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Posted by jay on June 17, 2005, 5:47 pm
I live in Northern NJ. I'm beginning to monitor humidity levels in my
basement to determine whether or not I need a dehumidifier. Today, I put a
hygrometer and the relative humidity of my basement was around 66%. Today
was not warm enough to use AC, but I decided to turn the blower motor of my
furnace/AC system on, and since there are return ducts in the basement, the
added circulation caused the basement humidity to drop to around 59% after
leaving the fan on for an hour or more. If I shut the fan off for an hour
the humidity would rise into the mid 60s again. The humidity at the rest of
the house was still at the low 40% range.
If I can keep the basement humidity below 60% by simply leaving the fan on,
do I really need a dehumidifier?
Does leaving the blower fan on all the time use up too much electricity or
cause blower motor to wear out very quickly?
By the way, my basement is finished, and I don't want mold problems. If
you think I should get a dehumidifier to further reduce humidity, then I
think the only convenient logical place to drain the condensation would be
to install a T fitting into the existing narrow PVC A/C condensation drain
pipe. (and presumably some dehumidifiers have the ability to pump the
condensation upward through a tube which I would connect to the T fitting.
If I want to avoid having to empty out tanks, then is the setup I just
described a good setup?
(If so, then hopefully basement humidity would not be a problem during the
heating season, because the only practical location is within the furnace
room, and since the furnace room gets hot/dry when the gas furnace is
running, the dehumidifier would not function correctly during the winter
months. Presumably I would only need to use the dehumidifier in the warmer
months)
Thanks,
J.
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Posted by Hopkins on June 17, 2005, 7:02 pm
Uh, I wouldn't run the blower all the time.
Yeah, dehumidifiers are typically necessary during only the warm
months.
Where does the "AC condensation drain" go? I'm guessing there's no
floor drain.
The typical dehumidifier often has a small hose to allow water to drain
without emptying the tank, but there's no pump to pump the water out.
>From what you've written, a T fitting shouldn't be a problem but it
needs to be close to the floor. Of course, you'll have to figure a way
to seal the hose-to-T connection.
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Posted by Harry Everhart on June 17, 2005, 7:09 pm
> By the way, my basement is finished, and I don't want mold problems. If
> you think I should get a dehumidifier to further reduce humidity, then I
> think the only convenient logical place to drain the condensation would be
> to install a T fitting into the existing narrow PVC A/C condensation drain
> pipe. (and presumably some dehumidifiers have the ability to pump the
> condensation upward through a tube which I would connect to the T fitting.
> If I want to avoid having to empty out tanks, then is the setup I just
> described a good setup?
I have a dehumidifier running in my Pennsylvania home basement in the
summer. If you have a clothes washer down there - you can run the drain
tube into the washer drain tube. That way you will not to empty the
tank. You will have to mount the dehumidifier high enough to drain by
gravity.
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Posted by twfsa on June 17, 2005, 7:29 pm
I run a dehumidifier in the summer as it seem to take the musty smell out of
the basement and mine is finished, and there is nothing wrong with running
the fan on the furnace constantly, mine runs 24-7 365.
Tom
>I live in Northern NJ. I'm beginning to monitor humidity levels in my
>basement to determine whether or not I need a dehumidifier. Today, I put a
>hygrometer and the relative humidity of my basement was around 66%. Today
>was not warm enough to use AC, but I decided to turn the blower motor of my
>furnace/AC system on, and since there are return ducts in the basement, the
>added circulation caused the basement humidity to drop to around 59% after
>leaving the fan on for an hour or more. If I shut the fan off for an hour
>the humidity would rise into the mid 60s again. The humidity at the rest
>of the house was still at the low 40% range.
>
> If I can keep the basement humidity below 60% by simply leaving the fan
> on, do I really need a dehumidifier?
>
> Does leaving the blower fan on all the time use up too much electricity or
> cause blower motor to wear out very quickly?
>
> By the way, my basement is finished, and I don't want mold problems. If
> you think I should get a dehumidifier to further reduce humidity, then I
> think the only convenient logical place to drain the condensation would be
> to install a T fitting into the existing narrow PVC A/C condensation drain
> pipe. (and presumably some dehumidifiers have the ability to pump the
> condensation upward through a tube which I would connect to the T fitting.
> If I want to avoid having to empty out tanks, then is the setup I just
> described a good setup?
