# Why isn't a vaporizer affecting the humidity in my room **URL:** \ **Category:** Factual Questions\ **Created:** [February 3, 2013, 7:07pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245 "2013-02-03T19:07:57Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [February 4, 2013, 5:54am UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/21 "2013-02-04T05:54:54Z")
> [@moriah](#): > > That is not how condensation at saturation takes place. If the room was so saturated that condensation was taking place on the window, and the temperature of the window was not a factor, then _ **everything in the room would be covered by condensation.** _ That’s a fact. Well, maybe not everything since different materials would respond to supersaturation in different ways with fabrics becoming damp. But, if the glass of the TV isn’t covered with condensation, but the glass of the windows is, then that is because of the colder temperature of the windows. And thus, it is _not_ a sign of 100% RH. Perhaps you don’t understand saturation in this context. Like a wash cloth that is dripping wet and won’t accept any more water—saturated----this room is saturated with water _ **vapor.** _ If you add more vapor it will condense out. It doesn’t need to be raining for the room to be saturated if we’re talking about water _ **vapor.** _ It will condense below the dew point, right? And what surface is guaranteed to be below the dew point? The windows. So we’re not talking about 100% RH (and that never came up till your post) It doesn’t need to get to 100% RH----or anywhere near it----for the room to be saturated with water vapor. And the colder it is outside, in most cases, the lower the humidity you can achieve. > [@](#): > > It _is not_. At least, not according to the OP’s hygrometer, which could possibly be not working correctly. If it is working correctly, then the humidifier is having a neglible to no effect. We don’t have enough info in this thread to make that statement. The OP didn’t state what the temp and RH% outside have been in the days he was running the vaporizer. From the things he’s shared so far, however, my educated guess is that it has added humidity to the room. He may not be happy with 25% RH, but there is possibly factors beyond his control (and knowledge) that make his desire for higher humidity unrealistic. (and his seeming suspicion of both the vaporizer and hygrometer unfounded.) IOW, it’s possible-----if not likely----that they’re working fine, as as good as the circumstances allow. > [@](#): > > And here I’m going to stop you. You don’t know what you’re talking about. Here in NJ with temperatures going below and above freezing point, the average RH here is about 55% outside (which is about 20% inside [and the comfort range for humans is the 45-55% range]). So, unless you know the OP is living in a dessert, your WAG is pretty wild. But I do think I do know what I’m talking about. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [February 4, 2013, 6:04am UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/22 "2013-02-04T06:04:09Z")
**moriah** We’re on the internet, and there are factors the OP hasn’t shared—and didn’t even know to share-----that would have influenced the diagnoses of an HVAC professional who was **on site.** With that in mind, my internet 2 cents might be wrong. But I’m sure the OP didn’t expect we’d nail this over the web. But the fact is, _I do this for a living,_ and have 20+ years experience. My intention in GQ is to offer my perspective and help, as I’m apt to do on an HVAC question. I’m not here to get into a debate over it. If the OP has any more questions, I’ll contribute to the thread. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [February 4, 2013, 2:01pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/23 "2013-02-04T14:01:49Z")
make a tent (complete or partial) over the bed with the vaporizer inside (but not near any combustibles). ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 4, 2013, 3:32pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/24 "2013-02-04T15:32:42Z")
> [@moriah](#): > > If the OP’s room couldn’t ‘hold’ any more water vapor, the OP’s hygrometer would have read 100%. > > If the OP’s room was at 100% RH, or, that very loose definition of “can’t hold any more” then when the OP’s humidifier throws a gallon more water into the air… where is it going? Relative humidity is a function of temperature. Say the room is at 75 degrees F and 35% relative humidity; if you cool that air to 46 F, it becomes saturated and starts to condense (i.e. the “dew point” of that air is 46 F). So if the room air is kept at 75 F but there’s a large surface in the room (e.g. a window) that’s at 46 F, you can’t raise the relative humidity of the room much above 35%. Any additional moisture will just condense on the window. If this is indeed what’s happening, the only way to raise the humidity of the room is to insulate the window better, e.g. replacing it with double or triple glazing, or applying insulating film. (disclaimer: I’m a scientist, not an HVAC expert.) p.s. My understanding is, this is why the air inside airplanes is so dry. If they tried to increase the humidity, it would just condense on the very cold metal skin of the plane. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 4, 2013, 3:53pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/25 "2013-02-04T15:53:42Z")
