Relative humidity vs Dew point.

I don't know if this subject has come up on the forum before because I haven't figured out how to search for old posts. Anyhow; Relative Humidity is the percentage of water vapor in the air at a given temperature while Dew Point is the pint where the air can know longer hold the amount of water vapor and begins to release some to get back to a balance. Relative humidity is just that : Relative.
While I still had a profession. The type of manufacturing I was involved at looked at moisture in the air as critical to our processes. Wander from the range and thousands of dollars of product could be useless and customer complaints would flood us.
Cigar smokers talk about relative humidity because it is easy and a cheap way to measure percentage of moisture at a given time. It is not however going to help you prevent mold, beetle infestation, cracking and all the other things that go on with your stogie related to moisture. Dewpoint is by far the better method to use when controlling moisture in your humidor or for aging cigars.
It is not as easy and instruments like a wet bulb test is not practical. Formulas for finding the dewpoint are complex and much info is needed; temp in celsius, elevation and a number of other factors because all these factors affect the amount of moisture the air in your humidor can hold.
There is a calculator I have found that you can calculate the dewpoint but is general and probably for sea level calculations. If you live in higher elevations such as Denver. Relative humidity is not the same as say Cape Cod. air thins as you climb and therefore cannot sustain the same percentages of moisture as at lower elevations.
The calculator can be found at: http://andrew.rsmas.miami.edu/bmcnoldy/Humidity.html
Lets say at 70 degrees Fahrenheit and 70% humidity the dewpoint is: 59.76 degrees F. At 68 Deg F. Dewpoint is: 57.84 deg F. I keep the house at 77 deg F. during the summer to conserve electricity. To maintain the same level of moisture in the humidor the Rel Hum should be at about 56%.
I recommend the following site which has good info on humidors and humidifcation:
http://education.vigilantinc.com/cigar/cigar-humidity.php
PS - No flames please.

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Comments

Gray4lines

I always thought that dew point was a "better indicator" of humidity, especially for weather applications and wondered about it relating to cigars as well... however, Id say rh is still a valuable tool and good enough for any cigar storage application. Why? Because the effective range in temp for cigar storage is pretty small, (lets say 65-73 for most people). Im not a weather man, but how much can rh change given such a small change in temp?

i think youre absolute correct in your point that rh can be misleading (like 40% rh at 120 degrees is terribly humid and 80% rh at colder temps really is kind of dry (at least I think that's how it goes). Certainly anecdotal evidence says many can "get it right" using rh alone.

I am interested an will use the DP calc's you posted!

kuzi16

the issue we are discussing is temperature.

dont get me wrong, RH vs dew point is a good thought pattern but in reality, RH is easy to measure.

why does the ease of measurement matter?
because the temp in most humidors hardly swings more than 10 or 15 degrees over the course of a year
with such a little swing in temp doing the crazy calculations to get to dew point makes little sense. the relative humidity isnt changing that much.
70 degrees and 60%-70% is easy to remember, easy to measure, and is practical considering the 10% span that cigars are best.

you can worry about it if you want, but years of personal experience and industry standards for generations keep me from worrying.

pilgrimtex:
I keep the house at 77 deg F. during the summer to conserve electricity. To maintain the same level of moisture in the humidor the Rel Hum should be at about 56%.

lowering the humidity wont solve the beetle issue.
beetles are temperature driven and humidity influenced.
if you want to prevent beetles you have to destroy them or not let the house over 70 degrees.

pilgrimtex

kuzi16:
the issue we are discussing is temperature.

dont get me wrong, RH vs dew point is a good thought pattern but in reality, RH is easy to measure.

why does the ease of measurement matter?
because the temp in most humidors hardly swings more than 10 or 15 degrees over the course of a year
with such a little swing in temp doing the crazy calculations to get to dew point makes little sense. the relative humidity isnt changing that much.
70 degrees and 60%-70% is easy to remember, easy to measure, and is practical considering the 10% span that cigars are best.

you can worry about it if you want, but years of personal experience and industry standards for generations keep me from worrying.
pilgrimtex:
I keep the house at 77 deg F. during the summer to conserve electricity. To maintain the same level of moisture in the humidor the Rel Hum should be at about 56%.
lowering the humidity wont solve the beetle issue.
beetles are temperature driven and humidity influenced.
if you want to prevent beetles you have to destroy them or not let the house over 70 degrees.

RH is the tool we measure. However one needs to understand the relationship to Temp and elevation etc.. Once you understand it you can set up a chart and determine the humidity that is right for your temp. Just going by humidity though and ignoring temp is not wise. I know the beetle problem begins at 70 deg f but in Texas to hold 70 in the house gets costly. I'd rather not make the environment too cozy for them with too high humidity as well as taking a chance with mold. LOL. True tobacco shops maintain very strict control. Someday I'll have an electronic system; once I build a cabinet.

