidity level is reduced enough or not (and basement tends to be
cooler than the rest of the house to begin with; hence the air
conditioner will only run for a short while and probably will not
dehuminify enough).
Jay Chan
jay wrote:
> <<Do you have windows in the basement? Opening the windows will allow air
> to circulate and remove some of the dampness and humidity.>>
>
> Yes, there are windows, but opening them is not very convenient, and leaving
> them open could worsen the problem if it is a humid day.
>
> By the way, simply by keeping the blower motor of the heating/ac system
> running continuously, the circulation of the air throughout the house, so
> far, seems to be keeping the basement's relative humidity within the mid to
> upper 50s (as opposed to sometimes creeping up into the mid 60s if the
> blower motor is turned off). The humidity in the rest of the house is still
> well below 50%.
>
> Is a basement relative humidity level in the upper 50s too high if the goal
> is to prevent potential mold/mildew in my finished basement?
>
> Thanks,
>
> J.
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