Saturation would only be at 100% relative humidity if the entire room were at uniform temperature. Given the existence of outside windows, it’s not at uniform temperature. The room contains the amount of moisture that _would_ be 100% humidity if the whole room were at the same temperature as the windows. And it’s possible that the hygrometer is good. Maybe the equilibrium humidity of the room without the vaporizer is just a little bit less than the saturation level. A small increase of humidity (too small to register as significant on the hygrometer) could cause it to reach saturation, and any further added moisture just condenses on the windows. ---
**Author:** ![moriah](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@moriah](https://boards.straightdope.com/u/moriah)\ **Post date:** [February 4, 2013, 5:58pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/26 "2013-02-04T17:58:01Z")
> [@Chronos](#): > > Saturation would only be at 100% relative humidity if the entire room were at uniform temperature. Given the existence of outside windows, it’s not at uniform temperature. The room contains the amount of moisture that _would_ be 100% humidity if the whole room were at the same temperature as the windows. You could still have 100% RH if the condensation wasn’t puddling water. If the condensation causes drops to form that flow off the window and pool, then water is taken out of the system (the room’s air) and RH drops. If the condensation isn’t puddling, then there is a dynamic equilibrium where as much water that condenses on the window is evaporating back into the air. > [@](#): > > And it’s possible that the hygrometer is good. Maybe the equilibrium humidity of the room without the vaporizer is just a little bit less than the saturation level. A small increase of humidity (too small to register as significant on the hygrometer) could cause it to reach saturation, and any further added moisture just condenses on the windows. If the hygrometer is good, and it’s reading 20%, then the room is far from saturation. Saturation happens at 100% RH. My money is on drafts. The flow of outside air into the house through nooks and cracks is what keeps the house oxygenated and makes heating, cooling, humidifying, and dehumidifying a constant chore to upkeep. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 4, 2013, 6:24pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/27 "2013-02-04T18:24:29Z")
> [@moriah](#): > > If the hygrometer is good, and it’s reading 20%, then the room is far from saturation. Saturation happens at 100% RH. You’re too fixated on the term; it doesn’t mean what you think it means, in this context. We’re not talking about the _air_ reaching saturation (i.e. 100% RH). We’re talking about the _room_ reaching saturation, which can happen when a large surface in the room reaches dew point. The _air_ may not be at 100% RH, but you can’t add any more moisture to it because any additional moisture will condense on the large cool surface (e.g. window). In a more extreme example, think about an airliner whose interior is maintained at room temperature, but the aluminum skin is exposed to the outside air which can be -40C or colder. So you can’t bring the humidity of the air anywhere close to 100% RH. If you installed a powerful humidifier on an airliner, all that moisture will simply condense on the skin and pool at the bottom of the plane _long_ before humidity reaches 100%. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [February 4, 2013, 7:21pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/28 "2013-02-04T19:21:49Z")
Oh, that kind of vaporizer. Never mind then! 😃 ---
**Author:** ![moriah](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@moriah](https://boards.straightdope.com/u/moriah)\ **Post date:** [February 4, 2013, 9:21pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/29 "2013-02-04T21:21:30Z")
> [@scr4](#): > > You’re too fixated on the term; it doesn’t mean what you think it means, in this context. > > We’re not talking about the _air_ reaching saturation (i.e. 100% RH). We’re talking about the _room_ reaching saturation, which can happen when a large surface in the room reaches dew point. The _air_ may not be at 100% RH, but you can’t add any more moisture to it because any additional moisture will condense on the large cool surface (e.g. window). So, basically, you’re talking about the cold window acting as a dehumidifier, with it taking moisture out of the air. But where is that moisture it is removing going? Dissolving through the glass? As I said above: You could still have 100% RH if the condensation wasn’t puddling water. If the condensation causes drops to form that flow off the window and pool, then water is taken out of the system (the room’s air) and RH drops. If the condensation isn’t puddling, then there is a dynamic equilibrium where as much water that condenses on the window is evaporating back into the air. And if you have a case of dynamic equilibrium and the measurement of the room is still 20% RH, then the room is not saturated. By definition of it not being 100%. Only if the condensation was being collected and removed from the system could you say that adding more water vapor will not increase RH. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 4, 2013, 9:29pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/30 "2013-02-04T21:29:19Z")
