Hot Topics: Winter Condo Humidity

window condensation

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Original Post: High humidity in condo in winter

JeremyLeib - Member

Hi everyone,

Here is our issue: We live in Chicago in a condo that's about 900 sq ft (two bedroom, two full baths). The building has five units on each floor and is three floors high. We are on the third floor and are on the NW corner of the building. The roof is a flat parapet roof.

Since moving in, we had issues with lots of condensation on the windows and with surface mold growing on the walls on the north side of our unit (usually in corners). I had just been wiping the walls frequently and spraying with anti-mold spray. Recently, though, I bough a meter for humidity and found out that the humidity in the winter in our condo is about 50-60% and even higher near the exterior walls. I had someone check out our HVAC (electric, in unit), and it does not have a humidifier in it. We have recently bought a dehumidifier (70 pint old system, 50 pint new system), and that is taking lots of water out of the air and bringing the humidity down to between 35 and 40%.

So while the dehumidifier seems to be a great help, I am still wondering how so much humidity is getting into our place when usually the issue in winter is that places are too dry. We have been here about 3 years, so I assume any water leaks in the walls or ceiling/roof would have become apparent by now. It is a brick building, so could it be a tuckpointing issue? Any advice would be appreciated!

XSleeper - Group Moderator

Brick and mortar absorb moisture out of the air no matter the season. But in the winter cold walls (north walls are the coldest) can become just like a giant dehumidifier coil. Just like a cold dehumidifier coil or a cold bathroom mirror or cold window will get condensation on it when warm moist air comes into contact with it, cold concrete is going to sweat. Since its porous, it will hold a lot of that moisture.

All you can do is keep dehumidifying... and keep your walls clean.

Marq1 - Member

We have no idea what the building structure, how it's built, or what materials!

Type in winter everything drys out so if your getting that much moisture, and your not humidifying your unit, it has to be coming from somewhere.

Showers and laundry, with cooking a distant third, are the biggest sources of moisture generated in a home.

Where are all these vented in your building?

manden - Member

Do others in the condo also have humidity problems?

If you have vents, check that they are actually working.

Pilot Dane - Group Moderator

I would make sure you are running your bathroom vent fan while bathing and let it run at least 20 minutes after you finish a shower. You can replace the switch with a timer switch if you want so you don't have to come back later and turn the fan off.

Since you are in a multi unit building the moisture may be coming from neighbors. If they are running humidifiers or taking hot, steamy showers without the vent fan then some of that moisture can be passing through the walls into your unit.

I would keep running the dehumidifiers. You probably will always have condensation on the inside of windows on cold days but you can minimize it. Keeping the relative humidity (RH) below 50% would be my goal.

I would also keep your house thermostat at a constant setting. Relative humidity changes with temperature. Your house may have a good RH when at home and have the heat set warmer but if you set the thermostat back when away the temperature will drop and the RH will rise.

Norm201 - Member

With regard to Xsleeper's comment, shouldn't the buildings vapor barriers reduce or eliminate the moisture from coming inside? If what you say is true, many buildings and brick homes would seem to have a major problem. But I've never heard of high humidity to be caused from brick structure.

JeremyLeib - Thread Starter

Thank you, all, for the replies and advice! Here are some of my follow-up comments:

- Regarding the construction, I don't know much. I know the exterior is brick and the final interior layer is drywall. I don't know what's in between.

- Regarding neighbors, previously when I didn't make the connection that the mold was connected to high humidity, I did ask three of my neighbors if they got surface mold on their outer walls. No one really did. The person right below us had a small patch of mold on the corner between the wall and ceiling in one of her rooms. I just yesterday gave my hygrometer to the neighbor across the hall (SW corner of the building) to see what they measure. I haven't heard back yet. He did say, though, that he definitely feels the difference here compared to other places he's lived that there is no need to have humidifiers here.

- Regarding sources of humidity, we don't have an in-unit dryer. There are vents in the bathrooms and kitchen that seem to work. It's true that we don't often turn on the fans, but it would still seem strange to me that in winter with people mainly dealing with low humidity, I would have so high humidity just because I don't use the bathroom fan. Likewise if the humidity is coming from the neighbors: can there really be so much? We don't share a wall with any neighbors since there are hallways on the other sides of our walls, so it's just the neighbor downstairs that we directly border.

To give an update on the dehumidifier, the first couple days after buying it, it was on pretty much all the time, it brought the humidity down to between 35 and 40%, and it filled up (1.5 gallons) twice a day. Now a couple days more later, it seems to fill up a bit slower. Is that what I should expect? Should it pull a lot out of the air at first, and then we hit a time when it's able to pull water out of the air faster than water is entering the air (from whatever source)?

