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Baseboard Heat Causing Hunidity Probs?

AlwaysLate's picture

I've got an old house that we've extensively insulated. The last thing we did was to have spray foam insulation installed on the underside of the roof deck. We have a finished attic space and were getting awful ice dams before the spray foam. Ever since the foam was installed (Mar 2007), we've had condensation on many of our windows. They are all double pane- some vinyl replacement, some Pella, and some Andersen 200 series. I've been trying to take care of potential issues in the cellar (dirt crawlspace with no vapor barrier for one). The vapor barrier has reduced the problem but we still have condensation. The house is in Syracuse NY BTW.


Today I had a fireplace installation company over to talk about putting in a vented gas fireplace. I was telling them about the condensation issue and they said it was due to the hot water baseboard radiator. That's a new one to me. I asked how that could be since the copper is watertight. He didn't have a technical answer but seemed confident that was the culprit. Anyone heard that before?

(post #115530, reply #1 of 35)

Yeah, hot water is "moist" heat and forced-air heat "dries out the air". We've heard it all before, but it's bunk.

What you've done is tighten up the house substantially, and now there's much less "exchange" of the air (ie, fewer drafts). So moisture generated in the house (from showers, cooking, breathing, etc) and moisture from the cellar is collecting in the house rather than being "vented".

It's not clear how much condensation you're experiencing, but "some" is normal during cold weather in any cold climate, and especially when the outside temperature suddenly dips. But if the moisture is dripping down and puddling at the window sill then you have too much and need to take more steps to fix it.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #3 of 35)

Yeah, hot water is "moist" heat and forced-air heat "dries out the air". We've heard it all before, but it's bunk.


Agreed.  I've always wondered where all of that moisture that forced air systems supposedly remove from the air actually goes.

(post #115530, reply #29 of 35)

I think there's some truth to the idea that forced air systems "dry out the air."  What's important in this situation is "relative humidity," the amount of water the air contains relative the amount it could hold if it were saturated (100% RH), just short of turning into fog or condensation. 


Besides RH, the other variable is temperature- a room full of hot air can hold a lot more water than the same room full of cold air.  That's why on a hot, humid day, you get condensation on a cold beer- it cools the air next to it, the air can't hold as much moisture and it condenses on the side of the can.  Or similarly, when warm, relatively moist air is next to a cold window, its temperature drops, its relative humidity rises over 100 and you get condensation. 


Now, how does that relate to forced air?  Normally, every house gets some make-up air, usually from infiltration, which in winter is colder than the inside air.  So cold air comes in, gets warmed and its relative humidity goes down- what might have been 50% RH at 32 degrees might be 20% at 68 degrees.  Still the same absolute amount of water in the air, but lower RH, because the warm air can absorb more water and a forced air system blows that relatively dry air all over everything..


Now, why is that so much different than say, hydronic heat- the make-up air still gets warmed up, so it should see the same drop in RH.  Good question- my answer is that most forced air systems leak horribly- some of them as much as 20%- and often that leakage goes into an unconditioned space- attic or crawl space, so all the leaked conditioned air has to be made up with outside air.

(post #115530, reply #30 of 35)

...most forced air systems leak horribly- some of them as much as 20%- and often that leakage goes into an unconditioned space- attic or crawl space, so all the leaked conditioned air has to be made up with outside air.


Yes, in this instance a forced air system will dry out the air more than hot water systems.  I hadn't considered that scenario.  It may or may not be significant depending on the specific system, but I suspect that the perception that forced air systems "dry" the air is due more to the the belief that warm air is dry air.  In terms of RH it is, but it still has the same amount of moisture in it.

(post #115530, reply #2 of 35)

Do you have and use a good bath fan and kitchen hood vent?


The old "hydronic is moist heat" thing always makes me shake my head.  If it was moist heat, you'd have a leak.

(post #115530, reply #4 of 35)

Ha! That's funny and a good way of looking at it. I was surprised to hear the concept that copper plumbing was "radiating" moisture into my house. I have vent fans in the bathrooms. The vents are ducted to the outside. The kitchen range hood is not however. I know it is advisable to vent to the outside but difficult due to location.


There is quite a bit of condensation- probably the lower 1 or 2 inches of glass in each sash has water droplets forming. The house doesn't feel humid but it seems there's a problem. I borrowed one of those electronic weather stations and was getting relative humidity readings of 35-45%. From what I've read, that's not that high but again, condensation on the windows is telling. I've got a dehumidifier in the cellar that runs nonstop. It has a digital control on it and I've got it set at 45% and it can never get the RH to below that.


