condensation opinions


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Old 12-08-11, 10:29 AM
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condensation opinions

I have been batteling high humidity and its repercussions.

I have a sante fe dehumidifier in the basement which works well in the summer. In the winter the main floor of the house becomes the problem w a RH of 60+.

I recently had a blower door test done and they said the house is too tight which i found surprising in a 1960 house w orig windows/doors.

A HRV is not in the financial pic right now. so the question is should I use exhaust fans, which will inc heating bill or put floor ducts in and hook up the dehumidifier to the house during the winter?

I am in ny, the house is a ranch w oil boiler and baseboard
 

Last edited by lupi2279; 12-08-11 at 10:59 AM.
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Old 12-08-11, 11:40 AM
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Hi lupi, I don't recall NY being all that humid.

First thing that comes to mind is the dehumidifier, In colder temperatures the inexpensive ones don't work as well. If you are monitoring its output, then you should have some idea.

Outside air at this time of year will typically be dry as a bone once brought into the house and heated. Some extra fresh air will definitely lower the rh.

The usual items need to be checked, dryer vented to outside, not drying laundry in house, running bath exhaust fans for 20 minutes after showers. Bath fans also exhausted to outside.

Does the basement or crawl have a dirt of concrete floor and any water down there?

If dirt, that's your source of moisture.

That will get us started.
Bud
 
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Old 12-08-11, 11:55 AM
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First thing that comes to mind is the dehumidifier, In colder temperatures the inexpensive ones don't work as well. If you are monitoring its output, then you should have some idea.


Santa Fe Classic Dehumidifier this is the dehumid. It works well even in winter although im surev its eff drops considerably

The usual items need to be checked, dryer vented to outside, not drying laundry in house, running bath exhaust fans for 20 minutes after showers. Bath fans also exhausted to outside.

all is ok and being done on this front. Im thinking of hooking the exhaust to a dehumidistat

Does the basement or crawl have a dirt of concrete floor and any water down there?

no, but i suspect there is no vapor barrier. hence the dehumidifier in the basement (which can be ducted to a remote location, w a $100 kit)
 

Last edited by lupi2279; 12-08-11 at 12:29 PM.
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Old 12-08-11, 01:42 PM
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Most sounds ok, but you lost me on the dehumidistat and ducting the output of the dehumidifier to another location.

Although moisture can move through the concrete floor and walls, it does so rather slowly. Anywhere you are getting a lot of moisture will often show a white chalky residue, called efflorescence.

Do you recall the number they got when they said the house was too tight. It could have been in CFM with the blower door test, CFM50 number, or it could have been converted to ACH. Were they an audit only company or were they interested in selling you their services and that HRV.

You mention condensation, where is it being a problem, all over the house, or one area vs another.

Try this RH calculator and take some reading around the house to see if one area has more moisture than another. In a typical home in the winter, air flows in through leaks into the lower portions, including the basement, and then moves up and out the upper portions. All of the air in your home is exchanged every 2 to 3 hours, so with no added moisture, the inside humidity should quickly stabilize at the temperature corrected number you would get from the outside air. Are you closer to Queens or Buffalo?

Bud
 
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Old 12-08-11, 01:54 PM
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but you lost me on the dehumidistat and ducting the output of the dehumidifier to another location.

I can duct the dehumidifier input and output to the upstairs in the winter.

or

I was thinking of connecting the bath exhaust fan to a dehumidistat.

Do you recall the number they got when they said the house was too tight. It could have been in CFM with the blower door test, CFM50 number, or it could have been converted to ACH. Were they an audit only company or were they interested in selling you their services and that HRV.

Ill get the #. The company recomended some insulation w no additional air sealing. they did not recommend a hrv. they recommended running bath fan on a timer throughout the day.

You mention condensation, where is it being a problem, all over the house, or one area vs another.

all over. windows are like we have a greenhouse in the am. need to monitor corners of ceiling for mold, toilet sweats.
 

Last edited by lupi2279; 12-08-11 at 03:22 PM.
  #6  
Old 12-08-11, 02:24 PM
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Originally Posted by lupi2279 View Post
I was thinking of connecting the bath exhaust fan to a dehumidistat.
Why? Is the bathroom exhaust fan vented inside?
 
