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Dangerously Low Humidity


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What we are really talking about is temperature compared to dew point. The dew point is that temperature at which the air would be saturated (think fog) given its current moisture content. Unless there is actually fog forming or moisture condensing on surfaces, the dew point is lower than the temperature. So if it is 20 degrees outside, the dew point is lower than that. If you then bring that air inside and raise its temperature, the dew point does not increase, at least not by much. Hence the relative humidity drops, and when it's really cold, it drops a lot.

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On 2/17/2021 at 11:33 AM, David Burgess said:

I hope people in the US are being very careful about humidity, with the unusually cold temperatures we are having. Where I live, the indoor humidity would be 3% right now (despite the outdoor humidity being 78%), if I were not adding moisture.

During most ordinary winter months, I can get by with using one steam vaporizer. Currently, I am using two, and they are running about 85% of the time to keep my shop humidity up to 40%.

Which brand of vaporizer(s) are you using at the moment?

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2 hours ago, cellopera said:

Which brand of vaporizer(s) are you using at the moment?

I'm using the Sunbeam 1388 with a separate controller, but these have recently been discontinued. A similar style is the Vicks V-150 (also around 20 bucks), but these don't vaporize water as fast as the Sunbeams did, so if you need more moisture than one will put out, you might need to use two.

https://www.target.com/p/vicks-warm-steam-vaporizer-humidifier-with-night-light-1-5gal/-/A-10403767

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5 hours ago, David Burgess said:

You've got some stuff wrong. A forced air system (in heating mode) does not remove any moisture from the inside air. In one of the less efficient forced air systems, some inside air may be used for combustion, requiring that this be replaced by outside air, but this is no different from a  hot water system, or even a fireplace or a wood burning stove.

If you still wish to claim that a forced air heating system removes more moisture from the habitated space than a hot water system, please describe the mechanism by which it does so.

OK I apologize if I have insulted anyone here based on their heating choice. I was simply stating what I thought up until today was an uncontroversial well established fact. I can walk into a house in winter and tell within 30 seconds what kind of heat they have simply by how quickly my nose dries up. Why that is? My best understanding is either because as the circulating household air is drawn into the furnace system it loses humidity, or because as it circulates through (leaky) ductwork it loses humidity to unheated spaces, or both. If you are convinced this is not the case then we are at an impasse. Naturally also some hot air heating systems work better than others, and there are as always also other factors at play. With that I must bow out.  

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17 hours ago, stringcheese said:

What we are really talking about is temperature compared to dew point. The dew point is that temperature at which the air would be saturated (think fog) given its current moisture content. Unless there is actually fog forming or moisture condensing on surfaces, the dew point is lower than the temperature. So if it is 20 degrees outside, the dew point is lower than that. If you then bring that air inside and raise its temperature, the dew point does not increase, at least not by much. Hence the relative humidity drops, and when it's really cold, it drops a lot.

I'm going to read this over and over again until I understand it! I don't know how digital hygrometers determine RH, but will the number shown be a fair representation of the actual dew point if placed indoors, or am I conflating RH and dew point... :huh:

For the time being, I've bought a couple of digital hygrometers and an ultrasonic vaporiser (~6L capacity + built-in hygrometer) and left it running 24/7 aiming for a RH of 50%.

 

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1 hour ago, milkpowder said:

I'm going to read this over and over again until I understand it! I don't know how digital hygrometers determine RH, but will the number shown be a fair representation of the actual dew point if placed indoors, or am I conflating RH and dew point... :huh:

 

Absolute humidity, (not "relative humidity") is measurement of how much water air contains, often described in terms of the water weight contained in a volume of air, such as 20 grams per cubic meter. This by itself does not describe how much water the air contains, compared to how much it can hold, which varies with temperature.

Relative humidity doesn't tell you how many grams of water are contained in a cubic meter of air, but indicates how much moisture there is, compared to how much the air could hold at a that temperature. At 100% relative humidity, the air can hold no more. At 50% relative humidity, the air is holding half as much moisture as it could be holding.

The reason we are mostly concerned with "relative humidity" in the woodworking world is that it tracks very closely with the moisture content of the wood. 50% relative humidity at 0 degrees F will produce about the the same water content in the wood as 50% relative humidity at 70 degrees F, even though the warmer air contains much more water per cubic meter.