Rain

pilgrimtex:
kuzi16:
the issue we are discussing is temperature.

dont get me wrong, RH vs dew point is a good thought pattern but in reality, RH is easy to measure.

why does the ease of measurement matter?
because the temp in most humidors hardly swings more than 10 or 15 degrees over the course of a year
with such a little swing in temp doing the crazy calculations to get to dew point makes little sense. the relative humidity isnt changing that much.
70 degrees and 60%-70% is easy to remember, easy to measure, and is practical considering the 10% span that cigars are best.

you can worry about it if you want, but years of personal experience and industry standards for generations keep me from worrying.
pilgrimtex:
I keep the house at 77 deg F. during the summer to conserve electricity. To maintain the same level of moisture in the humidor the Rel Hum should be at about 56%.
lowering the humidity wont solve the beetle issue.
beetles are temperature driven and humidity influenced.
if you want to prevent beetles you have to destroy them or not let the house over 70 degrees.

RH is the tool we measure. However one needs to understand the relationship to Temp and elevation etc.. Once you understand it you can set up a chart and determine the humidity that is right for your temp. Just going by humidity though and ignoring temp is not wise. I know the beetle problem begins at 70 deg f but in Texas to hold 70 in the house gets costly. I'd rather not make the environment too cozy for them with too high humidity as well as taking a chance with mold. LOL. True tobacco shops maintain very strict control. Someday I'll have an electronic system; once I build a cabinet.

Plus it would make your bar even more awesome.

kuzi16

according to the chart on the link you posted, at 60 degrees, (if the pattern continues as it has and will given it is all mathematical) your rh will have to be 100% to have your moisture in the "right spot"
the calculator you posted claims the same thing.
in layman's terms this means that it is raining in your humidor.
that is bad for your cigars.

if it is dew point we worry about (ideal being at 70/70 or in dew point terms: 59.76 degrees F), those of us living in cold states over the winter, who have to keep the house around 59 or 60* (to save money), have zero hope of maintaining cigars ever because if we have a steady dew point of 59.76, at 59 degrees f then the humidity will be 102% but if we lower our RH to "not raining" (any number less than 100%) our dew point gets too low and the cigars dry out.
(of course this is if i have a decent understanding of "dew point")

clearly there is a disconnect here because my house is about 60 degrees for about 6 months of every year, with my hygrometers reading 70%, and my cigars do not dry out, become brittle or crack as one would expect from a dry cigar- even though according to the calculator, i am about 30 points off of where i should be
...and in the summer when my house is commonly at 75 degrees and my hygrometer still reads 70% my cigars do not swell and explode on smoking or smoke more unevenly or get mold (as would be expected from an over humidified cigar) even though, according to that calculator, i am 11 points off of where i should be.
...and on days where i have my windows open for more than 24 hours and i go from 60 degrees (or lower) in the night to 75 degrees in the day with my hygrometers staying steady at 70% i do not get cigars that swell, crack, split, or generally show sign of being mistreated even though i have had, according to your calculator, a 41 point swing in what my humidity "should be" in a (relatively speaking) short amount of time
As far as dew point goes, that is 50.19 degrees F to 64.54 degrees F in a 12 hour period.

in reality, we must be looking for specific humidity (the ratio of water vapor to dry air in a particular mass without regard to temp) but it is just easier to deal with RH because thats what most people are familiar with and it just happens to line up nicely at 70/70

make sense?

madurofan

I'm going to chime in a little bit here. Although I mostly agree with Matt here. I just wanted to bring up some food for thought.

1)Relative Humidity is Relative to temp. In theory your temp should not fluctuate by much in your humidor. If you are having fluctuations in your temp by more than a couple of degrees it's not going to matter whether you are measuring in RH or DP because no humidification device is going to be able smooth it out. I understand it's relative to altitude as well but if the altitude of your humidor is changing there are major problems. And lets not get into your travel box. There is no way to maintain a travel box if you're flying etc.

2)We all have ways that we have determined what RH is best for our cigars. If you choose to use dew point great. You should know your altitude and roughly the temp your house will be per season. If you choose to calculate the dewpoint at your house when your AC is set at 76 and it determines that your humidity should be 60% to hit the dew point you like go for it. As log as you don't have mold or beetles and your cigars are smoking to your liking it really doesn't matter.

My point was that it really doesn't matter what you what to use as your measuring tool the ultimate goal is the same. No mold or beetles and your cigars smoking the way YOU like.

A few things to remember when we all get a little obsessed with the temp/RH/DP of cigars. Cigars are not humidifed nor climate controlled during the shipping process. Cigars have been stored and enjoyed LONG before there was a way to measure RH. You can look and feel if a cigar is being stored properly. No matter what your fancy gauges say if it doesn't feel, look or smoke right it doesn't matter.

