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Old 01-14-2010, 12:14 PM   #1
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humidity question


i have a furnace with an auto humidifier on it that i can actually control a little bit, we are drying out in our house, can we just crank that thing up or are we going to run into some moisture problems that I don't know about? thanks!

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Old 01-14-2010, 12:36 PM   #2
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If it's comfortable, then you probably won't have problems. If you get a hygrometer you can measure the relative humidity. Mold can grow if it's over 80%, but it has to stay there for a while.

If you can generate static electricity when you walk across a carpet, then you're probably 40% or lower.

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Old 01-14-2010, 12:50 PM   #3
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excellent, thank you. my elbows and kids skin thank you also
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Old 01-14-2010, 02:34 PM   #4
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Actually. Mold can grow if your indoor humidity is over 50%. usually doesn't happen until it goes over 55% though.

What humidifier do you have. Does it have a control that provides freeze/frost protection.
Do you have single pane windows.

What is your indoor humidity, and your outdoor temp.
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Old 01-14-2010, 02:57 PM   #5
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HUD, the EPA and Mold Help.org and almost all others state that humidity should be maintained in a house at no higher than 50%. This is the only way to control mold growth outside of removing any organic materials in the home.
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Old 01-14-2010, 03:14 PM   #6
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Originally Posted by Bob Mariani View Post
This is the only way to control mold growth outside of removing any organic materials in the home.

Which would include removing people from the home also.
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Old 01-14-2010, 09:03 PM   #7
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Originally Posted by beenthere View Post
Actually. Mold can grow if your indoor humidity is over 50%. usually doesn't happen until it goes over 55% though.
The EPA has a different opinion (not saying you're necessarily wrong, but they say differently).

According to my cheap hygrometer, my house has been sitting at 60% RH for 10 years with no mold growing. I tend to think my hygrometer might be fairly accurate based on the relative feel between the office and home.

According to weatherunderground.com, my average humidity for this date for the last 5 years has been around 70% -- and the winters are dry.
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Old 01-14-2010, 09:30 PM   #8
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Are you reading the ratings for air/middle of the room humidity. Or for surface humidity.
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Old 01-15-2010, 09:10 AM   #9
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In the past I have lived in Miami, and Myrtle Beach and I have never seen mold grow on anything that hasn't at least occasionally been wet. Now they may better survive till the mold is again wet with high humidity, but I suspect very few mold species actually have any significant growth. That they do seems to come from the A/C and dehumidifier industry. There are similar unrealistic claims that nobody wants to counter in the fire hood industry. IMO more to do with law suits than real fact.
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Old 01-15-2010, 09:11 AM   #10
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Originally Posted by pyper View Post
The EPA has a different opinion (not saying you're necessarily wrong, but they say differently).

According to my cheap hygrometer, my house has been sitting at 60% RH for 10 years with no mold growing. I tend to think my hygrometer might be fairly accurate based on the relative feel between the office and home.

According to weatherunderground.com, my average humidity for this date for the last 5 years has been around 70% -- and the winters are dry.
Do you have a link to that information? We have people fighting outside economizers based on what IMO is false.
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Old 01-15-2010, 09:14 AM   #11
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Quote:
Originally Posted by Bob Mariani View Post
HUD, the EPA and Mold Help.org and almost all others state that humidity should be maintained in a house at no higher than 50%. This is the only way to control mold growth outside of removing any organic materials in the home.

I doubt that. ASHRAE still says houses should be maintained between 40 and 60%. If it were true I would think they would lower that standard. And we would have to but larger AC's, possibly with reheat.
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Old 01-15-2010, 11:58 AM   #12
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Quote:
Originally Posted by beenthere View Post
Are you reading the ratings for air/middle of the room humidity. Or for surface humidity.
Air

Quote:
Originally Posted by H. Phillips View Post
Do you have a link to that information? We have people fighting outside economizers based on what IMO is false.
The weather or the other?

Assuming the other: "The vast majority of mold species require "water activity" levels that are equivalent to material equilibrium moisture contents corresponding to relative humidities of at least 70%. In fact, the great majority of serious, large mold outbreaks inside buildings occur where porous, cellulose-type materials have literally been kept wet by liquid water or sustained condensation." [emphasis added]

http://www.fsec.ucf.edu/en/consumer/...moldgrowth.htm

What's an "outside economizer"?

Quote:
Originally Posted by H. Phillips View Post
I doubt that. ASHRAE still says houses should be maintained between 40 and 60%. If it were true I would think they would lower that standard. And we would have to but larger AC's, possibly with reheat.
EPA currently recommends "below 60%"
http://www.epa.gov/mold/moldcourse/index.html << see chapter 9
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Old 01-15-2010, 12:42 PM   #13
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What's an "outside economizer"?
That should have been "outside air economizer". In large buildings, not houses it is common to bring in up to 100% outside air instead of room return air when the outside temperature and humidity is below the room air temp and humidity. Actually now they use a digital computer to calculate the enthalpy or total heat of the outside air and compare that to the indoor air, if the outside air has lower heat than the inside air then they use the outdoor air instead of the indoor air. The outside air could be of a higher temp of the indoor air but if it has very low humidity it could take less energy to cool it instead of the indoor air. The fear is that when they malfunction they could bring in outside air when they shouldn't and the room humidity may be too high. We usually use outside temp limits to prevent that. Some places don't maintain them well but when they do they work very well.
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Old 01-15-2010, 03:22 PM   #14
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As you see, it says great majority. Not all.

Next. Its surface humidity( the part about material humidity in that article ) that will determine mold growth more then air humidity.

In winter time.
You can have 70F temp 60% humidity at a wall in a hallway in your house. And 71%RH at the inside corner of a outside wall. And condensate running down a window when its 50F outside. Creating higher humidity/water activity levels.

If you have 70F temp and 50% humidity at that same hallway. That same corner that had 71% humidity will no be less then 60%.

By keeping your air humidity to 50% and less. You help to prevent material humidity levels from becoming high enough to support mold growth.
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Old 01-15-2010, 03:42 PM   #15
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Originally Posted by beenthere View Post


By keeping your air humidity to 50% and less. You help to prevent material humidity levels from becoming high enough to support mold growth.
No argument there, although that would require running the AC 12 months of the year.

Just as an isolated data point: I get condensation on the drywall over my shower every single day of the year. It's on an outside corner, so it's a lot more condensation in the winter. It's just plain old drywall. Every once in a while it gets a little mould growing on the paint, so I wipe it off. It's been like this for about 10 years now. I've recently had the opportunity to inspect the other side of the drywall, and there doesn't seem to be a problem.

Maybe in time there will be, but I think there are probably a lot more important issues to worry about.

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