Humidity levels in the house

[ikessky]

Apparently my house became the topic of conversation at one of my family's gatherings while I wasn't there. My grandpa got all nervous about the condensation that I get on my windows, so he brought over a little humidity meter (the ones with a "comfort zone" of what seems to be 30-55% on the indicator). Before we get to the actual readings, I should say that I know my windows aren't good. They are single pane with storm windows, but since I've been burning wood and the house gets so warm, I don't put the storms on anymore. I've basically just decided that we have such bad condensation because of the single pane and the fact that they don't really open and shut so well any more.

On the main level with no heat source running, the little humidistat will remain in the mid to high comfort zone. Running the wood furnace or the NG furnace rarely results in it's moving.
In the basement with no heat source running, the level will usually fall to the low or even dip into the dry range.

I guess the question I really have is, should I be worried that I'm not in the dry zone when it's winter and I'm burning wood? There is no condensation anywhere except for the windows, so I don't feel like we have a high humidity problem. I guess I've just come to the conclusion that the windows suck and that's all there is to it. I guess to rule them out, I could wipe them all down really well and put the storms back on and see what the levels do.

Anyone have any thoughts or concerns?

 

[Highbeam]

If anything, the water condensing on the windows is helping to dry your air out. They are doing just what a dehumidifier would do. Single pane windows touch the cold air on one side and the hot inside air on the other. Just like a can of coke, water will always condense on that window if it is cold enough outside. You will likely even see it freeze on cold nights. Also, the leakiness is helping to dehumidify your home by introducing cold and dry outside air.

Depending on the size of your home, the number of people spewing moisture with each breath, your cooking habits, and your bathroom ventilation scheme, your humidity levels are probably just fine. Are you really upset to be in the "comfortable" zone?

 

[jockum]

Even with good windows, you will get the condensation because they are the coldest surface. Myself, I have to run my furnace fan on manual when I am burning, with the humidistat on 100% humidity so it doesnt get too dry, I try to keep at least 50-60% humidity at all times, its more comfortable, and oh yeah, the humidity actually makes the air feel warmer. (IMO)

 

[ikessky]

No, I'm not upset to be in the "comfortable" zone. I just got a little worried when I heard they were all talking about how it's not normal to burn wood and not have a house that is too dry.

I know some condensation is unavoidable, but we have a couple windows where you cannot see out of them and the water runs down and pools on the wood sills. Most of them have been stained because of this and we end up having to clean up mold on the windows. This would be the main reason that I want to replace the windows. I doubt that breathing in that mold is very good for any of us (no matter how small of an amount it is!).

 

[Wood Duck]

Is see you have a forced air wood furnace. Is this one of those units where the firebox is outside, or is the firebox supplied with outside air? If you are burning outside air, then your setup is not the same as a typical wood burner using inside air, so I wouldn't expect it to have the same effect on inside humidity. I assume your forced air system keeps recirculating the same indoor air. If this is the case, i don't see why your system would have any more influence on inside humidity than any other furnace.

 

[ikessky]

My wood furnace is in the basement and I do not have an outside air supply going to it. Nor is it hooked up to my return air system. The wood furnace blower is taking in air from my basement and any other air that it can pull down the stairs from my main level. My NG furnace is also in the basement, but it is getting it's combustion air from outside. Whether I'm burning my wood furnace or my gas furnace, the humidity level doesn't seem to change.

The other thing I should mention is that I keep more than a cord of wood in the furnace room. I'm sure this also contributes to some humidity in the house as it is not kiln dried or 0% moisture.

In the summer, we run a dehumidifier in the basement which alieviates the "basement" smell and the guage on that (for what it's worth) will usually get down to 30-40.

I guess the long and the short of it is that I should look at this as a small blessing? I do have dry skin and the kids often wake up with sore throats, so I don't think the little humidistat is really showing an accurate picture of what's going on in the house.

 

[Renovation]

My wood furnace is in the basement and I do not have an outside air supply going to it. Nor is it hooked up to my return air system. The wood furnace blower is taking in air from my basement and any other air that it can pull down the stairs from my main level. My NG furnace is also in the basement, but it is getting it's combustion air from outside. Whether I'm burning my wood furnace or my gas furnace, the humidity level doesn't seem to change.

The other thing I should mention is that I keep more than a cord of wood in the furnace room. I'm sure this also contributes to some humidity in the house as it is not kiln dried or 0% moisture.

In the summer, we run a dehumidifier in the basement which alieviates the "basement" smell and the guage on that (for what it's worth) will usually get down to 30-40.

