Author Topic: Dehumidification... is that a word? It is now.  (Read 1650 times)

Britan

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Dehumidification... is that a word? It is now.
« on: September 10, 2018, 09:47:40 AM »
I live in a feckin swamp. Ok not literally. I just live next to one. In a swampy region.

Our house has had a few (thankfully small) incidents of mold growth limited to drywall that we have addressed. Some were from leaks, some I think from just high summer humidity (70-75% average). Thankfully we are not as bad as a few of the houses around us where the owners are not as conscientious about checking for mold.

The general advice seems to be to keep your house humidity below 60% (ideally 30-50%) to avoid mold growth. However we have struggled to get our house below 60% during the summers.

One option is to use the AC. However I generally set it to 80, and just open windows if itís below 80 outside. Helps with electric bills but it means that the inside humidity = outside humidity, which again is usually above 65%. And it doesnít make sense to run the dehumidifier if you have all your windows open to the humid outdoors, does it?

We have a dehumidifier in the basement, as itís the most humid part of the house and the area weíve had the most recurring mold issues. However even that struggles to get humidity to even 60%, and it also spits out hot (dry) air, heating our space in the middle of summer, causing the AC to run. Arg!

I just found a small section of mold again on the second floor (in a room that is generally pretty humid) and itís been taken care of. However Iíd like to do something to generally keep humidity down in this house, especially during the shoulder seasons when I would rather open windows than run the AC. Finding and remediating mold every couple years adds up... A dehumidifier in each room seems like a pain to empty. Is a whole house dehumidifier worth it? Do I just need to suck it up and constantly run something electrical to prevent mold growth?  Should I just move back to the desert? ;)

HipGnosis

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Re: Dehumidification... is that a word? It is now.
« Reply #1 on: September 10, 2018, 10:42:49 AM »
Yes, a dehumidifier is what you need when the temps are fairly low and the humidity is fairly high.
It sounds like you need one in your living area in addition to your basement.
A dehumidifier puts out a bit of warm air; but it's also putting out a bit of cool air - so it's (theoretically) a null effect. 
A dehumidifier is much cheaper to run than AC.   

Takk

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Re: Dehumidification... is that a word? It is now.
« Reply #2 on: September 10, 2018, 12:30:53 PM »
Two ways to reduce water in the air (humidity): Chemically and cooling.

cooling reduces it via lowering the temperature of the air to below the condensation point (think water on the outside of a cold glass) and collect the water. the rest of the process is whatever it wants to do with the heat on the other end of the cold coils. Usually put it back into the air, interior or out.  (Ex: Your house AC system, or a standard plug-in dehumidifier)

Chemically is dehumidification by using a dessicant material (think how salt absorbs water from the air and cakes up, reduces water in the air) (Ex: Damprid)

Pick one, I live in Florida, USA. and it's humid all the time, sealing, closing windows and keeping it conditioned is the best solution to keep humidity down. If you want to open airways, pushing dry air (cold) into the rooms that are open to the environment will lessen the humidity, but it is not a great method with a big ol' leak A.K.A. window open in the room. Suggestion: Measure humidity outside, only open windows if it's lower than 55% RH. close windows if it's more. This basically makes you do a manual economizing cycle on your house.

MDM

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Re: Dehumidification... is that a word? It is now.
« Reply #3 on: September 10, 2018, 02:29:13 PM »
One option is to use the AC. However I generally set it to 80, and just open windows if itís below 80 outside. Helps with electric bills but it means that the inside humidity = outside humidity, which again is usually above 65%. And it doesnít make sense to run the dehumidifier if you have all your windows open to the humid outdoors, does it?
No, it doesn't.

Keeping the windows closed when the outside humidity is high is probably your best bet.  You may pay a little more for A/C in the short term, but recoup that in lower long term cost of ownership.

fuzzy math

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Re: Dehumidification... is that a word? It is now.
« Reply #4 on: September 10, 2018, 03:40:13 PM »
Buy another dehumidifier. Run it. Run your ac.
Being so frugal that you fill your house with mold to save money isnt frugal or cheap. It will cost you more and it can affect your health.


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light switch

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Re: Dehumidification... is that a word? It is now.
« Reply #5 on: October 07, 2018, 09:31:15 AM »
Is it possible there is a fundamental flaw in the house design, that encourages this?   It's my understanding that just about all of the houses built after AC was introduced ignored basic "rules" of pre AC houses.  If it's possible to do some renovating in order to make the house breath more efficiently, would the cost of that be easier to take than however much an additional dehumidifier would cost to run for the rest of your life?  I doubt any of us are interested in living in Nipa huts, but I don't think they have any mold issues, and are located in what I'd consider to be extremely humid environments. 