Those of you who have been, I understand a vast majority of aging rooms in latin america aren't even climate controlled. True?

pilgrimtex

I love this. Puffing 101. Great comments. Thats what a post is for. Yes. a humidor should be at what temp you want and what rh you want. I started this for those who think a certain RH should be the same no matter what the temp. This is false. warm air holds more water vapor. cool air is more dense and cannot hold as much. thats when you have to worry about the rain. A cigar absorbs available moisture that is why you want to maintain a sweet spot of available moisture. No. air can hold 100% RH except maybe in DuBahi. Remember the bench is 70 rh at 70 deg f. the hygrometer will change reading even if the moisture remains the same because it is "RELATIVE" to that temp. Dew point is not a %. RH is what we measure because the instruments we use fit in a humidor and are cheap. If you want to accurately control it get an electronic humidification unit if your box is big enough. Again thanks for the comments and keep em comin.

MVW67

I thought relative humidity was sweat from Kin folk having S E X?? LOL

jgibv

MVW67:
I thought relative humidity was sweat from Kin folk having S E X?? LOL

HAHAHAH!!! ZING!!!
Good one, Mike.

Pilgrimtex, interesting thoughts and discussion you spurred here ....
But this is way over my head, getting too complicated for me ;-)

I like what madurofan said, I subscribe to his philosophy:

madurofan:
the ultimate goal is the same. No mold or beetles and your cigars smoking the way YOU like.

You can look and feel if a cigar is being stored properly. No matter what your fancy gauges say if it doesn't feel, look or smoke right it doesn't matter.

pilgrimtex

Being over innebriaded by my last review pardon my spellin. Just remember the cooler than 70 deg f the higher the % humidity. The higher the the temp the lower the rh. Moisture is moisture (dew pint) did I say pint? lol. the lower the temp the higher the rh. see
http://education.vigilantinc.com/cigar/cigar-humidity.php
Not bad for too much spanish brandy during a review Huh?

Cigary

My head hurts from all of this science...I just know that I keep my temps at 72 in the house and my humis at 65% and it's all good and they smoke great and if smoking cigars ever gets to a point where I need a degree in meteorology to understand how to keep care of them...I'll probably quit.....NOT!

pilgrimtex

Cigary. Your in the sweet spot at 72 so no worries there. Thats all you got to worry about.
the 70 70 rule put dewpoint at 59.76 deg f.
with your humidor at 72 and 65 the dewpoint is 59.58. Perfect.

johnbharle

Reading through this thread, it occurs to me that I may be one of the few people who live in Texas who do not have AC. Therefore, my home temperature fluctuates widely during the year. I have been concerned for some time that 70% RH is rarely the right amount of moisture for my cigars. But what is? I like the idea that I can have a constant dewpoint in my humidor. Now I know that with a DP of 60, my RH only needs to be at 30% in the summer to keep my cigars humidified (and btw, my RH is often >30% near the Gulf Coast in summer). I think I'll have to draw up a seasonal chart that allows for varying RH dependent on ambient temperature. Thanks, guys!

Vividone

Very intresting thread. I found this calculator http://dpcalc.org/ It seems using the 70/70 rule for long term storage could put your collection at risk for mold using the above calculator.

MIGS_INC

Doing some research on relative humidity and found this thread. I have a question perhaps you can answer.

Using your calculator, if I assume that I want my walk-in humidor at 70/70 but have no idea what dewpoint that represents, the dewpoint calculates at 59.77.

That said, assuming I keep my temperature at or below 72 degrees to discourage tobacco beetles/worms, do I then always set the humidity so that the dewpoint calculates to 59.77?

We are close to sea level at my location, or at least close enough so that I am not particularly concerned with deviations due to altitude.

Gray4lines

MIGS_INC:
Doing some research on relative humidity and found this thread. I have a question perhaps you can answer. Using your calculator, if I assume that I want my walk-in humidor at 70/70 but have no idea what dewpoint that represents, the dewpoint calculates at 59.77. That said, assuming I keep my temperature at or below 72 degrees to discourage tobacco beetles/worms, do I then always set the humidity so that the dewpoint calculates to 59.77? We are close to sea level at my location, or at least close enough so that I am not particularly concerned with deviations due to altitude.

I think that is correct... dew point is an absolute measure of humidity in the air, and so if you want to benchmark the 70/70 rh rule in absolute terms, then that dew point is what you want.

I think that practically no one gives a crap about dew point because the normal range of temps that you should probably keep cigars in is relatively narrow (60-low 70's) so how much will the dew point swing given that say, your rh is 68% constantly, but temp swings by 5 degrees each way? Probably not enough to worry about maintaining a constant dew point reading. It's almost too exact for cigar storage.

Lee.mcglynn

Sorry I'm late in this one been really busy!! Dew point and rh play hand in hand but few point wouldn't be a great idea to go and measure with. Kuzi is pretty much correct...dew point is where the temp drops so much and the molecules get smaller to produce moister. To produce moister there has to be 101% humidity since the molecules can not hold anymore and needs to get rid of the rest. Even if it's 20 degrees out with very low humidity if you take something ultra cold it will produce sweat like having a cold beer on a hot day. It might not sweat but you will see ice form on the outside of the container. That is the dew point...rh is just how much moister is in the molecules at what ever temp you choose