I guess the long and the short of it is that I should look at this as a small blessing? I do have dry skin and the kids often wake up with sore throats, so I don't think the little humidistat is really showing an accurate picture of what's going on in the house.

Hi!

30% to 50% humidity is considered the comfort range, with 45% ideal. Above 50% is considered a risk for growing mold, etc, below 30% more risk of dry skin and sinuses.

You and others are correct that poorly-insulating windows are cold, and condensation on them is not a sign of excessive humidity.

I guess the take-aways are that wet windows don't mean your house is too humid, and are a sign that your window glass leaks heat.

 

[Highbeam]

Even with good windows, you will get the condensation because they are the coldest surface.

Absolutely false in my experience. I replaced loose aluminum framed single pane windows in my home with modern vinyl double pane windows a few years back. We used to have lots of condensation just like the OP with puddles in the sill. Now, same temp in the house, we get zero condensation nomatter what the outside temp is. True, the windows are a large loss of heat but not like the old days.

 

[LLigetfa]

Put up the storm windows! All that condensation is likely getting into the walls under the windows and rotting them out, and mold spores are probably being dispersed by the infiltrating air.

 

[jockum]

highbeam: not to pick an argument, but moisture in the house will condense on the coldest surface it can find. Your new windows are obviously higher r value than the old ones, but depending on the air space in between the panes may not be any better than a double pane insulated unit with 3/4-1" spacing and an insulated spacer. You may also have other areas colder than your glass where condensation is occuring, or you just may have very little water vapor in the house. My windows are 1" insulated with low e and argon gas in between and have one of the highest r and u values, and I get the condensation because I intentionally pump in the moisture via my humidifier when I am burning to replenish it. Even with the triple panes, the r value of any window is substantially less than a standard or even sub standard wall.I have replaced thousands of replacement windows, and almost always get the phone call that " my windows have moisture/condensate on them".In almost every case, its because the old windows were so inefficient, or leaky, that moisture would never collect on them. .And I am not trying to offend anyone, but I have also built a couple hundred houses with everything fro Pella, Anderson, Hurd, Certainteed, Jeld Wen,and Simonton windows and others, and the Andersons and Pellas were the leakiest and had the highest seal failures of them all. Just my 2 cents.

 

[ikessky]

Put up the storm windows! All that condensation is likely getting into the walls under the windows and rotting them out, and mold spores are probably being dispersed by the infiltrating air.

Let 'em rot! We're installing new windows. The leaking air in the winter is fine, but what is happening when it's summer? I'm probably spending more in AC than I really need to. Besides, right now, I cannot open any of my current windows (frozen shut, expansion/contraction, etc). With new windows, I would lock in more heat, but it would be easier to crack open a window and cool things down.

 

[wkpoor]

Somewhere on the net there is a chart for indoor humidity vs outside air temp. Unless you install triple glazing with krypton you can see condensation on good glass in below freezing conditions. Just simply measure the surface temp of any window and with a chart you can figure the dew point of that surface. Anyone that says their house has 45% humidty at 20 degreeF outside temp and the windows are dry has got their numbers wrong somewhere unless they have the latest and greatest U factor window which 99% of us don't. My house runs abour 35% and I have a moisture problem on double pane. I installed a couple triples and they don't sweat.

 

[Renovation]

Even with good windows, you will get the condensation because they are the coldest surface.

Absolutely false in my experience. I replaced loose aluminum framed single pane windows in my home with modern vinyl double pane windows a few years back. We used to have lots of condensation just like the OP with puddles in the sill. Now, same temp in the house, we get zero condensation nomatter what the outside temp is. True, the windows are a large loss of heat but not like the old days.

+1 Absolutely. Quality window manufacturers make a big deal of this, with false-color pictures of how much warmer their window glass are than poor insulating windows, and how that reduces condensation.

 

[LLigetfa]

Put up the storm windows! All that condensation is likely getting into the walls under the windows and rotting them out, and mold spores are probably being dispersed by the infiltrating air.

Let 'em rot! We're installing new windows. The leaking air in the winter is fine, but what is happening when it's summer? I'm probably spending more in AC than I really need to. Besides, right now, I cannot open any of my current windows (frozen shut, expansion/contraction, etc). With new windows, I would lock in more heat, but it would be easier to crack open a window and cool things down.

Fine if it were just the windows rotting but I'm sure the water is getting down into the wall and rotting it too. Then there is all the mold in the walls...

 

[woodgeek]

Water vapor condenses on surfaces below the dew point, which depends simply on the relative humidity, RH. You can look up the numbers. Even if your windows are the coldest part of your interior, if they are above the dew point, there will be no condensation.