My recommendation is to buy and run another dehumidifier.  But I wonder about alternative solutions that might be more efficient over the long term.

1: Cold showers instead of steaming hot showers.
2: More airflow...like a lot more airflow.  As opposed to sealing yourself in, and trying to "control" the conditions inside to the nth degree.
3: Strategic placement of shade trees.
4: Strategic placement of windows.

I understand the house is already built and bought, so maybe none of those things, except the showers are even options.  But it might be worth looking at. 

Goldielocks

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Re: Dehumidification... is that a word? It is now.
« Reply #6 on: October 08, 2018, 01:27:12 AM »
Condensation forms where warmer / moist air hits cooler objects.   Mold tends to form because of areas of active condensation.  (cooler areas like basement walls / concrete behind walls).

One option is to ensure your rooms (walls) are at the same temp or above the temp of the moist air coming in. 

 Try to figure out why the condensation is happening in the upper living area.   We had it behind a sofa pushed up against the wall (ok, a different problem, the condensation was forming ice between the insulating sofa and the wall, which is what caused our mold, but you get the idea, the water is forming where it is cooler with less airflow to remove higher humid air in that region).

expatartist

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Re: Dehumidification... is that a word? It is now.
« Reply #7 on: October 08, 2018, 05:05:51 AM »
Fellow humid climate-dweller here, commiserating with your situation. We're at 80%+ much of the year, 65% or lower feels positively dry. I live in an 'old' apartment building in Hong Kong, built cheaply in the mid-20th century, with natural cooling via airflow and generally not much mold though not well built. Now we've all got aircon units and I'll use mine if necessary since my flat was subdivided from a larger one and heat can get trapped. Still when we have the hallway door open, air from the rooftops whooshes down and clears out heat straight away.

This year we had several weeks of unrelenting heavy rain. I got mold inside all my wooden furniture, and under my kitchen sink. It would've been worse but I'd placed open jars of salts inside which absorbed quite a bit of water. Chunky salts like kosher and himalayan, left over from a botched bath bomb project. Also lots of bamboo charcoal which helped dehumidify and deodorize too. Frequently use a HEPA filter for air purification as well. I tend to keep windows sealed while out during the day (open if home, but shaded) and sealed at night with dehumidifier on due to the pests in my neighbourhood, and have an exhaust fan running 24/7. I try not to have aircon and dehumidifier running at the same time, it uses up so much energy but sometimes can't be helped. Generally I try to stay in tune with weather outdoors and as long as there's a fan, find a dry room more comfortable even in hot weather and don't need to cool things down.

It sounds like your house may be made of various materials, some of which could be exacerbating the problem and there's only so much you can do. Interesting to hear about interior temperature changes as sources of dampness. Best of luck!

Fresh Bread

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Re: Dehumidification... is that a word? It is now.
« Reply #8 on: October 08, 2018, 05:24:13 AM »
I live in a humid area also and was constantly dealing with mould. We've had a very pricey heat recovery ventilation system installed that seems to have helped considerably (no more condensation on the windows) although ask me again when it's been tested in our summer. There's a boiler sized unit in our laundry that sucks air out of the bathroom and kitchen and pumps it back into the living areas. The heat recovery function keeps it almost the same temp as it transfers in and out. Supposedly it has low power usage (haven't had outlet quarterly bill yet). Prior to this we just had an AC unit in one room and a portable dehumidifier that we never remembered to use whereas this system runs constantly.

I was also told (on this forum I think!) that mould will feed on dust so keeping surfaces clean helps. My ventilation system also has a filter that helps with dust, we have far less now.

FLBiker

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Re: Dehumidification... is that a word? It is now.
« Reply #9 on: October 08, 2018, 11:00:34 AM »
I also live somewhere humid (Florida).  Our first year in our house, we ran the AC minimally, and everywhere something plastic was lying on the floor there was mold.  We also got some on some particle board (ie the back of furniture).  We got rid of all that stuff, and since then we run the AC a bit more.  We still keep it pretty high (78 when home, 80 when not home) but we never just turn it off and open the windows during humid months (ie from May to October).  We also have two dehumidifiers -- one we use in the laundry room (where we hang dry) and the other in our bathroom (which we run post showers).  We haven't had any mold issues, and our electric bill is still very reasonable.

