basement humidity

[Pete Dorr]

All

I'm trying to come up with a better way than traditional dehumidifiers to keep my basement at a reasonable humidity level. With 2 dehumidifiers running the humidity guage says 60-70% which I believe is high.

I also believe that a dehumidifier is probably not the most economical thing to run.

I've googled and found some suggestions that by using a blower to blow out the air from the basement might be a good option.

Perhaps something like the following blower with attached hose (venting to outside) would do the trick. If we keep the basement door open it should let the less humid air from upstairs vent into the basement.

http://www.northerntool.com/images/product/images/177770_lg.gifhttp://www.northerntool.com/images/product/images/177772_lg.gif

Does anyone have any comment on this idea or have other ideas.

Thanks
Pete

[Figment]

What's the source of the moisture?

[Pete Dorr]

Figment - good question

It's typical Cape Cod -- high humidity basement

As far as I can tell groundwater is not an issue.

Given the coolness of the air in the basement I'm half tempted to just push the air up the existing heating ducts and cool off the house. But then I'd just be pushing humid air into the living spaces.

I'd like to eventually use this basement as a fun zone (pool table/tv/...)

Pete

[ssor]

Bring in 80 degree outside air and ventilate the space. As long as it remains cool and the dew point is higher than the surface temperatures in the basement you will get condensation. If you can warm the contents of the room you will be able to get it dry. Your best source of heat is the summer air outside.

[Greg Nolan]

Brining warm, humid air (there is no other kind of warm air on the Cape in the summer) in from outside will often make the problem worse, unless you actually bring in enough warmth to heat the basement.

Basements are cool because they are underground -- the reason caves are cool and wine is cellared is that the earth is a great heat sink.

The relative humidity of air will rise when it is cooled by the basement walls -- in other words, the warm air will feel, and be, relatively damper when brought into the basement and cooled.

You will have to circulate a great deal of very warm air through to heat the basement, and you will have to stop that circulation in the evening, when the outside air is cooler (and relatively damper).

Of course, heating the basement in this way will also likely warm up the house above it -- something you may not want.

[Pete Dorr]

update

I moved the humidity gauge to the second floor and it now reads 52% which is down from 70% that was in the basement

it's also 80 degrees upstairs

[Bruce Hooke]

If the basement air is about 70 degrees then according to the wizard on this website: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html it looks to me like air in the basement and upstairs both have the same absolute amount of moisture in the air, the only difference is that because the basement is cooler the relative humidity is higher there. If the basement is warmer than 70 degrees then there is more absolute moisture in the air down there, which means there is some actual source of moisture in the basement, at least if I am thinking about this right.

[Pete Dorr]

I will measure temp in the basement and post in a bit

[GregH]

Move the fan setting on your thermostat from auto to ON. Leave it there all the time. That way, the air in your entire house will be continually circulated, evening out both the temp and humidity. My furnace fan runs continuously all year 'round.

[johngsandusky]

I live on Long Island, similar conditions. When I had a basement I kept it dry by opening the windows whenever a NW was blowing dry air over the land. Close them in rain, fog, or SW.

[Pete Dorr]

70 degrees in basement

we do have a few windows and I can try opening them on hot/dry days to see if that helps. Obviously that's the cheapest method.

With regards to running the hvac fan. I believe that the air in the basement is not cycled as the air is pushed to the upstairs rooms and then pulled back down through the returns. If I cut a hole in the return duct at the furnace and opened that up it would certainly draw from the basement. I could close that and tape it for winter or when we actually want to use the AC.

Pete

[Tom Robb]

Just my personal opinion but I think basements as living spaces is a terrible idea. Sooner or later thay get wet or flooded and the finish and nice stuff is ruined. It happens with disheartening regularity. Besids if any work needs to be done on plumbing, wiring, or whatnot all that nice finish stuff is in the way and usually the ceiling is too low unless you're very short.
And Bruce is probably right. You've probably got water down there somewhere.
I'm in N.E. Ohio where if you have a basement, it's wet or you have a sump pump and dehumidifier. Heavy clay soil coutresy of the last glaciers - just like Long Island and Cape Cod.

[Bruce Hooke]

70 degrees in basement

Bingo. So the basement is not adding any moisture to the air, it is just cooler down there so the relative humidity is higher. So, your basic choice, as others have pretty much said, is to either:

1. increase the temperature in the basement -- get it to 80 and the humidity will match the rest of the house, OR

2. fight an uphill battle to try to get moisture out of the basement air by running some sort of dehumidifier (or air conditioner), but as soon as new air filters in you will have to reduce the moisture in it too.

Various means of getting more air to circulate through the basement is basically pursuing option 1 above. Note that if you move the air from the basement to the rest of the house it will raise the humidity in the rest of the house until that air warms up.

Before you go too far in trying to dry out the basement air to make it more livable...have you tested for radon? It would be a shame to go to lots of work to get better air down there only to discover that you have a radon problem, and it would be particularly unfortunate to take what might be bad air down in the basement and put it into the rest of the house where you would breath it all the time!

[ssor]

If you have adequate ventilation radon won't be a problem. If the world is not musty and you open the basement to the world and exchange the air with it your basement won't be musty either. Closed spaces with inadequate ventilationa re cold damp and musty.