>
> (If so, then hopefully basement humidity would not be a problem during the
> heating season, because the only practical location is within the furnace
> room, and since the furnace room gets hot/dry when the gas furnace is
> running, the dehumidifier would not function correctly during the winter
> months. Presumably I would only need to use the dehumidifier in the
> warmer months)
>
> Thanks,
>
> J.
>
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Posted by on June 18, 2005, 6:49 am
>I live in Northern NJ. I'm beginning to monitor humidity levels in my
>basement to determine whether or not I need a dehumidifier. Today, I put a
>hygrometer and the relative humidity of my basement was around 66%. Today
>was not warm enough to use AC, but I decided to turn the blower motor of my
>furnace/AC system on, and since there are return ducts in the basement, the
>added circulation caused the basement humidity to drop to around 59% after
>leaving the fan on for an hour or more.
Not a big change. Did you warm the basement?
Removing moisture from materials can take a long time.
>...The humidity at the rest of the house was still at the low 40% range.
>
>If I can keep the basement humidity below 60% by simply leaving the fan on,
>do I really need a dehumidifier?
Maybe not.
>Does leaving the blower fan on all the time use up too much electricity or
>cause blower motor to wear out very quickly?
I'd say so... maybe 400 watts, $400/year.
Then again, you might store dryth in the basement on dry days.
Kurt Kielsgard Hanson's 142 page catalog of sorption isotherms
as LBM technical report 162/86 under
http://www.byg.dtu.dk/publications/reports.htm
says concrete stores about 1% moisture by weight as the RH of the
surrounding air increases from 40 to 60%, and it weighs about 150 lb/ft^3,
so a 4"x1000ft^2 50K pound floorslab might store 500 pints of water as
the basement RH increases from 40 to 60%. Mold forms in about 2 weeks,
above 60% RH.
The catalog also says the equilibrium moisture content of some woods
is about 30% by weight of the RH of the surrounding air, so a 25 lb
cubic foot of dry hem-fir might weigh 28 pounds in 40% air and 30 at 60%,
after storing 2 pints of water. Paper and clothing also store water.
The calc below says outdoor air is dry enough to keep a house below 60%
at 70 F for all but 360 hours in NREL's TMY2 Typical Meteorological Year
in Phila, with at most 75 "wet hours" in a row near the end of July.
20 PH=.6*EXP(17.863-9621/(70+460))'house vapor pressure ("Hg)
30 WH=.62198/(29.921/PH-1)'house humidity ratio
40 DAYSTART=150'display start time (days)
50 DS=DAYSTART*24'display start time (hours)
60 RANGE=3000'dISPLAY RANGE (HOURS)
70 LINE (0,0)-(639,349),,B:XDF=640/RANGE:YDF=3.88
80 FOR TR=60 TO 80 STEP 10'temp ref lines
90 LINE (0,349-YDF*(TR-10))-(639,349-YDF*(TR-10)):NEXT
100 CFM=2470'whole house window fan cfm (Lasko 2155A)
110 OPEN "ecayear" FOR INPUT AS #1:LINE INPUT#1,H$
120 FOR H=1 TO 8760'hours of typical (TMY2) year
130 INPUT#1,MONTH,DAY,HOUR,TDB,WIND,TDP,IGLOH,SS,WS,NS,ES
140 PA=.6*EXP(17.863-9621/(TDP+460))'ambient vapor pressure ("Hg)
150 WA=.62198/(29.921/PA-1)'ambient humidity ratio
160 PSET(XDF*(H-DS),349-YDF*(TDB-10))
170 'PSET(XDF*(H-DS),349-YDF*(TDP-10))
180 IF WA<WH THEN WETSTRING=0:GOTO 230'dry hour
190 WETHOURS=WETHOURS+1'accumulate wet hours
200 WETSTRING=WETSTRING+1'accumulate wet string length
210 IF WETSTRING>WETMAX THEN WETMAX=WETSTRING'measure max wet string length
220 LINE (XDF*(H-DS),290)-(XDF*(H-DS),300)'mark wet hours
230 IF DAY=1 AND HOUR=.5 THEN LINE (XDF*(H-DS),349)-(XDF*(H-DS),345)
240 NEXT H
250 PRINT WETHOURS,WETMAX
wet hours per year: 360
longest wet string: 75
Nick
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