I'm going to pick up a more sophisticated RH meter and try it on the different floors (including cellar) to see if I can see where the problem is. This is a real bear to figure out. I can't tell where the problem is but am seeing the symptons. Thanks for the input by the way.

(post #115530, reply #6 of 35)

A "fog" on the bottom 2-3 inches would be kind of the "target" around here (MN) for the colder days of winter. But that would be an RH around 25% when it's maybe -10F outside.

Normally 40% should be the max wintertime RH in a house (and one that's only achieved in older homes by use of a humidifier), and that value should reduce as the temp drops below 30-35F. If you're getting readings above 40% then you have a humidity problem in the house, possibly due to the cellar.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #7 of 35)

BTW, this might be the ideal place for one of those cellar vent fans that are sold in magazine ads. They're a unit with fan and humidistat and a "snorkel" duct that reaches up to a basement window. They draw the cool moist air from near the floor and exhaust it. Energy-wise probably more efficient than a dehumidifier, even though you do have to pay to heat the replacement air.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #8 of 35)

But that does bring up another point, mostly unrelated to your humidity problem: If you've sealed the house that well you may be impeding the draft of your furnace or water heater. You need to assure that any combustion appliances are getting sufficient make-up air.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #9 of 35)

Thanks again all for the input. The boiler is a sealed combustion unit that draws from outside and the hot water is provided by a standby tank from the boiler. I'm amazed at how many humidity posts there are on Breaktime right now. I saw someone else talking about a heat recovery ventilator. Maybe I need to talk with a local HVAC contractor to see if they have any ideas.

(post #115530, reply #13 of 35)

That unvented range hood may be a major culprit. Cooking puts off a lot of moisture that needs to go somewhere.

Another (often unrecognized) moisture source is houseplants. Have you ever noticed the amount of moisture that builds up in a garden window?

(post #115530, reply #5 of 35)

Fire the gas fireplace company for giving you bogus information!


A closed hot water system adds no moisture to the air (unless there is a leak).


You need to finish your handywork of sealing your house up with a ventilation system/strategy that will now control the fact that you are now trapping a lot of moisture that you were previously allowing to dissipate through natural forces of wind, thermal forces, and vapor pressure. Now look at your exhaust fans and the controls ... consider your options. Ventilate (i.e. exhaust) intelligently and your insulation system will be a success. You are half there ... now finish the hard work you started.

There ain't NO free lunch. Not no how, not no where!

(post #115530, reply #10 of 35)

You're probably right and thanks for the optimism. After 8 years of nonstop renovation, it's getting harder and harder to see the silver lining. By the way, a coworker had some foam insulation work done by the same contractor that I hired and they told him that they are now required to install automatic timers on bathroom vent fans when they install foam insulation to address IAQ issues. Apparently some requirement from New York State. That just rails against common sense. Spending thousands on a premier insulation job to increase energy efficiency and then needing to run exhaust fans for hours. Sounds like an HRV or similar might be the next improvement! 

(post #115530, reply #11 of 35)

Normally you can't retrofit an old house tight enough to create wintertime humidity problems. I strongly suspect that your problem is that cellar.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #12 of 35)

Yea, your moisture is not coming from your baseboard heat system unless it's leaking somewhere within the building, basement and or one or more rooms! You would see dripping water and steam if it were. How's the boiler down in the basement, I assume you do have a basement boiler/heater. I'm not familiar with the term "vented gas fireplace" but if that's like a gas fired fireplace insert, that's not likely the source since it's completely enclosed.

The moisture is not coming from the crawl space under the house unless you observe standing water down there. Interior moisture comes from three main area/activities, the kitchen, bathroom/laundry and possible heating methods. The only way baseboard heating could generate significant moisture would be a direct water leak in the heated water circuit or incorrect, disconnected, venting of heater combustion gasses. Combustion gas sources aren't likely because if there were that much moisture coming from the boiler system you would be getting huge quantities of carbon monoxide/dioxide also and you would have found and corrected that by now.

Are you venting a clothes dryer properly, outside the house and no leaks in the vent pipe? Bathrooms/shower areas vented to outdoors, not into basement or within the building envelope? Your not running a soup kitchen and boiling large quantities of water to make pasta are you?

(post #115530, reply #14 of 35)

I don't know if anyone's mentioned your windows themselves.  I have Andersen 200 series in my house with a 3/8" gap between panes, and they get a fair amount of condensation on them.  If the inside surface of the glass was warmer, you would not get condensation.  After you seal up the basement better, you might look more closely at your windows.

