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Discussion in 'HVAC' started by Billbill84, Dec 5, 2019.
Here's how it's set up
So here is a problem I'm having with this issue right now. We bought this place 4 years ago. I inspected everything and the place was solid, no serious issues. We installed hardwood floors and my wife has serious sinus problems so I installed a whole house humidifier. We keep the RH about 40%. Last winter after a long really cold spell I noticed dripping from an odd place, like the roof was leaking. I crawl in the attic and it's raining in there, sopping wet mold everywhere. I panic but discover the 2 bathroom vents just vent to the attic space. Well I correct that with proper though the roof vents and think I'm good, it'll dry in the summer heat. Well I crawled up there 2 days ago now that's cold again to make sure it's still dry and to evaluate the mold and decide if I need to look at remediation. Well it's better but I still have too much moisture. I can see a drop of water on the ends of many nails. So the only thing I can think that is different since we moved in is the humidifier. So I'm back to the drawing board to figure out what to do.
You have attic rain. 40%RH during a cold spell is way too high I think
When I research proper indoor humidity for health and comfort it almost always suggest 3 5-50%.
Yes depending on the outside temperature!
You should be able to find the manual online, to explain the operation.
You have to lower the humidity setting as the temperature goes down, or you will get the condensation problems you have now.
You can also install a roof ventilator fan, which can work year round.
It pulls out hot air in summer, and in winter it comes on when the air gets too clammy and pulls that out.
You also might need to improve the air circulation and intake-exhaust venting openings.
Soffit vents can also get blocked by insulation.
As far as the mold, you can use Concrobium mold killer from Home Depot or elsewhere.
You can rent a Concrobium fogger, which fogs all the wood surfaces.
The Concrobium kills the mold and encapsulates it as it dries.
It needs to be done when the wood is dry, like in warmer weather.
I saw your table of indoor RH vs outdoor temp. I found that same thing online in 1 place. So what does the outside temperature have to do with the indoor RH? The indoor RH is controlled to keep wood from drying out, to keep the house more comfortable, for health reasons, such as preventing sore throats, dry sinuses, etc, reduced static charges, and many other things. That's the whole point of humidifing a house. The numbers you posted would be about what the RH would be at those Temps is you didn't add moisture to the air. So I don't understand the correlation of the outdoor temp and indoor RH, can you explain the logic to me?
Because most houses have some problems with cold spots, air leaks, voids in insulation, drafty windows, or poor ventilation in the attic or crawlspace, the humidifier can add too much moisture than the house can tolerate, as the temperature goes down.
So even though it seems counter-intuitive, you usually have to back off the humidifier output as the outside temps drop.
Even though you would actually want that extra moisture, you have to make a sacrifice and cut it back, or else you will usually get a condensation problem, which gets worse as the outside cold affects surfaces in the house or attic.
Oh I undeserved that but if everything is properly designed and functioning then there is no issue. If you think 15% RH in your house is ever good I whole heartedly disagree.
As I wrote in an earlier post here, the humidifier that I installed last winter came with an outside temp probe that is tied into the controller and reduces RH in the house as the temp drops outside. Since I assume the engineers who designed the thing probably are a lot smarter than I am about how the RH in the home should work, I would say that table is pretty close to correct. I don't have the table that was enclosed with the humidifier.
"2 bathroom vents just vent to the attic space."
That's a NO-NO!
Bathroom vents should be ducted to the exterior.
That's only when the outdoor temperature is lower than 20-below.
I believe it has to do with the dew point, which, of course is the actual point where you start getting damaging condensation.
If it is too dry for you, you can increase it a bit but should then try to insulate your house better.
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