Blog Update!
For those of you not following me on Facebook, as of the Summer of 2019 I've moved to Central WA, to a tiny mountain town of less than 1,000 people.

I will be covering my exploits here in the Cascades, as I try to further reduce my impact on the environment. With the same attitude, just at a higher altitude!

Wednesday, October 26, 2011

Cold indoor temperatures and condensation

One of the big issues with keeping your indoor air temperatures lower (besides feeling cold) is that, for many areas, you can have a problem with moisture, condensation and mold. Not to mention that high levels of humidity will make you feel colder than the same temperature at lower levels of humidity (the inverse is true at super low levels of humidity).

Let me 'splain. Most people are comfy at around 25% - 40% humidity. If the humidity level is really low, you'll feel colder than if it's inside this range. If the humidity is really high, you'll feel colder. And damp. Many of us have more problems being on the high humidity end of things than those of you in the desert. Our area averages over 80% humidity outside this time of year.

So, every year, one of the questions people ask during the Freeze Yer Buns Challenge is in regards to the issue with condensation and mold and what to do about it. Well, you have a few options. You can turn the heat up, you can lower the humidity with a dehumidifier or you can just bear with it.

As for condensation, it all really comes down to relative humidity compared to the outside. The University of MN came up with some guidelines for the recommended humidity levels for houses (bear in mind these are for 70 degree indoor temps):

Outside Temperature     Inside Humidity
20º to 40ºFNot over 40%
10º to 20ºFNot over 35%
0º to 10ºFNot over 30%
-10º to 0ºFNot over 25%
-20º to –10ºFNot over 20%
-20ºF or belowNot over 15%

Since a given volume of air can only hold so much water vapor at a given temperature, one way to remove the condensation issue is to raise the temperature. The warmer the air, the more water vapor it can hold, which means the less is hanging onto your windows and walls. Of course, this kind of defeats the purpose of this challenge.

Usually, we just deal with the condensation problem. But this year, because we've had more problems with condensation and I'm sick of fighting the mold, I invested in a dehumidifier. Not too shockingly, when I started it up in our bedroom after using the shower, the humidity was 90%. It's a neat little appliance on rollers so I've been moving it from room to room to reduce the humidity. It sucks water out of the air like there's no tomorrow. My son's room is also a haven for moisture collection and, after running it for a few hours, it collects several cups of water.

So, instead of living in a terrarium, our windows are looking a lot drier. I'm assuming that we won't have to run it as often once the general humidity is lowered overall but, with showers, cooking and just breathing, fighting the humidity is a never-ending battle around these parts.

Do you have a problem with moisture build-up and condensation in your home? How do you deal with it? Do you notice if it's worse when you keep the thermostat lower?


Annie Jones said...

I live in Missouri. Humidity is more or less a summertime problem here. In the winter, we use a humidifer to add humidity to the air so that we feel warmer and so there is less static electricity in our clothing, hair, carpeting, etc.

That said, we do have some moisture build up around on our kitchen window and sliding patio door when I cook. Those are the only problem areas.

Anna M said...

We have definite condensation problems due to my business, dyeing fiber and yarn. Since we also run a wood stove it hasn't been too bad in years past but this year seems to be different. I'm not sure if it's Vermont's "wettest year on record" or just the sheer amount of moisture in the air but we have been talking about purchasing a dehumidifier. I've bookmarked the one you linked to and will talk to my husband about it. I'm worried about mold but more worried about the condensation freezing on the windows and then rotting the wood (old house, old windows).

Humidity here has been horrible this year and I can't wait to move.

Lisa Under the Redwoods said...

We always have a humidity problem due to our wet weather and the fact that we keep the house fairly cool in the winter. We run a dehumidifier but it won't work if the room temperature is too low. We also open the windows a lot during the day. Around here it is often warmer outside than inside in the middle of the day.

Adrienne said...

This is completely a regional thing. I live in Kansas. Anything less than 50% humidity feels too dry to me. It's really humid in the summer, but in the winter, between it being dryer naturally and the heat running and drying everything out further, it's WAY TOO DRY. (Even with the heat at a relatively low setting, it runs a lot when it's really really cold out, which is usually all of January and February.) I run a humidifier constantly to just to prevent my skin from drying up and cracking off. I constantly electrocute myself with static. People get nosebleeds b/c it's so dry. What I'm saying is, definitely no humidity problem here. I do get some condensation on the windows when it's super cold out but I think that's just b/c they're so poorly insulated.

Wendy said...

The short answer to your question is "yes" we have condensation problems, but only at night. During the day, especially if the sun is out, there's no condensation on the windows.

We don't do anything about it. I have noticed, though, if we're using the woodstove, the air is both drier and warmer, and there are no issues with condensation.

Laura said...

Oh, shoot! You mean, I need to buy a humidifier? I am in semi-arid locale and the humidity is often under 25%. :/

Jonalynn said...

We have definitely had this problem. I had to call a mold remediation specialist last year because it was getting so bad. First thing he told me was to run the dehumidifier and turn up the heat! We have had the rainiest year on record and already have mold. This past week when I was canning, we actually had drops of water coming off the ceilings! I was also told to check our insulation. It appears that our lack of makes the problem worse.

Michelle said...

Here in Western Massachusetts, I run two dehumidifiers in my basement in the summer. In the winter, once the heat goes on, low humidity is more often the problem. We've been known to raise sparks off the dogs in the winter! I solved this by installing clotheslines in the basement. I use a fan to keep the air moving. No more sparks on dogs. I have noticed, however, that I do get condensation on the windows under the quilted window coverings. Not too bad on the main floor, but in the upstairs bedrooms, clean-up in the spring is pretty yucky.