(post #115530, reply #15 of 35)

Thanks. Hopefully it's not the windows. I just put five of them in a few years ago. I have another room with eight 200 series with Low E and those don't seem to have the condensation. Not sure if it's because that room has lower humidity or if it's the Low E. I noticed that the condensation is worst in the morning and seems to go away through the day. Maybe that's due to the cooler nighttime temps in the house allowing moisture to condense and the higher daytime temps allow the moisture to be pulled back into the air. I have a lot of theories... The problem is eliminating probably causes can get costly.

(post #115530, reply #16 of 35)

Nighttime lows do cause more condensation, and sunlight radiation will heat up the glass.  What side of the house has the worst condensation issues?  Do the kitchen and bath have the worst problems?  Is the basement space the same under the whole house?

(post #115530, reply #17 of 35)

There doesn't seem to be a pattern regarding exposure. Windows on various sides have condensation. Like I mentioned in an earlier post, I have several types of windows (Andersen, Pella, and unknown mfg vinyl inserts) that have the problem. The windows in the upstairs bath do have condensation but so do the bedroom windows on that floor.


The basement is the same construction except under an enclosed porch, where there is a crawl space. I just installed a vapor barrier on the dirt a few weeks ago and insulated the perimeter walls with 2" foam board. The windows in the enclosed porch have shown no condensation issues- even before I installed the vapor barrier. That always seemed strange to me. Another strange thing is that all the floors seem to have the problem except for the basement. Like the rest of the house, the basement windows are double pane but do not seem to have condensation issues. 

(post #115530, reply #18 of 35)

Keep in mind that windows with curtains will have more condensation than windows without curtains. Basement windows may have less condensation because it's warmer near the ground where there's little wind or convection.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #27 of 35)

I was thinking that if the basement windows aren't condensing, maybe the source of the moisture isn't in the basement. The basement itself is, of course, typically cooler than the rest of the house (maybe about 60 degrees) so, based on one person's scientific discussion of RH and humidity, a given amount of moisture in a cubic foot of air would be worse (higher in RH and closer to the dew point) if that cubic foot of air were cooler (i.e., like in the basement). If this is true and I'm not seeing condensation in the basement, maybe the moisture problem is from one of the floors above?


In terms of how much the tighter the house is, the insulation contractor did a before and after blower door test. I believe the "before" number was about 3,200 cfm and the "after" number was about 1,800 cfm. So almost a 50% reduction.


Both bathrooms have exhaust fans vented to the outside but, as I mentioned earlier in response to someone else's question, the range hood is not. I do agree that a lot of moisture is coming from cooking. You can see the fogging on the windows when dinner is underway. That might be the next reasonable step- converting the hood over to an outside vent. I just hate the thought of cutting through the cherry cabinets. Then again, I hate the thought of doing nothing even more. And thanks again to those that have responded. I appreciate the suggestions.

(post #115530, reply #20 of 35)

Are you looking to declare your nice windows a problem? Night outside air is cooler ... so is the inside air ... which the RH goes up when it is cooler ... bingo ... condensation on your windows. Daytime outside is warmer and so is inside ... higher surface temp ... no condensation.


Why do new windows condense when the old single panes don't? Or why do they now condense after just doing all my other energy work (foam insulation, sealing, caulking, etc.)? You have likely reduced your air leakage in a significant way ... which ensures a higher RH in the house ... raising the dewpoint temp.


I've seen it happen a few times ... brand new windows and NOW there is condensation ... go figure. Reduced air leakage. Need to ventilate a little more to compensate.

There ain't NO free lunch. Not no how, not no where!

(post #115530, reply #21 of 35)

It may even be that leakage through the windows has been reduced, and the leakage around the windows was keeping the microclimate humidity low.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #22 of 35)

But I'll repeat: From the general description of the house I'm getting, you would not normally be able to tighten it up enough to make humidity a problem, so likely there is an "unusual" moisture source in the house, such as the cellar.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #24 of 35)

Did I miss something? I thought that was what he was doing ... tightening up the house ... and as you said yourself in your previous statement, replacing the windows affects the tightness of the house.


I've seen a situation where all these people did was replace several windows in the living room of their classic '70s rancher and ... had condensation. These were low E replacements for the old single pane windows. Interviews with them revealed nothing else unusual about any other changes in their house (e.g. habits, sealing, etc).


Moisture issues can cause us to scratch our heads sometimes.