  #7  
Old 12-08-11, 03:19 PM
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no. to draw in cold dry air. and bring the winter humidity down to a max predetermaned #


Blower door results:
Target cmf50
bas 1454
CFM 50 building leakage 1945
fan ring A
house pressure -0.3
fan pressure 50
 
  #8  
Old 12-08-11, 04:36 PM
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What is the sq footage?
What is the RH and temp in the basement.
Any sump pump in operation?
Where does the dehumidifier drain?
Since the problem continues into the winter, and that is when the baseboard heat is kicking in, there is the possibility of a leak somewhere.

Now, take your basement temp and RH and use this calculator link I forgot to give you and calculate a dew point for down there. Then use that dew point and your upstairs temp to see what the basement air RH would be as it moves up into your living space. If the RH is lower than what you have on the main floor, then your source of moisture is upstairs. If the RH number is higher than what you are seeing upstairs, then the basement is contributing to the upstairs RH. A little wordy, but it is part of the process to narrow down the source of that moisture.

Temperature, Dewpoint, and Relative Humidity Calculator

Bud
 
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Old 12-09-11, 06:00 AM
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What is the sq footage?

1500

[B]What is the RH and temp in the basement.[B]

I keep the RH about 45. this time of year temp is about 50

Any sump pump in operation?

no

Where does the dehumidifier drain?

pumps int a sink


Since the problem continues into the winter, and that is when the baseboard heat is kicking in, there is the possibility of a leak somewhere.

i cant see how, it would be apparent

take your basement temp and RH and use this calculator

w/o the dehumid running? or just however we normally have it?
 
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Old 12-09-11, 06:05 AM
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I will say that although we always have battled humidity. This year is worse I believe because I my daughters are teens and taking longer showers, even though i think we are pretty diligent on using the exaust fan on 20 min timer
 
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Old 12-09-11, 06:50 AM
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If your house is overly tight, the showers could be part of the problem - humans contribute a lot of moisture to a building when they go about their daily activities.
 
  #12  
Old 12-09-11, 07:40 AM
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First, when the air in the basement is 50 degrees and an RH of 45, it is dry. Using the calculator, 50� with a of RH = 45% yields a dew point of 29.5�. Using that dew point, which represents your moisture content, and 70 degrees once that air migrates upstairs, you end up with a RH = 22%. So basement air moving upstairs is helping to hold the total RH down.

Your CFM50 isn't ultra tight, but given your current humidity battle I would agree to not making it tighter. You are currently running at one complete air exchange every 2 hours. However, you are heating with baseboard hot water, which has no air circulation system. If your moisture source is not in the path of incoming and exiting air, then you could be experiencing the effects of a much tighter home. Example. If, in the area of your home farthest from the moisture source, lets assume the bathrooms for now, you have the lions share of that in and out leakage. Then you house may be experiencing one air change every 2 hours, but the moisture zone may only be seeing one change every 6 hours, ultra tight.

When your bath exhaust fans are running, where is the replacement air coming from, under the door? If the incoming air is limited, then so is the outgoing, even though the fan is running.

If you have a separate humidistat, move it around the house to see if the RH varies.

Please remember, I'm a long ways away and hitting on the cause here may just be luck. I'll keep guessing.

Bud
 
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Old 12-09-11, 07:40 AM
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on a slightly diff note. Can anyone explain what the blower door results mean?
 
  #14  
Old 12-09-11, 08:01 AM
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A CFM50 test is typically set up to depressurize the home to -50 pascals. If you used a water level, that pressure would be 1/4" difference between the high and low water levels, so rather low pressure. It is supposed to simulate a 20 mph wind from all directions.

The bas (Building Airflow Standard) is a target number calculated for the leakage at 50 pascals base upon the size of the home and number of occupants. More people need more fresh air. Your number came in slightly above that target, so slightly leaky, but not too bad. Bad would have been 2,500 or higher.

A ring is just the fan configuration. Not sure what the house pressure is except perhaps a water column reading, that's about 50 pascals.