Karin said...

Even here in the Pacific NW, at the peak of winter heating, we get nosebleeds and dry skin from low relative humidity inside, and we keep the heat below 62. Maybe we're just sensitive. I don't really get it since we're in the forest and have a load of leaky windows (that do get the shrink-wrap treatment in the fall). In terms of moisture, the fall seems the worst time for us; in addition to the start of the rainy season we're also "cooking out" the moisture that's accumulated since we last heated.

When we remodeled the bathroom, we installed a combo light-fan-heater overhead. The fan, of course, does a yeoman's job of expelling moisture. But the heater has been the stand-out for me. It doesn't take much to warm up the tiny room, and yet when one steps out of the shower, ooh-la-la! I do dream of a better exhaust fan in the kitchen to deal with moisture from canning.

The relative comfort of a home where the temps are kept low also has to do, I think, with how warm the home appears to be. As the season grows darker and the rains begin, we definitely light more candles, use the fireplace insert as much for its cheer as for heat, scatter more blankies, turn on more lights (CFLs of course!), and engage in more communal pursuits: coffee table meals, cuddling, read-alouds, board games, and--before this seems all too wholesome--serial dramas viewed on the glowing orb of the Energy Star LCD monitor!

JessE @ Love Life From Scratch said...

This reminds me of our humidity issue. We are exactly the opposite. Our thermostat is kept at ~55F at night and during the day when we are not around, then ~60F when we are home. We supplement with a wood burner, so this takes a lot of humidity out of the air. I get bloody noses in the winter when the humidity is low, so we started running a humidifier in the bedroom at night. Problem was, the outside corner of the bedroom was not insulated well, and mold began growing. We were able to come to the solution of using a timer to run the humidifier for only a few hours each night. Less mold, no static shock when petting the dog and no bloody noses!

Anonymous said...

Another Seattleite here. Seems a bit counterproductive to turn down the thermostat and then run a dehumidifier, so we use a myriad of tricks.

I try to balance the moisture in the house by opening doors and windows on drier days, not doing high-moisture tasks (like canning or all-day soups) when it is already raining outside, keeping showers short, and using the fireplace. I also keep shrubs around the house perimeter to a minimum, chose evergreens over deciduous, and rake up leaves that fall in the yard - they hold a lot of water and get tracked into the house.

We installed good windows (double pane, vinyl frame) and extra insulation wherever we could. The larger windows have insulated curtains. We do still get a touch of condensation now and then, but it's not bad at all.

Greenpa said...

Not to be fussy or anything- but what's the power consumption on your dehumidifier?

Googling that, I get a number of ~ 785 watts; where a double electric blanket ~ 100 watts.

If you've got the heat turned down to save power- I think we need to start figuring in the additional inputs here. And don't forget- if you're running a 785 watt machine inside- it's adding that much heat to the room, too-

If only it were all simple. :-)

Another root cause of the condensation is that new construction houses typically are much "tighter" than old; specifically to save heating/cooling costs. But- that greatly decreased air exchange has ramifications, that you really can't ignore. One possible response is to add a ventilator with a heat exchanger- more fresh air; but it's not free, either money or energy-wise, either.

Rainy Day Gardener said...

With a home built in 1924, I can't say we have condensation problems. Drafts, yes. We put new windows in a few years back and that made a big difference, but overall, it's still a drafty old house.

Crunchy Chicken said...

Oh, Greenpa, a liklik binky isn't going to solve the humidity problem. Sure it will keep me more warm, but won't help the dampness feeling. And, you know me, I've already accounted for additional inputs.

Anyway, our furnace is oil heat which is expensive ($4+/gallon). Compared to our dirt cheap electricity rates ($0.046 per kWh), running a space heater or dehumidifier is pennies in comparison.

Jenni - Yeah, in our old 1916 house in Phinney Ridge we never had a problem. But, then again, we could feel the wind in half the rooms.

Anonymous said...

It's humid as all get out here, but since we heat primarily with wood, that takes care of it. Before we installed the wood stove, we looked into dehumidifiers, but our electric rates are insane (.20/kWh) and dehumidifiers are kinda hogs, so it would have been cost prohibitive to run it.

EngineerChic said...

We have a gas range and I think it contributes to the humidity problem as well. We run a dehumidifier in the basement year round, it works great and really helps.

Given the choice of using more energy or risking mold/mildew allergies ... I'd use more energy and look for some other way to cut down. Then again, I fly a lot for work so I have other sins to atone for first.

Cold House Journal said...

Around here, most people keep their homes so heated in winter that they are more worried about too little humidity, rather than too much. They go to lengths to evaporate more moisture into the air using humidifiers, kettles on the wood stove, buckets behind the radiator, etc.

We keep our house chilly enough that it stays plenty humid, and parts would probably would be too humid if we didn't extract some out of the bathroom with a mini-dehumidifier. The great news about a dehumidifier in winter is that through the miracle of condensation, it gives back about twice as much in heat as it consumes in electricity. (See

Anonymous said...

I've been w/o a proper heat source (tiny house, candles and kerosene lamps & large dog body do okay) So far lots of condensation on single pane windows. I wipe them down with tea towels and dry the towels outside.

Will get stove next week & I expect all will improve.

Rosa said...

I'm in Minnesota, and it's a summertime problem here too - we had a real problem this summer the weeks it was 100 degrees, with condensation on the basement stairs where the cooler air met hot upstairs air.

But one solution for condensation is insulation. We got half our windows replaced last year, and when I was canning (in October. Tomatos got cheap her halfway through October this year instead of August) I noticed that all of the old windows fogged up and none of the new windows did.