Reducing humidity with a fan: top or bottom?


I have two vent fans in my bathroom; and after a long, steamy shower, I’m still getting water and stains on my walls. How can I fix this problem? -Phil

Hi Phil,
You can’t expect prolonged exposure to a room full of steam not to condense on your bathroom walls, so start by cutting back on the length of your shower and lower the water temperature. A bathroom vent fan isn’t designed to remove all steam in a matter of seconds; so you have a confined space that’s filling with steam faster than one, or even two, fans can pump it out.

Here are some tips to improve the performance of your exhaust fan in removing moisture from the bathroom:

Turn the vent fan on before you start your shower, and let it run for 20 minutes after you finish your shower. Installing a timer switch or humidity sensing fan is a good way to make sure you run the fan long enough to clear the air after a shower. Make sure the exhaust fan vents outside through a wall or roof. While nonventing...
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It’s important you keep the climate of your grow room at the right level, but should this change it’s important you know how to lower humidity in a grow room so that your plants can thrive.

Why Humidity is Important

Plants breathe like humans do but in order to breathe they require a specific level of humidity. Plants create this humidity by breathing out water vapour – known as transpiration – but if it is too humid the plant will not breathe properly and it will ultimately not grow very well. The level of humidity also affects how much water they take in and thus how many nutrients they take in.

If it’s too humid, plants will try to breathe water vapours back in from the air and will drink less water from the reservoir. This can also have a negative effect on the plants growth because it’s not taking in the nutrients needed to develop. Also, bacteria tends to develop and thrive in more humid grow chambers and this can harm your plant.

How to Lower...

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Humidity and condensation

Humidity and condensation can compromise building occupants' health and comfort, damage interior finishes, and raise heating costs.

On this page:

relative humidity (RH)reasons for high humiditycontrolling humiditymaintaining a comfortable humidity rangecondensation.

Relative humidity (RH)

Air usually contains water vapour, the amount depending primarily on the temperature of the air. Warm air can hold more moisture than cold air, so as the air temperature falls, the maximum amount of water the air can hold also falls.

The ratio of water vapour in the air to the maximum amount of water vapour the air can hold at a particular temperature is expressed as relative humidity (RH). For example, a RH of 30% means that the air contains 30% of the moisture it can possibly hold at that particular temperature.

When air can hold no more moisture at a given temperature (i.e. the RH is 100%), the air is said to be...

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A little condensation is not bad. You will always get some with shades and drapes the limit circulation.

You might have a house that is too tight. Mine has a fresh air intake that feeds the furnace room. It is not sealed so I don't know how it effects the inside humidity. From experience, I know that even outside cold air at a high humidity PERCENTAGE does not really have much moisture in it and can dry out the interior when it gets inside. - A far cry from the southern winter air.

My furnace (Bryant) is a new 80% (could not justify a 90% model even in Minnesota), but it does have what is advertised as a "variable speed" D.C. fan. It certainly has a mind of its own. I am so pleased with the temperature uniformity (2 story with open split entry) and summer humidity I get by running it 100%, I have not bothered with the details.

Dehumidifying below about 40% will cost you, plus you may have to bump up the thermostat a bit because of the...

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Re: Basement Moisture - Dehumidifier Out, Vent Fan In?


The negative pressure will pull air through any crack and crevice available, thusly creating circulation and fresh air intake. However, it's probably not on the top 5 list of ways to do so.

There is a cold air return on the system in my mothers basement, which helps emensly with the humidity level. There is no supply down there, but it draws warm air down the stairs from a nearby register. When the new furnace was installed, they panned over the return hole in the basement. It caused the remaining 2 returns on the main floor to become very noisy, starving the system. It also created a noticable difference in...

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In coastal areas of the U.S., it’s common to have houses built over closed crawlspaces. This is partly because the water table is often so high that if you build a basement under a house, it’s like having an indoor swimming pool. About 30% of all new houses built in the southern part of the U.S. are built on crawlspaces. In South Carolina, the number is more like 70%.

The trouble with crawlspace construction is that it’s more likely to have mold and wood rot problems than other types of construction. Both of these problems are types of fungal growth.

If mold is growing on the wood in the crawlspace, even in spots, you have problems. If it’s a white mold, it’s usually a surface mold, but consider it a sign that humidity levels are too high. White mold usually doesn’t cause real damage to the wood; however, if you see black or brown mold, that’s rot fungus: Structural damage is occurring that could require replacement of wood members. Immediate action is...

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