To put pascals in perspective, atmospheric pressure is 14.7 psi. Converted to Pascals, that's 101,325 pa.

The 1945 is cubic feet per minute of air exiting the blower door and being replaced through the house due to the resulting -50 pa pressure.

Hope that helps.

Bud
 
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Old 12-12-11, 06:47 AM
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I have another question. As i have said the humidity is worse now but has always been an issue.


once upon a time it showed only as frost on anything metal in the attic. So when i re did the roof I added a soffit/ridge because before the attic had very little ventilation. I still get the frost issues despite this and countless hours sealing any perceivable leakage into the attic (yes fans vent outside). but i THINK it was around this time that I started getting some spots of mold in corners and certain spots on the edges of the ceilings. Is it possible that by opening the soffits I created a wind wash effect cooling the edges of the ceiling? This just hit me, Im thinking baffles w insulation packed tight to them may help if this is the case. suggestions?
 
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Old 12-12-11, 08:03 AM
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Wind washing is an issue. When I do an infrared inspection, the top of all exterior walls show cold, the wood and lack of insulation. Soffit venting can make that worse, so they make specific baffles to block wind washing. Although most any thing will work.

As for the frost on the nails, that is telling you your search is not over. If you are certain your ridge vent is open, sometimes they forget to cut back the underlayment, and the soffits are open, then there should be no frost, unless there is a lot of moist air moving up.

Now, I could probably spot it in a minute with an IR camera, but it is there and must be found. Since I know you have been working on this, many of the things to look for have already been done. However, when a solution evades you, sometimes you have to start over to be sure you didn't miss something. Here are some to look for.
1. Bath fans vented through soffits being pulled back into the attic.
2. Recessed lights leaking air
3. Tops of all walls below the attic floor, drywall to wood and holes.
4. Vent stacks passing through the attic
5. Dormers and kneewalls
6. Total vent area. 1,500 sq ft = 2.5 sq ft high and 2.5 sq ft low. If using perforated venting, you need to calculate its net free area. Pop in vents with a grill and a bug screen may deliver only 20% of the area for air movement. These numbers are for a well sealed ceiling with a good vapor barrier. Otherwise, double the area.

Bud
http://www.efficiencyvermont.com/ste...ide_062507.pdf
 
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Old 12-12-11, 03:08 PM
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I have a some of these that i have yet to install. Shop DUROVENT 22" x 4' Extruded Foam Rafter Vent at Lowes.com but now I see they sell some w a baffle. Can I use the ones I have? If so what should i use to block the wind washing? does my idea of just stuffing insulation against the baffle fly?
 
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Old 12-12-11, 03:31 PM
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You can block the air flow with just about anything. If you use insulation, just avoid fiberglass as it is designed to allow some air move through. Blown in cellulose reaches a density called dense pack, but it would be difficult to hand pack to that uniformity. The part that you probably can't do is get enough insulation over the top of the wall. Most framing just doesn't provide enough space. If you were ever to reside your home, that's when you could cover the entire exterior with a couple of inches of rigid foam and extend it up to the top of that top plate inside those soffits. Just not something you do unless the bigger project was already planned.

Back to your question, any ay you can as long as the incoming air doesn't blow on the end of the insulation and the baffle keeps a path open for cold air to get up between the insulation and the bottom of the roof.

Bud
 
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Old 12-12-11, 06:56 PM
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I will say I did not read other post so this might have been covered. First unplug that dehumidifier they are for use in spring summer and fall. 2nd condensation in heating mode is always a sign of low ventilation. Open a window a half inch and turn on a bath fan a day or two to lower rh fast. Then u might be able to back down to just a crack.
 
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Old 12-15-11, 06:06 AM
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I havent done much yet except nag family to run the bath fan.

but I got a new calibrated hygrometer and took some readings.

so FYI

Outdoor temp 54 RH-70 (a luittle warm and humid today)
basement temp 58 rh-64 (no dehumidifier running)
Inside temp 66 rh- 75 in kitchen
rh-80 in bedrooms (other side of house)

house is 1500sf ranch. bath and beds on one side kitch/LR on other end.
 