In all but the most airtight houses, the RH is limited by the continuous air leakage out of the house, typically changing all the air in your house every hour or two. If that vapor leaks out without 'seeing' a surface below the dew point, it will leave your house in a vapor form. This is the purpose of having a vapor barrier on the warm side of the insulation (in cold climates) so it can't reach the cold side of the thermal envelope and condense in the wall space. The little vapor that leaks through the vapor barrier get _diluted_ by the outside (dry) air that is 'washing' the structure outside the vapor barrier, pushing down the RH so that again, it will not condense out even at the lower temp. Exterior 'house wrap' is designed to block bulk air flow (to save energy), while still being permeable enough to vapor to allow this water vapor dilution, so defects in the interior vapor barrier do not lead to a condensation problem (e.g. under the house wrap).

In an airtight home, we could imagine that the RH would just keep rising and rising (as emitted water has nowhere to go) until the dew point reaches the temp of the coldest surface (wherever that is). For the few folks that have a house that is too humid in the winter, they should really get a Heat Recovery Ventilator to provide adequate fresh air. Installed correctly, that ventilation should suffice to keep RH in the comfort zone.

In my (leaky) case, much of the leakage is through my double hung windows with storms. The inner pane is warm enough to not dew up, but I sometimes get condensation on the outer pane (on upper story windows only, as those are the 'exit windows'). I don't worry about that water, as it escapes to the exterior through the weep holes designed in the window.

 

[ikessky]

Fine if it were just the windows rotting but I'm sure the water is getting down into the wall and rotting it too. Then there is all the mold in the walls...

It's certainly not close to the rotting point, I can tell you that. I was being a little sarcastic. Although most all the windows have condensation on them, it is only one that runs really bad. We are looking to replace them this spring.

Just a fun little tid bit, this AM I was showing around 40-45% in the house and weather.com is showing 85% humidity outside for my area.

 

[nate379]

I have the chart on my home computer. Don't remember exactly, but somewhere around 20-30% for most winter temps was recomended.

I know in my house if I let it get over 30% the windows will sweat pretty bad when it's close to 0* or below.

I don't have top end windows, but they aren't cheapos either.

My folks put in high end windows (thick double pane) in their house a few years ago and they sweat worse than the 25yr old cheap wood windows that where there before!

Somewhere on the net there is a chart for indoor humidity vs outside air temp. Unless you install triple glazing with krypton you can see condensation on good glass in below freezing conditions. Just simply measure the surface temp of any window and with a chart you can figure the dew point of that surface. Anyone that says their house has 45% humidty at 20 degreeF outside temp and the windows are dry has got their numbers wrong somewhere unless they have the latest and greatest U factor window which 99% of us don't. My house runs abour 35% and I have a moisture problem on double pane. I installed a couple triples and they don't sweat.

 

[woodgeek]

Fine if it were just the windows rotting but I'm sure the water is getting down into the wall and rotting it too. Then there is all the mold in the walls...

It's certainly not close to the rotting point, I can tell you that. I was being a little sarcastic. Although most all the windows have condensation on them, it is only one that runs really bad. We are looking to replace them this spring.

Just a fun little tid bit, this AM I was showing around 40-45% in the house and weather.com is showing 85% humidity outside for my area.

The confusing thing about RH is that it depends on temperature. If you grabbed a bag of that cold outside air at 85% RH, and brought it into the house and warmed it up to 70°F (without any of the gas or vapor inside escaping) the RH of the air would now probably be <20% RH, just like magic. Apologies if this was clear to you already.

I looked it up once, and found that 100%RH at 32°F (e.g. freezing rain and wet snow conditions) has the same amount of water per volume of air as 70°F air at ~25% RH. If it is 85% RH at 32°F outside, your house will tend towards 0.85*25% = 21%RH inside, if you don't add any water to the air.

 

[bboulier]

Ikessy, You are making a wise choice to replace the windows. We had a similar problem a few years back in our 1957 split level. Once the original windows (aluminum frames, single pane) were replaced, we had a dramatic improvement in comfort levels and fuel bills (winter and summer).

 

[pyper]

Burning wood won't change the humidity level per se. But burning wood will draw air into the house from the relatively dry outdoors. Our house isn't particularly dry. Maybe they're thinking that your stove should have the same effect as a fireplace?

I think you're a lot more likely to cause rot problems with storm windows. Our house had them, and they caused a lot of rot on the sills between the window and the storm, because the prior owner didn't keep the weep holes clear. When condensation drips down onto the sill or the stool, as long as you don't see rot on the surface, I don't think you need to worry at all about water traveling through the solid wood piece and getting down into the walls.