> [@moriah](#): > > So, basically, you’re talking about the cold window acting as a dehumidifier, with it taking moisture out of the air. But where is that moisture it is removing going? Being absorbed by the wood, wallpaper and/or carpet surrounding the window, most likely. (Which of course is a recipe for mold, so the OP really should address the condensation issue.) ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [February 5, 2013, 12:55am UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/31 "2013-02-05T00:55:16Z")
I’d like to make something clear for the OP. (and it may make it clearer for **moriah** ) When an HVAC person uses the term saturated (as **scr4** pointed out) they are referring to the _real life practical effect_ of adding/ or subtracting humidity. An HVAC person hearing that the windows are already sweating knows that there is already too much water vapor in the air; the homeowner has run the humidifier too much. As a result, _from a practical POV_, the room is saturated; adding more humidity is a bad thing. The OP would like 50% RH, and you could achieve that (likely with another vaporizer) but the consequence would have bad unintended consequences. In fact, you could make it rain if you wanted, right? But as it gets colder, the windows and exterior walls will get colder and mold, mildew and damage to the structure are likely. It is for this reason that the manufacturers (and I mean all of them) strongly recommend that you not add humidity till the windows sweat, and sweating windows are a clear indication that there is too much humidity given the outdoor ambient. So part of the problem is that **moriah** wants to hang the conversation on the technical definition vs a practical ‘best practices’ one. The other part, and a worse one, is the inferences she makes from that. She misunderstands how it all works, and some of the things she has said are factually incorrect, or likely incorrect. So twenty years of experience have taught me that: The OPs hygrometer is likely just fine. The OPs vaporizer is likely just fine. It’s **impossible** that _“the humidifier is having a negligible to no effect.”_, ( **moriah** ’s exact words) \*\*if the windows are sweating. \*\* The OP likely lives in Midwest/ Northeast-like winter conditions, and the cold conditions are the source of the cold windows/walls, and the resulting lowered dew point and sweating. The outdoor humidity was likely substantially lower than the 25-30% reported on the interior hygrometer, so while the OP may be dissatisfied with the 25-30% RH, _the vaporizer was likely a substantial improvement._ (keeping in mind that humidity fluctuates in the winter just like temperatures do) Adding even more humidity is a bad thing, if the windows are already heavily sweating. It may take a larger humidifier to do that, but the consequences are much worse than the negligible benefit. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [February 5, 2013, 1:41am UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/32 "2013-02-05T01:41:51Z")
some solutions: sleeping in an interior room, put a tented area over the bed, put window film (double stick tape you put on wood frame and stick a shrink film on, after applied and shrunk you don’t know it’s there) on the window. you don’t want moisture condensing on any surfaces. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 5, 2013, 1:56am UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/33 "2013-02-05T01:56:05Z")
> [@](#): > > The outdoor humidity was likely substantially lower than the 25-30% reported on the interior hygrometer, so while the OP may be dissatisfied with the 25-30% RH, the vaporizer was likely a substantial improvement. (keeping in mind that humidity fluctuates in the winter just like temperatures do) Correction: The outside air likely had significantly less moisture in it, but it may well have had a higher relative humidity. For any given amount of moisture, relative humidity varies with temperature. Take cold air outside that has a high relative humidity, and then bring it inside and heat it up, and its relative humidity will decrease, not because the moisture content has decreased, but because the capacity has increased. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [February 5, 2013, 2:10am UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/34 "2013-02-05T02:10:55Z")
> [@Chronos](#): > > Correction: The outside air likely had significantly less moisture in it, but it may well have had a higher relative humidity. For any given amount of moisture, relative humidity varies with temperature. Take cold air outside that has a high relative humidity, and then bring it inside and heat it up, and its relative humidity will decrease, not because the moisture content has decreased, but because the capacity has increased. True, I appreciate the correction. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [February 5, 2013, 2:15am UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/35 "2013-02-05T02:15:54Z")
