I have a question I hope 1 of you may be able to help me with.
I have an Aprilaire Automatic Humidifier (Model 700) on each of my 2 furnaces.
I’m really trying to tweak my settings on dial, but I am getting to different pieces of information about what indoor RH should actually be set at.
A lot of websites talk about keeping indoor RH in winter between 35-45%.
Aprilaire has a guide that shows the colder outside, the lower your indoor RH should be.
Their recommendations are as follows, but let me ask my question now. Here in Chicago, it’s been very cold with temps in the below 0. Should I follow Aprilaire’s recommendations or should I keep my humidity at 35% minimum?
I have to keep my dial on 3 for the house to automatically do what their recommendations is. They say keep it on 5, but way to muggy if I do that. It takes a setting of 4 to keep it at 35% minimum when it gets real cold outside.
Also, who makes a pretty accurate hygrometer for the money? MFG and model number appreciated if you have one you like a lot.
I have a $8 one I bought at Wal-Mart, but I don’t trust it.
Thanks in advance.
+40°F 45%
+30°F 40%
+20°F 35%
+10°F 30%
0°F 25%
–10°F 20%
–20°F 15%
Edited 1/20/2009 12:02 pm by CoreyIL
Edited 1/20/2009 12:06 pm by CoreyIL
Edited 1/20/2009 12:06 pm by CoreyIL
Replies
rule of thumb setting...
when the RH just shows as condensation on the windows back down the setting a couple of points...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Forget the primal scream, just ROAR!!!
Someone will no doubt appear shortly to contradict me, but the chart you have is a reasonable one for a home of average construction, and you should follow it, more or less, at least until you develop a "feel" for the situation. (In my opinion 45% is a bit too high, and you should maybe knock 5% off the numbers shown.) In newer homes, and especially those built really "tight", with high-efficiency windows, you do not need to adjust down the humidity quite as much, but in those homes you generally don't need a humidifier either.
The more general rule is to turn down the humidity so that you get no condensation on windows above about 15-20F and relatively limited amounts (in the form of frost) below that. If you have windows of different qualities or vintages in the house you may notice that some get condensation worse than others -- kinda strive for an "average" between them. (It should be noted that you need to adjust down the humidity not just to keep the windows frost-free, but because excess humidity can cause condensation inside the walls. But the windows serve as a "canary in a coal mine" to let you know when humidity may be getting too high for the walls, so adjusting based on window condition is usually a satisfactory way to go.)
The Aprilaire electronic humidistat includes wiring and probe for an outside thermometer, to make the unit relatively self-adjusting. (It sounds like you have this unit.) You still need to turn down the humidistat sometimes, though, when you're anticipating a cold wave, since the humidistat obviously doesn't read weather forecasts.
We keep our Aprilaire humidistat (with the above feature) set at 3 during milder weather and turn it down to 2 when temps drop below zero. And we turn it off temporarily when a sudden temperature drop is anticipated. This seems to work for us.
If you're shooting sparks walking around on the rugs, increase humidity - if you're seeing some condensation on the coldest windows, cut it back!
"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."
Howard Thurman
More about the way your home is built would be helpful..
Is it traditional stick framed? super insulated with SIP's or ICF's ? How thick are the wall studs and how thick is the attic insulation?
Is there a vapor barrier?
How many people and who takes showers when?
A few houseplants? a lot of house plants?
Here's why all that information is helpful.
If you have a lot of people and they all take showers early in the morning whatever you set the humidity at it will be overwhelmed.. causing moisture issues..
Then later at night cooking can add a lot of moisture into the air..
Plants help with evening moisture fluctuations a bit but add their own moisture levels..
The vapor barrier issue is critical because if your insulation should get damp it's R value drops dramatically (unless it's foam)
Traditional stick framing provides a narrow window between too much moisture and too dry..
etc..
As you can see no one number is correct for everyplace..
But if he has a humidistat, won't his humidifier be off any time the lifestyle is pumping out moisture? If there is excess humidity at this point, it won't be the problem of the humidifier, right? Just need to ventilate (i.e. exhaust) a little bit more.
Once too much moisture is pumped into the air it takes a while to return to lower levels. it's not like an on-off switch..
True. I can raise the humidity in our house by 10 points in 6 hours or less, but it would take 2-3 days for it to drop 10 points, in our somewhat tightened mid-70s frame home. This is why you have to keep a bit of an eye on the weather forecast.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
OK. I understand what you are saying. Thanks. I'd just put in a 2,000 cfm exhaust fan ... and an "on/off" switch ... :) just kidding!! It gets so serious in here sometimes ... doesn't it? Maybe this should be lighten up day? A Breaktime holiday.
OK ... enough of my dry humor ...
I thot this thread was for wet humour;)
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Wet dreams and dry humor.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
He, Piffin ... THAT was actually funny ... I missed my own pun. I'm a little slow ... but as my mom always said ... I may be dumb ... but I'm not stupid!!
The vapor barrier issue is critical because if your insulation should get damp it's R value drops dramatically (unless it's foam)
All insulations are vapor permeable. Closed-cell urethane has a perm of about 1.1 - 1.4. Semi-close cell is 6, and open-cell is 16. Moisture adsorption will increae the conductivity of any insulation.
Traditional stick framing provides a narrow window between too much moisture and too dry..
There is nothing about stick framing which makes it different from any thermal envelope in high moisture conditions, except that it has a much higher moisture-storage capacity and will moderate a short-term increase in humidity as foam will not. Mold will grow on any surface, whether it's a food source or not.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Riversong,
You wrote, "All insulations are vapor permeable." Well, kind of. Two and a half inches of closed-cell SPF has a permeance of 0.8 perm — that's quite low. And 1 inch of foil-faced polyisocyanurate has a permeance of 0.05 perm — as close as most of us will ever get to a vapor barrier. (Of course, if you buy unfaced polyiso, the permeance is significantly higher.)
A lot of websites talk about keeping indoor RH in winter between 35-45%.
The human body prefers humidity between 30% and 70%. A cold climate house generally prefers between 20% and 40%. So the best compromise for a healthy house and healthy people is 30% to 40%. If there is considerable condensation on windows on cold nights, then you could tweak it down to 25%, but any lower and you're likely to contribute to respiratory and mucus membrane problems, and increase the prevalence of bacteria and viruses.
The Sahara is 25% RH. Death Valley s 23%. That's not the climate you want to live in.
Solar & Super-Insulated Healthy Homes
You seem to get a great deal of your misinformation via Google, and while I do not consider this a credible source, you do, and your best source of technical data, Wiki disagrees with this so very wrong statement, "The Sahara is 25% RH."
http://wiki.answers.com/Q/What_is_the_average_humidity_in_the_Sahara_desert
The statement is off by a factor of 5.
If you are willing to trylearning, you can do so. Think about the statement. 25% rh in the dryest desert on the planet? Not realistic and not true except in extreme cases.