Last edited by lupi2279; 12-15-11 at 06:55 AM.
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Old 12-15-11, 07:59 AM
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I ran those numbers through the calculator to get the dew point for each. Your moisture is not coming from the basement. Bed/bath end of house is highest, thus I would question the effectiveness of your bath fan/s. If the bath door is closed during operation, there needs to be a way for fresh air to get in, or else very little is getting out.

Where does the bath fan currently exhaust?
Can you increase the run time after showers and is that built into the switch (they have them) or are you relying on the human element?

RH of 75 and 80 is extreme and needs to come down. Airman's suggestion will bring those down, especially when it is cold outside. Then you can keep monitoring the inside to see how fast the numbers come back up. Play detective with that meter and you will narrow down the location of the moisture source.

Bud
 
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Old 12-15-11, 08:05 AM
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Where does the bath fan currently exhaust?
Can you increase the run time after showers and is that built into the switch (they have them) or are you relying on the human element?


outside gable side of house. you can feel the suction when on around the door and prevents bath fogging whhen used. It has a timer set to 20 min. of course the teens like it steamy when they come out of the shower so using it properly is a constant fight.

tis has me tinking I should change the existing fan to a quieter inline fan w an automatic humidity controle
 
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Old 12-15-11, 08:21 AM
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Are the fans wired separately? If so, you could change that so they always come on when the light is turned on - that should solve your teen compliance issue.
 
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Old 12-15-11, 08:35 AM
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thanks for your help everyone
 
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Old 12-19-11, 06:19 AM
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I ran the fan 8+ hours yesteday kitch/lr rh dropped to 45-50, bath side of house dropped to the low 60s. condensation prob improved mostly on kitch side of house. gitting the br/bath side of the house below 60 seemed tough. once it got to about 60 it stayed there 4 hours despite fan and window cracked on other end of house, and it was cold out. I guess this will take longer than at least I thought.
 
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Old 12-19-11, 07:36 AM
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Remember, if you have a window open the temp may be a bit lower, thus the RH will need correcting to one reference temperature. Use that calculator and enter temp and RH reading. It will calculate the dew point. Then enter that dew point at say 70 degrees and it will tell you what the RH would be at that reference temp. If you convert all of your readings to one temperature, then you will know which ones are high and which are low. Of course your readings may have been at the same temp, but my fingers needed the exercise anyway .

Bud
 
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Old 12-19-11, 08:14 AM
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kit temp was 66
br seems to run about 3 deg cooler
 
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Old 01-06-12, 08:28 AM
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I installed a broan dehumidistat instead of the switch. what a difference.
 
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Old 01-06-12, 09:27 AM
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So now the bath fan runs based upon the himidistat setting instead of a timer or just the switch. Not sure what you have.

Bud
 
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Old 01-16-12, 02:28 PM
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So now the bath fan runs based upon the himidistat setting >>> yes


Product Detail
 
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Old 01-22-12, 01:20 PM
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you can feel the suction when on around the door
I know this thread is getting a bit old, but if you're still having trouble ... How big is the gap under the door? Our bathroom had horrendous moisture issues until I shaved 1/4" off the bottom of the door. Now more air can get in, allowing the vent fan to work much better. There's very noticeably less moisture during a shower and the fan needs less time to dry out the bathroom afterwards.
 
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Old 02-11-12, 07:47 AM
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I recently had a blower door test done and they said the house is too tight which i found surprising in a 1960 house w orig windows/doors.
Keep a couple windows slightly ajar on opposite sides of the house. No elaborate venting needed except to make sure that bathroom and all heating units are vented. The cure for an overtight house is to LOOSEN it up a bit.

Remember, you cannot take air OUT of a house without allowing an equal amount IN. Alas in Winter the IN is cold air unless you have a heat recovery systmen which you don't want for understandable reasons.
But if a house is hermetically sealed, even the most powerful exhaust fan will not remove a cubic inch of stale moist air.

I don't understand the new quasi standards which seal a house like a tomb. It used to be that a certain number of air changes was needed per hour for health reasons and I doubt human physiology has changed much in 50 years. Some modern homes seem so welded shut that one might fart in December and smell it in January.
 

Last edited by zip2play; 02-11-12 at 08:18 AM.
 

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