> [@johnpost](#): > > some solutions: sleeping in an interior room, put a tented area over the bed, put window film (double stick tape you put on wood frame and stick a shrink film on, after applied and shrunk you don’t know it’s there) on the window. > > you don’t want moisture condensing on any surfaces. Good idea. Sometimes the biggest ‘problem’ is that the homeowner doesn’t understand what is achievable, or is practical. In other words, a system that is perceived to be not working is working just as it designed. As a result, sometimes no fix is needed as it is just a perception issue. In other cases, an unconventional solution will produce the desired effect. ---
**Author:** ![moriah](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@moriah](https://boards.straightdope.com/u/moriah)\ **Post date:** [February 5, 2013, 8:27am UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/36 "2013-02-05T08:27:25Z")
> [@raindog](#): > > True, I appreciate the correction. Really? It’s what I corrected you on earlier… > [@moriah](#): > > And here I’m going to stop you. You don’t know what you’re talking about. Here in NJ with temperatures going below and above freezing point, the average RH here is about 55% outside (which is about 20% inside [and the comfort range for humans is the 45-55% range]). So, unless you know the OP is living in a dessert, your WAG is pretty wild. Your response was to ask what I did for a living. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [February 5, 2013, 12:52pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/37 "2013-02-05T12:52:02Z")
> [@moriah](#): > > Really? It’s what I corrected you on earlier… > > Your response was to ask what I did for a living. I asked you because your ‘theory’ was almost certainly wrong, including the inferences you drew from it. Listen, I love GD and have spent a lot of time there. And…there is nothing wrong with people making suggestions, and even corrections. But you don’t have a firm understanding of the topic and therefore don’t really have valid basis to turn the question into a debate. Stick to topics you know something about. I’m done with this thread. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [February 5, 2013, 6:52pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/38 "2013-02-05T18:52:26Z")
The I’m the expert so listen to me tactic, eh? Meanwhile … The problem seems to be the windows. 1. Air infiltration. Cold dense air coming in and expanding (hence dry) and warm moist air leaking out. 2. The cold windows functioning as dehumidifiers, pooling the water in the window frame and on the sill. Try getting some of those shrink wrap window sealers. Your humidity will increase a bit. Until then the HVAC expert advice is correct – condensation on exterior surfaces will cause mold growth. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [February 5, 2013, 7:48pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/39 "2013-02-05T19:48:34Z")
> [@DSeid](#): > > The I’m the expert so listen to me tactic, eh? > > Meanwhile … > > The problem seems to be the windows. > > 1. Air infiltration. Cold dense air coming in and expanding (hence dry) and warm moist air leaking out. > > 2. The cold windows functioning as dehumidifiers, pooling the water in the window frame and on the sill. > > Try getting some of those shrink wrap window sealers. Your humidity will increase a bit. > > Until then the HVAC expert advice is correct – condensation on exterior surfaces will cause mold growth. Actually, yes, that is the tactic. I’ve been a lurker/ member for a decade and have 4000 posts, a great deal of them answering HVAC questions. And while I may be wrong every once in a while, in addition to a small handful of posters who have some background in HVAC here, I am for all practical purposes an expert on this MB. (and on many instances posters have directed OPs to “raindog”, who does this for a living.) And I don’t need to re-earn my bones by debating everyone who comes along with answers that are incorrect. This is a MB ferpetesake. The OP is free to choose any answer he wants and accept it as valid. If I’m having a problem with my Volvo I go to **Rick**. (and I have) I go to someone who has a level of expertise. So, yea, the answer is, “I know a little about this.” GQ can be a happy little democracy where everyone gets an equal vote. But when I have a question, I want to talk to someone who knows what they’re talking about. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [February 5, 2013, 8:43pm UTC](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245/40 "2013-02-05T20:43:10Z")
Expert opinion tends to be taken with a huge grain of salt by most here. The physicians don’t get away just saying because I said so, neither do the physicists. Maybe in an “Ask The …” thread but not otherwise. Your expert status gives you access to the knowledge and resources to prove what you say and to explain it clearly … perhaps … or it does not. If it does not then your opinion aint worth much. Sorry. [Previous page](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245.md?page=1) [Next page](https://boards.straightdope.com/t/why-isnt-a-vaporizer-affecting-the-humidity-in-my-room/649245.md?page=3)