[jackster]

Pete,
Just my opinion, but Bruce's information makes the most sense to me. If you want to use the basement as a living area, it is important to check if any moisture is entering through the concrete. To do this, tape a patch of plastic on the floor and one on the wall. If condensation forms UNDER the plastic, then moisture is coming through the concrete. If moisture forms on TOP of the plastic, it is from the humidity in the air. I wouldn't worry so much about the relative humidity and the difference with upstairs, as long as no moisture is coming in through walls or floor. If you were to lower the temp upstairs, the relative humidity would also increase, which is desirable. Again, just my two cents.
Good luck with your project, If every thing works out you have some found living (recreation) space.

[jackster]

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Technical Bulletin #10

Dew Point
Definition: Dew Point is the temperature at which condensations forms.


To determine the Dew Point from the charts below, find the temperature of the air in question on the left side of the table. Next, locate the relative humidity of the air in question across the top of the table. The intersection of these two numbers in the matrix identifies the temperature at which Dew Point is reached.

When air comes in contact with a surface that is at or below its Dew Point temperature, condensation will form on that surface.


Example:
If the temperature in a facility is 75º F (24º C) and the relative humidity is 35%, the intersection of the two shows that the Dew Point is reached at a temperature of 45º F (7º C), or below. This means that moisture vapor in the 75º F / 35% RH air will condense on any surface that is at or below the Dew Point temperature of 45º F.

This example could represent the inside of a building that is 75º F and 35% RH during the day. At night the outside temperature drops. It is not likely that the inside air of the building will cool from 75º F to 45º F, but it is quite possible that the framing and any exposed exterior surfaces will reach the Dew Point temperatures, creating condensation.





Air Temperature in Degrees Celsius

Air

Temp °C
% Relative Humidity

100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10
43 43 42 41 40 39 38 37 35 34 32 31 29 27 24 22 18 16 11 5
41 41 39 38 37 36 35 34 33 32 29 28 27 24 22 19 17 13 8 3
38 38 37 36 35 34 33 32 30 29 27 26 24 22 19 17 14 11 7 0
35 35 34 33 32 31 30 29 27 26 24 23 21 19 17 15 12 9 4 0
32 32 31 31 29 28 27 26 24 23 22 20 18 17 15 12 9 6 2 0
29 29 28 27 27 26 24 23 22 21 19 18 16 14 12 10 7 3 0
27 27 26 25 24 23 22 21 19 18 17 15 13 12 10 7 4 2 0
24 24 23 22 21 20 19 18 17 16 14 13 11 9 7 5 2 0
21 21 20 19 18 17 16 15 14 13 12 10 8 7 4 3 0
18 18 17 17 16 15 14 13 12 10 9 7 6 4 2 0
16 16 14 14 13 12 11 10 9 7 6 5 3 2 0
13 13 12 11 10 9 8 7 6 4 3 2 1 0
10 10 9 8 7 7 6 4 3 2 1 0
7 7 6 6 4 4 3 2 1 0
4 4 4 3 2 1 0
2 2 1 0
0 0



Example: Read the air temperature in the left hand column and the humidity at the top of the chart. If the temperature of the storage unit is 75ºF (24º C) and the relative humidity is 35%, the intersection of the two shows the dew point of the area to be 45ºF (7ºC). If the metal coming in is below 45ºF (7ºC), water will condense on the metal.



Air Temperature in Degrees Fahrenheit

Air

Temp °F
% Relative Humidity

100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10
110 110 108 106 104 102 100 98 95 93 90 87 84 80 76 72 65 60 51 41
105 105 103 101 99 97 95 93 91 88 85 83 80 76 72 67 62 55 47 37
100 100 99 97 95 93 91 89 86 84 81 78 75 71 67 63 58 52 44 32
95 95 93 92 90 88 86 84 81 79 76 73 70 67 63 59 54 48 40 32
90 90 88 87 85 83 81 79 76 74 71 68 65 62 59 54 49 43 36 32
85 85 83 81 80 78 76 74 72 69 67 64 61 58 54 50 45 38 32
80 80 78 77 75 73 71 69 67 65 62 59 56 53 50 45 40 35 32
75 75 73 72 70 68 66 64 62 60 58 55 52 49 45 41 36 32
70 70 68 67 65 63 61 59 57 55 53 50 47 44 40 37 32
65 65 63 62 60 59 57 55 53 50 48 45 42 40 36 32
60 60 58 57 55 53 52 50 48 45 43 41 38 35 32
55 55 53 52 50 49 47 45 43 40 38 36 33 32
50 50 48 46 45 44 42 40 38 36 34 32
45 45 43 42 40 39 37 35 33 32
40 40 39 37 35 34 32
35 35 34 32
32 32


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t figure is the dew point..

[TMny]

>half tempted to just push the air up the existing heating ducts and cool off the house

Probably not good idea insofar as the moisture-laden air might condense in your ducts ... and if the moisture included salt spray , the salt/chloride-ion-residue would remain on the metal surface , and it would chronically adsorb moisture from adjacent air , and corrosion cell would result. In winter temperate latitudes prevailing winds are NW {Canadian Polar Dry} ; in summer SW wids prevail {nor dry, and frequently salt-laden}.
* *
I believe a properly configured "air-to-air" heat exchanger might transfer the coolness from below upstairs ....