NathanP

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Re: Dehumidification... is that a word? It is now.
« Reply #10 on: October 08, 2018, 01:40:05 PM »
My findings from living in the high-humidity southeast (Georgia, North Carolina, and Florida) is that you have three options:
  • Leave the windows open all the time (airflow will prevent mold)
  • Keep windows closed and use the AC
  • Dehumidifier

Currently in North Carolina we are stuck in a mild temperature, but extremely high humidity phase which is pushing my home's interior humidity up near 70%. Since I don't have a dehumidifier my best option is to lower the temperature in the home lower than I would like. Also, be aggressive with your use of ventilation fans for all baths/showers/cooking. Soon the temps and humidity will drop allowing for open windows and fresh air!

bigdoug03

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Re: Dehumidification... is that a word? It is now.
« Reply #11 on: October 09, 2018, 10:32:10 AM »
I'm a big fan of heat pump hot water heaters, in part because of the "free" cooling and dehumidification they provide. If you have an older electric model you may look into upgrading.

Mine saved me $30 a month on the electric bill, and also provided enough dry air that I don't have to run a dehumidifier in the basement anymore. Win win!

aetherie

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Re: Dehumidification... is that a word? It is now.
« Reply #12 on: October 09, 2018, 11:44:13 AM »
Maybe the people in this thread can help me...

Spouse and I just spent our first summer in a new apartment with no AC. We managed the temperature fine with box fans and opening windows at night, but we didn't realize how humid it was getting.  Then a few weeks ago I noticed some thin, fuzzy, blue-white spots on part of an ottoman... one armchair... the curtains... the particle board pantry shelves... SO GROSS. And probably slowly giving us cancer. I tried spraying the furniture with a vinegar/water mix, wiping off, and pointing a fan at it. That helped for a few days but the mildew (?) keeps coming back.

So we bought a dehumidifier and it's doing its thing. Assuming we're able to keep the humidity under control from now on, what should we do about all the mildewy stuff? We could throw away and replace everything that's affected except the built-in pantry shelves, but that seems wasteful. Is there a better home remedy than vinegar?

Fresh Bread

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Re: Dehumidification... is that a word? It is now.
« Reply #13 on: October 09, 2018, 01:51:31 PM »
Clove oil, available from pharmacies, is supposed to help to stop mould growth. Google for the dilution ratio. With furniture do a patch test. Leaving stuff out in hot sun will help too.

wheezle

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Re: Dehumidification... is that a word? It is now.
« Reply #14 on: October 09, 2018, 02:01:13 PM »
Two posts so far talking about desiccants.

I'm fascinated by the idea of using desiccants. I currently have a little, porous bag of salt sitting in my basement that drips into the sump hole. It's like a dehumidifier that costs nothing to run.

However, I don't know how much salt I'd need to actually put a dent in the humidity issue. It's something I'll be testing with a more scientific approach, but I'm curious if anyone else has tried this to any great extent...

simonsez

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Re: Dehumidification... is that a word? It is now.
« Reply #15 on: October 09, 2018, 04:50:42 PM »
Two posts so far talking about desiccants.

I'm fascinated by the idea of using desiccants. I currently have a little, porous bag of salt sitting in my basement that drips into the sump hole. It's like a dehumidifier that costs nothing to run.

However, I don't know how much salt I'd need to actually put a dent in the humidity issue. It's something I'll be testing with a more scientific approach, but I'm curious if anyone else has tried this to any great extent...
At the family vacation home we always had those little buckets in each room in the basement as it tended to be a little damp.  It was a kid's chore to empty all the water out (to let the dessicant absorb again).  I'm not sure how big of an impact it had but there would be a half inch of water in there after a month or so.  I guess that's better than all that water being in the air potentially contributing to mold/mildew/general mustiness.

I guess you could have dessicants in one room and not in the other and see how they differ over the years but the cost isn't prohibitive to begin with.

wheezle

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Re: Dehumidification... is that a word? It is now.
« Reply #16 on: October 09, 2018, 05:09:14 PM »
I guess you could have dessicants in one room and not in the other and see how they differ over the years but the cost isn't prohibitive to begin with.
Fortunately, it would be a cheap test, yes.

I may also get myself a well-reviewed hygrometer. I feel like I'd like to have that anyway... and it'd lend some precision to this test.