There ain't NO free lunch. Not no how, not no where!

(post #115530, reply #25 of 35)

I'm just saying that there probably is an "unusual" moisture source at work here, vs simply a "too tight" house. Before bludgeoning the problem to death with an HRV the causes of the excess moisture should be treated, possibly with selective ventilation of the cellar, eg.


The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115530, reply #19 of 35)

This is a rather long explanation, and I have posted versions of it here before, but people have told me that they find it helpful, so I will post it again.  Hopefully, you find some value in it...


You have interior condensation on your windows simply because the surface temperature of the window is below the dew point temperature of the air in your home…that’s it…a very simple explanation.


 


Unfortunately, as to why the surface temperature of your window (glass) is below the dew point temperature of the air in your home may be a bit more complex – so I am going to offer a few thoughts and maybe even throw in a few numbers that I hope might help your situation.


 


In the summer, when you pull something cold and refreshing out of the refrigerator, and the air is warm and humid, that cold and refreshing beverage container suddenly and quite magically becomes instantly wet – just as soon as it is exposed to the air.  What has happened is that the temperature of the container fresh from the refrigerator is below the dew point temperature of the air – which has caused condensation on the outside of that container.


 


What happens to your windows in the fall and winter is that the surface of the glass is below the dew point temperature of the air in your home – which is causing condensation on the surface of that glass.


 


Dew point is defined as saturation vapor density...or put in simpler terms, when the air reaches 100% relative humidity and can hold no more moisture.


 


Relative humidity is, well, relative. 


 


Relative humidity is a comparison of the actual vapor density versus the saturation vapor density at a particular temperature.  Put a bit more simply, dew point is 100% relative humidity or the point where the air - at that temperature - is no longer able to hold any more moisture. If the air has reached vapor saturation (100% relative humidity), then the air will release moisture...be it on the outside of that cold beverage container in the summer time, or be it on the interior glass surface of your windows in the winter time, it makes no difference.  If the surface temperature happens to be below freezing, then that moisture becomes frost or even ice.


 


In order to stop condensation from forming on the surface of a window, you either have to lower the dew point temperature of the air in your home to a level below the dew point temperature of the window surface, or you have to warm up the window surface to a temperature above the dew point temperature of your home, or a combination of both.


 


Lowering the relative humidity of the air in a home may have absolutely no effect on controlling window condensation or it may completely solve condensation problems, depending on how the relative humidity was lowered and what affect the “how” has on both the moisture level of the air and the temperature of the windows.  All this because there are two ways to lower relative humidity – first you can increase the air temperature or second you can decrease the moisture content of the air – both decrease relative humidity, but they are not the same. 


 


By increasing the air temperature in your home you will lower the relative humidity but you will not change the dew point – which is based on the amount of water vapor in the air and is not based on the temperature of the air.  So, while the RH is lower with higher air temperature, it may not effect condensation on window surfaces at all – unless the rise in air temperature also caused a corresponding rise in window glass temperature to a level above the dew point temperature.


 


But, lowering the amount of water vapor or moisture in your air will lower the dew point temperature as well.  And if it lowers the dew point temperature sufficiently to drop it below the temperature of your window glass – no more condensation issues.


 


The amount of moisture in the air is measured in grams per cubic meter, which is kind of nice for our metric folks but not so nice for our non-metric folks; but the metric version is much easier on the calculator than the English version.  However, in the interest of making this stuff easier to understand for all of us non-metric types, I am going to use Fahrenheit rather than Celsius temperatures in the calculations. 


 


Okay – consider your home at 65 degrees F and with a relative humidity reading of 40%.  There are 6.25 grams of water in a cubic meter of air in your home in that particular scenario - which then equates to a dew point temperature of 38 degrees F.   So at 38 degrees the air will be at 100% relative humidity or at saturation vapor density. 


 


Now, if your neighbor keeps her house at 75 degrees, but she also has 6.25 grams of water per cubic meter in her air, then the relative humidity in her home is 29% - versus your 40%. But, and here’s the kicker, the dew point temperature in her home is still 38 degrees. 


 


While the relative humidity in her home is much lower than is the relative humidity in yours; if the surface temperature of the windows in her home is 35 degrees she will have condensation on those windows…yet if the surface temperature of your windows is 40 degrees – only five degrees warmer – you will not have condensation on your windows.  


 


So, while her handy humidity gauge reads (correctly) only 29% RH – she has a condensation problem.


While your handy humidity gauge reads (correctly) 40% RH – you don’t have a condensation problem…SWEET…well, for you anyway, not her. 


