Replies

1. 
   Jon_R | Jan 21, 2019 02:03pm | #1

   > a whole house humidifier in the winter.

   What happens to attic humidity when you don't run the humidifier?

   > no good way to circulate air between this space and the remainder of the house

   But some conditioned air is what it needs.

1. 
   lakee911 | Jan 21, 2019 02:32pm | #2

   Jon,

   Thanks for the reply.

   The humidity goes up. I has been slowly increasing the dehumidier humidity level setpoint until the space got to a point where I feel it's not too too high. In the summer it was like a sauna without it running. I've not had the dehumidifier completely off in the winter to know what it would naturally be, but I have had a lot of condensation on some of the double pane windows as it is already.

   Where does one get "conditioned air" in the winter?

   Thx?
   Jason

2. 
   charlie_sullivan | Jan 21, 2019 03:07pm | #3

   You might find this article helpful.

   https://www.greenbuildingadvisor.com/article/measuring-and-understanding-humidity

   If you get a hygrometer that displays the result in terms of dew point (e.g. ones suggested there), or use an app to convert temperature and humidity to dew point, you'll see that, in the winter, most likely, the air in the attic has about the same dew point as air in the house, and the relative humidity is higher because of the cooler temperature. You can opt to allow that situation to exist (70% humidity in cold temperatures is not going to cause any problems), but likely you have some air leaks that you could seal and get other benefits as well.

   Air leaks in the lower portions of the house (e.g., the basement) allow outside, dry air to get in. You then humidify that air, and the hot air rises, finding miscellaneous ways to get into the attic, and then leaks out other leakage paths from the attic to the outdoors.

   If you found and sealed those leaks, you would have much less cool air coming in, so you'd have much less need for a humidifier. Even much further north, people who think they need humidifiers likely actually need air leaks sealed. A house that is well air sealed will tend to stabilize at a reasonable wintertime humidity level. You would save energy on running the humidifier and on running the heat. You'd have less air going up to the attic. Then you'd have a few options for how to reduce the humidity there, although you could also accept that it will be fairly high humidity and be OK it.

   1. You could still run the dehumidifier, but it would have to run much less. With less air leakage, it would dry out the air and the materials up there, and then it would be done running much--it would just have to run a little to overcome the leakage.

   2. You could aim for a lower humidity in the main house. You would probably have high enough humidity for comfort without ever running the humidifier.

   In the summer, the problem is humid outside air leaking into the attic. The air sealing you do for winter will also help that problem. You probably will want dehumidification in the summer--high temperatures plus humidity are worse for mold, etc. growth than are low temperatures plus humidity. You can do that with a dehumidifier or with air conditioning. Doing it with air conditioning is advantageous because it will reduce, rather than increase, the heat that comes down from the attic into the other areas you are cooling.

1. 
   lakee911 | Feb 27, 2019 10:53am | #6

   Thanks for the article, Charlie. I've been reading up on dew point and relative humidity and I think I've almost gotten my head wrapped around the concept. I'm having a bit of trouble sometimes, though, making sense of the numbers.

   I placed my Netatmo weather station in the attic and I've been logging data for a few weeks. Currently, it's 56.3 deg F w/ 60% relative humidity. I am still running the dehumidifier so I'm limited to about 60%. That makes the dew point about 42 degrees.

   According to my Nest thermostat in the main house (located in the living room, two floors lower than the attic), the temperature is 71 degrees with 37% relative humidity. That makes the dew point 43 degrees!

   So, if I understand this correctly, the attic is actually slightly dryer than the house. Right? My next step is going to turn the dehumidifier off and see what happens...

3. 
   walta100 | Jan 21, 2019 06:10pm | #4

   Sounds to me like you did half the job of creating a conditioned attic.

   You have sealed and insulated it, now you need to condition the attic by adding supply and return registers in the attic. When done correctly the attic will have almost the same temp and humidity as the rest of the house.

   Walta

1. 
   lakee911 | Feb 27, 2019 10:55am | #7

   Walta, you are correct. At some point in the future, it will be conditioned. Having the same temp and humidity is certainly the goal.

4. 
   Peter Yost | Jan 23, 2019 11:09am | #5

   Hi Jason -

   It is important for us to confirm how you are measuring your interior temperature and relative humidity because it is notoriously difficult to accurately (and inexpensively) measure humidity.

   If indeed your attic humidity is running at that high of levels, next we identify the source(s) of that moisture. I am not quite sure why you would run a humidifier in the winter at the same time you run a dehumidifier. When you turn your wintertime humidification system off, what sort of humidity level/content do you have in your attic?

   Also, what type of humidification system do you have?

   Was your insulation/airsealing of the attic guided by a BPI-certified audit, including a blower door test? It's hard to understand home performance without complete info on both heat and moisture flows/transfers in your home.

   Peter

1. 
   lakee911 | Feb 27, 2019 11:10am | #8

   Hi Peter.

   I had a very inexpensive temperature/humidity thermometer in the attic for a long time. I did move my Netatmo weather station into the attic, though. It can log data. Please see reply to Charlie, above, for instantaneous data points. The dehumidifier up there is still on, but I am going to turn it off tonight.

   I'm hoping that my (previous?) misunderstanding of relative humidity is the issue here. I can turn off the humidifier, though, and see what difference that makes.

   The humidifier in the house, which is located in/on the basement air handler, is the type where water drips through a media pad and warm air blows through it from the supply into the return. That air handler serves the basement, first floor, and second floor. The attic is above the second floor.

   Regarding the BPI-certified audit, no it was not. Although I have had a blower door test done before, I was told by my last energy auditor (many years ago and many projects ago) that I shouldn't do one (and they wouldn't do one) because I do have vermiculite insulation in my house. Wouldn't want to potentially blow around potentially-asbestos-laden insulation around the house.

   I am working to seal air leaks in the remainder of the house. Unfortunately, though, most of my windows are from the 1920s. I have storms, but they're a bit leaky. Some maintenance is in order... Anyhow, I'll turn the dehumidifier off in the attic tonight and I'll turn the humidifier in the house off next week and see what happens. Wife generally complains that it's too dry when the humidifier is off....

   Thanks,
   Jason

5. 
   lakee911 | Mar 13, 2019 07:55pm | #9

   While it was cooler outside, the dew point in the attic and house matched. Now that it has warmed up some, they're off. So far it's six to eight degrees higher in the attic than the house!

   What does this mean and is it okay?