As the moisture content of wood changes, so will the dimensions, the weight, the stiffness, the susceptibility to plastic deformation, and the susceptibility to mold, fungus and insect invasion.

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16 hours ago, _Alex said:

OK I apologize if I have insulted anyone here based on their heating choice. I was simply stating what I thought up until today was an uncontroversial well established fact. I can walk into a house in winter and tell within 30 seconds what kind of heat they have simply by how quickly my nose dries up. Why that is? My best understanding is either because as the circulating household air is drawn into the furnace system it loses humidity, or because as it circulates through (leaky) ductwork it loses humidity to unheated spaces, or both. If you are convinced this is not the case then we are at an impasse. Naturally also some hot air heating systems work better than others, and there are as always also other factors at play. With that I must bow out.  

Certainly no apology required as far as I'm concerned.  

I think there may be a difference in RH retention between radiant and forced air heating... but it does not appear that it is currently universally established (ie. how much of a difference or exactly why).  Unfortunately, most of the information available on the web seems HVAC contractor driven (claiming things like radiant heating makes it more comfortable at a lower temperature because of humidity retention... but a lower temperature in itself would increase RH...), which doesn't make the opinions wrong... but it doesn't show data to support the various positions. If there  is a study that explains the variant, I love to see it, just out of curiosity.

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I have a question about bows. I own several, and they are all at my studio, which is basically a house where I teach and work. I have no humidifier at all, I have two cellos that are in the closet and  warm, is humidity a potential danger to bows? And in the absence of a humidifier how should I protect my other cellos?

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2 hours ago, David Burgess said:

Absolute humidity, (not "relative humidity") is measurement of how much water air contains, often described in terms of the water weight contained in a volume of air, such as 20 grams per cubic meter. This by itself does not describe how much water the air contains, compared to how much it can hold, which varies with temperature.

Relative humidity doesn't tell you how many grams of water are contained in a cubic meter of air, but indicates how much moisture there is, compared to how much the air could hold at a that temperature. At 100% relative humidity, the air can hold no more. At 50% relative humidity, the air is holding half as much moisture as it could be holding.

The reason we are mostly concerned with "relative humidity" in the woodworking world is that it tracks very closely with the moisture content of the wood. 50% relative humidity at 0 degrees F will produce about the the same water content in the wood as 50% relative humidity at 70 degrees F, even though the warmer air contains much more water per cubic meter.

As the moisture content of wood changes, so will the dimensions, the weight, the stiffness, the susceptibility to plastic deformation, and the susceptibility to mold, fungus and insect invasion.

Thank you for the lesson! It's interesting that the water content in wood will be similar the same RH at varying temperatures. One would assume that because there is a higher AH t in the atmosphere at 50%RH 70°F than 50%RH 0°F that the wood would also contain more water. Is it not the case that eventually, the water content in the wood would go up if going from 50%RH 0°F to 50%RH 70°F. I am under the impression that the change in water content in the wood is the reason why instruments which are suddenly placedfrom the former to the latter atmosphere, or vice versa, would experience swelling/open seams or cracking due to the wood contracting or expanding at different rates.

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My brain is determined to be dyslexic this morning...so I'm not putting anymore time into trying to figure out various humidity designations and how it all works...

However, I continue to be amazed at how quickly the 4 litres of water from my passive humidifiers are taken up by the air in the music room...

I keep expecting it to start raining in there...

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19 minutes ago, PhilipKT said:

But that doesn’t answer my question.

I'd be skeptical of any solution other than actually raising the humidity. The ones designed for cases are OK, and I think we've all done the sponge in a jar trick, but I think the best solution is to humidify the space.

In the old days I left pans of water on the radiators, refilling them almost daily, until I wised up and went over to the junk store and bought a used humidifier, for about the price of a set of strings.

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3 hours ago, PhilipKT said:

I have a question about bows.... no humidifier at all, I have two cellos that are in the closet and  warm, is humidity a potential danger to bows? 