(I have a vague feeling that when I run the numbers, I'll just end up with a dehumidifier, but this is too potentially neat an idea not to try it.)

jlcnuke

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Re: Dehumidification... is that a word? It is now.
« Reply #17 on: October 10, 2018, 06:16:49 AM »
Run your AC. Mold remediation and health issues will cost you a lot more in the long-run than your electric bill from using your AC system...

tralfamadorian

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Re: Dehumidification... is that a word? It is now.
« Reply #18 on: October 10, 2018, 06:36:42 AM »
No one has mentioned this yet so Iíll throw it out there. If the weather is cool and humid vs hot and humid, a fire in a wood stove or fireplace is great for pulling moisture out of the air.

Mr. Green

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Re: Dehumidification... is that a word? It is now.
« Reply #19 on: October 10, 2018, 08:58:43 AM »
Living in a high humidity area and keeping windows open all the time is not compatible. No way around that. Doesn't matter what solution you choose, it will not be effective if you continue this practice.

wheezle

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Re: Dehumidification... is that a word? It is now.
« Reply #20 on: October 10, 2018, 02:29:11 PM »
No one has mentioned this yet so Iíll throw it out there. If the weather is cool and humid vs hot and humid, a fire in a wood stove or fireplace is great for pulling moisture out of the air.
I like this thought. With autumn here, I'll be seeing plenty of cold-and-humid days.

Takk

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Re: Dehumidification... is that a word? It is now.
« Reply #21 on: October 11, 2018, 08:29:06 AM »
note: amount of water in the air at 55F and 100% Relative Humidity is equal to 75F at ~50% relative humidity (the "ideal" condition)

Cold and Humid usually isn't an issue under ~ 57F in the worst of conditions.


Fire usually draws outside air into your home (heat rises, removes air from the house, house replenishes that through cracks/holes in the structure, increasing airflow and outside air)
So if the outside is dry, this does remove moisture in your house. if the outside is wet, it does not. (dry/wet is relative, by grains per pound of dry air, if it's below 55f outside, it's most certainly dry, and usually is when one sparks a fire in the fireplace)

In short, don't set a fire in the fireplace when it's 62-65+F outside and really humid expecting it to dry the house.

I usually use http://www.sugartech.co.za/psychro/index.php for my psychometric calculations when I'm lazy. if anyone wants to play around with it to determine how to dry anything based on temperature/humidity.


historienne

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Re: Dehumidification... is that a word? It is now.
« Reply #22 on: October 11, 2018, 08:53:38 AM »
If you're getting mold, then you need to dehumidify.  Given the temperatures, it sounds like you need to use a dehumidifier.  So yes, either some more portable dehumidifiers, or a whole-house system.  If you go with portable dehumidifiers, you can try to rig them up to run continuously (by, for example, elevating the unit and having the hose drain directly to a sink).  Probably not possible everywhere, but if you can get that to work in the kitchen and bathrooms, you may find that you've solved the problem.

clarkfan1979

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Re: Dehumidification... is that a word? It is now.
« Reply #23 on: October 11, 2018, 09:22:43 PM »
Only open the windows when it's not humid outside.

When it's cool outside, run the dehumidifier. When it's warm outside, run the A/C.

When it's humid outside, run something 1 every 3 days for at least 4 hours or twice/week.

Plugra

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Re: Dehumidification... is that a word? It is now.
« Reply #24 on: October 16, 2018, 07:18:16 AM »
Running a dehumidifier is not the best option if you live in a warm climate, because the dehumidifier will release heat while it removes water from the air.  (The heat released is equal to the electrical power consumed.)  So it warms the house, unlike the A/C which at least ejects the heat to outdoors.

Dessicants reduce humidity but it would take a huge pile of dessicant to reduce the moisture in the house significantly, and then you have to find a way to recycle (dry out) that dessicant.  That consumes energy.

So unless you live in a rather cold damp place you are probably better off just running the A/C enough to dry out the house.  I live in FL and keep my A/C at 78F when home, which is more than adequate to keep the mold away.

Takk

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Re: Dehumidification... is that a word? It is now.
« Reply #25 on: October 16, 2018, 11:42:46 AM »
If you're ever looking to install an AC system for a room for dehumidification purposes, you want a system that is slightly undersized so that it runs all the time / can be variable to increase run time. This is why oversized systems in homes is actually a problem! the moisture increases in the house, but the thermostat says it's satisfied, and does not turn on the AC to remove that moisture from the air.


Dessicants are great, but for home use they are a bit of a pain. I'm still working on the regen system for a lithium chloride liquid solution to assist homes in FL. So far nothing has been super elegant.