what causes condensation to build up in my garage? I live in midwest &
weather isn't extreme. The garage is not insulated or heated. I am tired of
the rust on my tools. anyone know how to cure it?
Temperature differential and moist air. The garage is probably cooler than
the outside air right now. You bring in the warm outside air, close the
door and the moisture condenses. Leave the door open longer or heat the
garage a bit.
Meantime, protect your tools with something like Top Cote, Boeshield, etc.
In the winter, the slab gets very cold. In spring the outside air gets
warm (which holds more moisture), but the garage and especially the slab
is still cooler (which holds less moisture). If the cool slab does not
make it condense (like on a cold drink), the temperature drop at night
Be careful of ventilation. If the humidity ratio outside in grains of
moisture per pound of air is higher than the humidity ratio inside the
garage, you will not make things better. You would do yourself a favor
to add some heat instead. Also, don't use a kerosene heater or some
other UNVENTED fuel burnung heater, they add a lot of water vapor to
the air. If you have a cabinet that you keep your tools in, you can
add a heat lamp or a couple of light bulbs to warm the air inside the
cabinet. If the tools hang on a wall, a couple of heat lamps aimed at
the tools should help. Be careful not to get the lights too close to
wood or other flamable materials as you could start a fire.
Dew collects on grass when the grass temperature is less than
the dewpoint temperature of the air near the grass (which
increases with increasing humidity.)
Condensation appears on a tool in a garage when the tool temp
is less than the dewpoint of the garage air near the tool.
If you stir a glass of water with an ice cube with a thermometer,
it reads the dewpoint temp of the ambient air when condensation
(dew) first appears on the outside of the glass.
Td = Ta/(1-Taln(R)/9621), approximately, with temperatures in absolute
Rankine degrees and RH R in fractional form. For instance, 70 F (Ta
= 70+460 = 530 R) air at 50% RH (R = 0.5) has Td = 530/(1-530ln(0.5)/9621)
= 510.5 R, ie Td = 510.5-460 = 50.5 F.
Nonono. The dew point temp goes UP with increasing RH.
You DO have a Casio fx-260 solar scientific calculator, no?
R degrees = F degrees + 460.
R = RH/100.
With RH = 60%, R = 0.6, so Td = 530/(1-530ln(0.6)/9621) = 515.5 R,
ie Td = 515.5-460 = 55.5 F.
PS: The price of a standard basement Humidex is $1095, installed.
Loren says they have a 1 year performance guarantee, ie you
can get your money back after 1 year if you don't like it. And
she says it works better in houses with AC. But moving air from
near the basement floor upstairs would be more efficient than
moving it outdoors and moving more outdoor humid air indoors,
in a house with AC.
The humidex is one of the dumbest ideas that I have seen in years. I
went to their web site and found it is a basement exhaust fan. It
sucks cool air conditioned air from the house, through the basement and
then blows it outside. Now the house is under a negative pressure and
outside air will come in to the house to replace the exhausted air.
If the humidity ratio of the outside air is lower than the humidity
ratio of the basement air, there is no point in getting the house air
involved, it would be better to blow basement air outside to be
replaced with dry air from outside. You may as well run the AC with the
windows open. Or run the heat in the winter with the windows open.
If the humidity ratio of the outside air is higher than the basement or
crawlspace air, you are adding a lot of moisture to the house and
adding load to the AC system, increasing electric bills in the process.
You could start growing mold in the house. The Humidex just moves the
problem from the basement to the house. Bad Idea.
Buy a dehumidifier instead. In humid climates the Humidex is a
disaster about to happen. In dry climate areas, it is just a waste of
Dumber than a dehumidifier that uses lots of electrical energy?
It sucks up basement air from near the floor and exhausts it
from the house when the basement air exceeds, say, 60% RH.
If the house is air-conditioned.
Sure, if the house is being heated or air-conditioned.
Does the Humidex add more than 5 cents/pint to AC and heating bills?
That depends on the weather. Moving basement air upstairs would use
less energy in a house with AC. A dehumidifier would use more, since
it adds to the AC load.
A little extra ventilation as needed isn't so bad in wintertime. Moving
cold air in from a basement window seems better than moving warm air
down from upstairs. It might come in through a concentric duct inside
the exhaust duct. Moving basement air out through an air heater on a
south wall and back to the basement after condensation (with an airflow
high enough to avoid freezing) could use less energy than ventilation.
My newish Kenmore dehumidifier acts like a heat pump with a 1.6 COP, ie
for every kWh of electricity consumed it condenses 2.047 pounds of water,
which makes 0.6 kWh (2047 Btu) of sensible heat. Condensing a pound of
vapor requires 1/2.047 = 0.4885 kWh worth 4.9 cents at 10 cents/kWh. If
1 kWh consumed offsets 1.6 kWh of electric resistance heat in winter, the
net energy profit for removing a pound of water vapor with a dehumidifier
is 0.6/2 = 0.3 kWh. If the house has a heat pump or gas or oil heat,
the "profit" is likely a net loss.
NREL says the outdoor humidity ratio wo = 0.0025 pounds of water per
pound of dry air on an average 30 F January day near Phila. Indoor air
at 70 F and 60% RH has wi = 0.009476, so removing a pound of water by
ventilation requires moving 1/(wi-wo) = 143 pounds of fresh air through
the house. Warming it from 30 to 70 F requires 0.24x143(70-30) = 1376 Btu,
ie 0.4 kWh. A 2470 cfm 90 W fan can move 143 pounds in 143/(2470x0.075)
= 0.77 minutes, consuming 90x0.77/60 = 0.001 Wh. So winter ventilation
uses less electricity than the dehumidifier, but there's no desirable
heat pump effect.
Mold seems unlikely to me, if the AC works and the Humidex shuts off when
the basement RH drops to 60%.
Maybe, in wintertime. But most houses don't need dehumidification then.
That's a concern, in a house without AC. I can picture the Humidex pumping
humid outdoor air into a basement with a cold slab that keeps condensing
water out of the air until the slab warms to the dewpoint, when condensation
would stop, but that might take a long time and make a big pool of water
which doesn't disappear until winter. IMO, these things could use better
controls, at least, and more competition, in light of their price.
Herbach and Rademan (800) 848-8001 http://www.herbach.com sell a nice
$4.95 Navy surplus humidistat, their item number TM89HVC5203, with a
20-80% range, a 3-6% differential, and a 7.5A 125V switch that can be
wired to open or close on humidity rise...
For any given amount of moisture in the air, dew will form at a specific
temperature. The more moisture in the air, the higher the temperature where it
will begin to form. It varies directly with the ambient humidity.
Look at the weather report for your area on any given day and see what the
dewpoint is reported to be; it'll be different every day. Then keep your garage
warmer than that number.
As a pilot, I've always been leery of flying to an airport where the
temperature/dewpoint spread was two degrees or less; fog is almost always going
to be a consideration. It doesn't take much for a forecast to be off a couple
of degrees... just enough for the temp and the dewpoint to become one and the
same. The result for me: poor visibility. For you: rusty tools.
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