I'll add also that the manager of the HOA did say a year ago at the homeowners' meeting that some tuck-pointing people had said that our building needs exterior work done. I don't remember the terms, but it was like tuck-pointing but more than that. The blocks under window had shifted and were not straight and other issues like that. We are still working out whether that work will be done with us needing to pay a special assessment. Could that be contributing?

Thanks again for any thoughts. If we have to just always run a dehumidifier in the winter, I guess that's not the worst thing. It just does cause some noise, and it would settle my mind if I knew where all the moisture is coming from.

XSleeper - Group Moderator

Window sills that are in a state of disrepair can be a big source of moisture in a wall. Water runs down the building... hits the sill... goes in the cracks under the windows and on the ends of the sill... gets trapped behind the brick. That water has to dry out... so it migrates both directions... some of that moisture ends up inside.

Yes, humidifiers act like that. You can also lower humidity in the winter by cracking a window open slightly to let some dry air in. Whatever is most comfortable for you to do. The best humidifiers will run constantly and dont need to be emptied... they have a bulge pump and drain hose that can go directly into a drain.

manden - Member

People dealing with low humidity is usually people with older furnaces.

They use interior air for combustion so pulled in dryer outside air to replace this.

You have electrical so there is nothing drawing in low humidity air.

Use your bathroom fans when showering etc,

Use the stove hood if you have one and it vents outside especially when boiling water.

Also every time you exhale you exhale moisture.

GregH - Super Moderator

Your high humidity problem has very little to do with the building's construction and more to do with a lack of air change.

You would need to first see if there are any exhaust ducts from the building's air system that would do this.

Older apartments may not have anything for this. At one time leaky windows would take care of air change but energy effiecy window ugrades seldom take this into account.

Depending on how much moisture you add to the air and with poor construction you could need between 50 and 100 cfm of continuous air change.

Presumeably you have a bathroom exhaust fan and running it continuously for a week or so would tell you if it would help you.

Keep in mind that modern construction homes have an air exchanger running 24\7 and with more airchange than what I suggested you try.

JeremyLeib - Thread Starter

Thank you all for your posts. One small point of new info: I gave my hygrometer to the neighbor across the hall. They have one more person in the same size apartment as we do. He said that the meter showed around 42% at various areas in the unit, so they don't have the same problem. Regardless, it sounds like the issue isn't something we can deal with apart from a dehumidifier.

It's either structural, or it's an air exchange issue (and I don't think we are going to start running all fans and exhaust vents 24/7). The dehumidifier is working great, but it's just the minor inconvenience of the noise of the fan. BTW, the model we got seems to run the fan continuously. I can hear the times when the actual dehumidifying action turns on and off, but the fan is just on all the time except for short breaks of about 30 seconds here and there. Are most dehumidifiers like that? Thanks!

Marq1 - Member

Not that I have seen, the ones we had/have simply cycle on/off as needed!

Norm201 - Member

I've heard people complain about this same problem. Not sure why. I have not had experience with newer dehumidifiers. My 1978 White-Westinghouse keeps chugging along even when it's encrusted with ice because I forget to turn it off. They don't make them like they use to.

JeremyLeib - Thread Starter

Thanks for the replies about the dehumidifiers. Actually doing a Google search (which I suppose I should have done before asking here anyway - sorry), I found out that different brands (and even different models from the same brand) are designed to either shut the fan off when the compressor isn't working or to leave the fan on all the time. There are then, not surprisingly for the internet, lots of arguments about which is better.

Pilot Dane - Group Moderator

I've had a bad experience with one dehumidifier. It had electronic controls and every time the power blinked it lost all it's setting and you had to go back and turn it on and configure it the way you want. It's not as big a deal if it will be out in the open where you see it regularly but it can be very annoying if the dehumidifier is used in a basement or storage room you don't visit regularly.

Also consider if you want to manually dump the catch bucket. If you are able to connect a hose and have it drain via gravity. Or, get a model that has a pump so the water can be pumped up and out wherever you want.

JeremyLeib - Thread Starter

Thanks for the things to think about, but we've already actually bought a dehumidifier. It's a Midea which I guess isn't considered a great brand. but we're happy with it. It does what it should, and it's not loud. We have it out in the middle of our unit, so a gravity drain doesn't really help us since there aren't any drains in our living room floor.

I suppose if we had bought one with a pump, we could have put it in a bathroom or kitchen, but having it in a more central location in the unit seems better. While the fan isn't excessively loud, the constant fan still adds noise to our home. Reading some articles online about why it's better to have a dehumidifier with a constant fan, though, has made me less annoyed by it. Thanks again!