 


If your home hygrometer measures the relative humidity in your home at 60% while the temperature of your home is 70 degrees, you will have a dew point temperature of about 51 degrees – meaning that if the temperature of the window surface is below 51 degrees then you will have condensation - so now we talk a little more specifically about windows.


 


The interior surface temperature of a single lite of glass, when the temperature outside is 0 degrees F and the inside air temperature is 70 degrees, will be about 16 degrees. 


 


Add a storm window on the outside and the surface temperature of the inside lite jumps up to about 43 degrees – a huge improvement.


  


But these are center-of-glass readings and not the temperature readings at the edge of the window where condensation usually forms.   A typical clear glass dual pane window is going to have center-of-glass temperature reading pretty much the same as a single pane with a storm – however, if that dual pane has a LowE coating and an argon gas infill then the center-of-glass temperature will be about 57 degrees – a 14 degree improvement over a clear glass dual pane or a single pane with storm window – but again, and more importantly, there will be a comparable edge of glass improvement as well, particularly if the IGU (Insulating Glass Unit) was manufactured using a warm edge spacer system.  Also, the dual pane is going to have desiccant between the glass layers.  Desiccant absorbs moisture keeping the inside of the dual pane system very dry. 


 


The advantage?  If it gets cold enough outside, the temperature in the airspace between the lites can get very low.  By keeping that space dry, it helps to keep the dew point temperature very low as well; something not always possible when using a single pane and storm window. 


 


Oddly enough, a single pane with a good and tight frame and sash assembly may be more prone to condensation than will a less tight single pane window simply because air (and moisture) will leak out of the looser window while the tighter window may be more likely to trap the moisture inside the home.  And, while a tight storm window can help the interior lite to avoid condensation (when compared with a single lite and no storm), the storm window itself may frost up when the temperature is low enough – at a temperature usually well above the temperature that will cause the dual pane to ice up.  It is unavoidable given the right circumstances


 


So what does a window temperature of 57 degrees mean?  Well, as I mentioned earlier a home kept at 70 degrees with a 60% relative humidity has a dew point temperature of 51 degrees so it is much less likely that there will be condensation problem on those particular windows than there would be with a less energy efficient window - despite the relatively high relative humidity in the home. 


 


But, there is always a "but"…


 


Again, that 57 degree glass temperature is still a center-of-glass reading and the edge of glass temperature will be lower - actual temperature is dependent on both the spacer system used in the IG unit construction and on the material used to construct the sash.  So even with a "57 degree" center-of-glass temperature it is still possible to get window condensation if there is enough moisture in the air.


 


And consider that the interior glass temperatures are based on the fact that moving, warmer, indoor air is actually in contact with the glass at a given time.  Curtains, shades, other obstructions can cause problems by blocking airflow across the glass – airflow that can have a huge effect on the condition of the window relating to condensation.  Also, bay and bow windows can be more prone to condensation – again because of the possibility of decreased airflow over the glass. 


 


And finally, what can happen to the dew point if you keep your home at 70 degrees and you have a 65% relative humidity?  Well, for one thing the dew point has jumped up to 57 degrees which we have already noted is the same as the window temperature.  For another thing, anyone with 65% relative humidity in a home at 70 degrees has way too much moisture in their air and they are in serious need of some sort of ventilation system – or at least several good exhaust fans!


 


 


 

(post #115530, reply #26 of 35)

I was Pm on a energy efficient Sip house a couple of years ago. They professor's wife did a lot of research and she was very happy with the house.. they had a 4 inch duct system to circulate air throughout the house and and an energy recovery ventilating suytem  to keep the moisture level down. 

(post #115530, reply #28 of 35)

Is that a typical situation for SIP construction (i.e., needing to provide a system to exchange air with the outside to compensate for the decrease in passive air leakage)? I figured with all the experience on Breaktime and with some seeming to have extensive experience with spray foam, I would be told that absolutely I have to install something like that to compensate but so far no one has said that so definitively. I'm curious if your experience with HRVs and SIP construction is typical. Any idea?

Window Condensation (post #115530, reply #32 of 35)

Always Late,

I came across your discussion on Window Condensation in the winter.  Did you find a solution?

Have a 1965 rancher on SE PA.  Had the original windows replaced about 10 years ago.  Had condensation problems.  Thought it was the windows.  Had those replaced in October, and problem now seems worse.  I guess I understand the science, but do not know where all the humidity is coming from and how to get rid of it short of using a dehumidifier.  Thanks.  BD