Potentially, at least temporarily, because even a plain plank can change shape, twist, due to dryness, perhaps recover when humidity comes back.  The vaporizers DB is talking about are great, and cheap.  I got my last one at K-Mart for $11.  They last longer than little appliances sold as humidifiers, and really pound moisture into the air compared to them.  A room hydrometer sitting on a table somewhere and you're all set

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It's not really all that simple:

What room humidifier works best?  Yes it depends, but there are pros/cons associated with any of the following:

1. Passive (which I'm trying this year, since one of my guitars decided to have issues)

2. Evaporative 

3. Cool mist

4. Warm mist

5. Ultrasonic

6. Vaporizers

Despite what the advertising for any particular type may claim, ALL of them have to be refilled regularly and kept very clean - or you'll be breathing in a bunch of bacteria and whatnot...

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Plug a warm air humidifier into a humidity controller, and the humidifier won't run all the time and you won't over-humidify the room or need to constantly change the water. 

This is what I used based on David Burgess' recommendation, and it worked great. It turned the humidifier "ON" at 40% and "OFF" at 45%.

https://www.amazon.com/WILLHI-WH1436H-Humidity-Controller-Accuracy/dp/B01IJ8YWYY/ref=sr_1_8

 

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We use evaporative humidifiers, where the water is drawn up into a wick and a fan then sends air over the wick, dispersing the moisture through the room. There is a dust filter on the back where the air enters, so it's clean air and there is a bacteriostatic treatment added to the water (in a small amount) to eliminate the bugs. We change the filters and wicks at the beginning of the heating season and again in the middle of the season as needed. We have three of them running in the main part of the shop and another one in the smaller back room. We aim for about 45 to 50% in the main shop and a bit higher in the back room, where we put all of the cracked instruments that we see this time of year before we repair them. I don't like the misting humidifiers as they tend to coat everything with a fine powder.

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5 hours ago, PhilipKT said:

I have a question about bows. I own several, and they are all at my studio, which is basically a house where I teach and work. I have no humidifier at all, I have two cellos that are in the closet and  warm, is humidity a potential danger to bows? And in the absence of a humidifier how should I protect my other cellos?

Pernambuco and the other exotic woods are generally hearty and healthy compared to spruce under greater degrees of compression or tension. Not saying that they will not be damaged by humidity, but other types of wood in dynamic roles are more likely to get damaged.  

The way the question is worded is interesting:

"... is humidity a potential danger to bows?" 

My experience has been that moisture tends to lengthen hair. Which is fine for a stored bow, but may not be playable even when the frog is screwed back to it's maximum position.

The lack of humidity will tighten most bowhair over time. With some re-hairs, where the bow is under slight tension even when fully released at the screw, there could be the danger of over tightening the bow before playing... or even in storage, the bowhair might over tighten the stick.

Some students in "auto-pilot" mode might over tighten their bows when they are taken out of their cases when the humidity is unusually. On such dry days, I do have a quick look.

As the climate changes one might pay more attention. Generally where I work the moisture is greater than 60% but due to shifts in the wind patterns, there are far more drier days in the area. I have three bows in storage where the frogs are removed over the duration of the summer as I might not play them at all during the non-academic part of the year.

 

 

 

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20 hours ago, _Alex said:

OK I apologize if I have insulted anyone here based on their heating choice. I was simply stating what I thought up until today was an uncontroversial well established fact. I can walk into a house in winter and tell within 30 seconds what kind of heat they have simply by how quickly my nose dries up. Why that is? My best understanding is either because as the circulating household air is drawn into the furnace system it loses humidity, or because as it circulates through (leaky) ductwork it loses humidity to unheated spaces, or both. If you are convinced this is not the case then we are at an impasse. Naturally also some hot air heating systems work better than others, and there are as always also other factors at play. With that I must bow out.  

I fully agree with your 30 second assessment. The hot air systems I encounter are very harsh. If you (or a violin) are near a vent your are periodically breathing air that is drier than the room average. To say nothing of accumulated dust and mold in old systems.

I'm probably not alone in finding the best systems are broad–area radiant. My partner downstairs keeps her studio air temp just above 60°F and it's very pleasant — radiant concrete floor. 

I have a hot-water baseboard which distributes mostly by convection as it is small in area and shadowed from direct radiation on my body. Short of installing broad radiators in the walls, floor or ceiling, I'm imagining that an eight foot black stovepipe hanging near the room center and heated to 80° to 90° would allow me to drop the air temperature another 5°F.

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