Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

To Humidify, or to De-humidify?

  1. May 29, 2005 #1
    I went to my local DIY store (hardware store) today and they were doing a special offer on De-humidifiers... On the same shelf, they were selling Humidifiers!!

    Which one should I buy?
    Do I want to be Humidified or Dehumidified??

    Should I buy both and let them fight it out in a sealed room??

    Which would you rather be - humidified or de-humidified? Perhaps I should start a poll? :confused:
     
  2. jcsd
  3. May 29, 2005 #2

    Evo

    User Avatar

    Staff: Mentor

    The usual needs are a humidifier in the winter to replace moisture removed by heating and dehumidifier in the summer, when humidity is more of a problem.
     
  4. May 29, 2005 #3
    So that's both then!

    Life is SO complicated sometimes....
     
  5. May 29, 2005 #4

    matthyaouw

    User Avatar
    Gold Member

    the question is- do you really need either?
    My house needs a dehumidifyer (2, actually, plus extractor fans) because we have a problem with damp and mildew. Lack of humidity never seems to be an issue for us.
     
  6. May 29, 2005 #5

    Danger

    User Avatar
    Gold Member

    Awww... that's sweet. They both have someone to play with.

    I think that the most practical way to dehumidify your house is to pump it full of liquid nitrogen. Then hit the air with a hammer and shovel it out before it thaws.
     
    Last edited: May 29, 2005
  7. May 29, 2005 #6
    I like this idea. Who would win in a fight in a sealed room, a humidifier, or a dehumidifier? You could take bets.
     
  8. May 29, 2005 #7
    lol I have both, here in Michigan, being surrounded by water, summers can be really hot and humid. I have a whole house air conditioner, but its expensive to run. So sometimes it makes it feel much cooler by just running the de-humidifier.
    :blushing: I just need to remember to empty it
     
  9. May 29, 2005 #8
    I could plumb the dehumidifier into the humidifier so that I wouldn't have to fill up or empty either. That might work.
     
  10. May 29, 2005 #9

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    We do both for our lab. We need a constant humidity of 45% (+/-5%) all year round, so we humidify during the winter (when ambient humidity at room temp can be as low as 5%) and dehumidify in the summertime (the building AC does most of the dehumidification, but we need to go just a little further to get within our allowed range).

    Normally, around 40% to 60% is considered comfortable, for human habitation (at about 20C or 70F).
     
  11. May 29, 2005 #10

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Our building (physics dept) is terribly old and has a virtually dead HVAC system. This simply does not give us the required temperatures for our cleanroom when outdoor conditions fall within a specific narrow range. Every year, for a couple of weeks we need to achieve additional cooling, beyond what the building HVAC system gives us. We do this with liquid nitrogen. We gave up on promises to fix the HVAC and designed and installed a PID controlled delivery system that pours LN into a rack of stainless steel baking trays mounted inside our supply duct. We now have beautiful temperature and humidity control, 365 days a year.
     
  12. May 29, 2005 #11

    Danger

    User Avatar
    Gold Member

    Dang, it's embarrassing when one of my jokes turns out to have a practical application. :redface:
     
  13. May 29, 2005 #12

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I'm guessing this is a problem only in the summer. Normally, a healthy air conditioner will provide outlet air at a dew point of no more than 50F (typically about 40 to 45F). This corresponds to a relative humidity value of 50% which is comfortably low. Adding in the moisture produced from human respiration and perspiration will make this number no more than 60%. If the humidity is, in fact, much higher than this, I suspect there may be a problem with your air conditioner.
     
  14. May 29, 2005 #13

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I only need a humidifier in the middle of winter. Some people prefer a dehumidifier in summer, but humidity doesn't bother me. Of course, depending on where you live, some people need a humidifier in the bedrooms and a dehumidifier in the basement.
     
  15. May 30, 2005 #14

    russ_watters

    User Avatar

    Staff: Mentor

    So, then what do you do in the spring and fall? :devil:
     
  16. May 30, 2005 #15

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Open the windows! :biggrin:
     
  17. May 30, 2005 #16
    I'd almost have to say, if you don't know which one you need, you don't need one. I live in a basement apartment, and the need for a dehumidifier is readily apparent, especially in the bathroom (no fan or window). Without the dehumidifier, it doesn't take long for mold to start growing on the ceiling. :grumpy:

    If you're really unsure and concerned about it, buy yourself a hygrometer. I picked one up for about $2 at my local Wal-Mart.
     
  18. May 30, 2005 #17

    Evo

    User Avatar

    Staff: Mentor

    Originally Posted by russ_watters
    So, then what do you do in the spring and fall?

    Yep!
     
  19. May 30, 2005 #18

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Is that even up to code? Here, building code requires all bathrooms have to have either a fan or window.
     
  20. May 31, 2005 #19
    We no longer have the need for a humidifier in the winter because we have a fish tank. This seems to add enough humidity to keep down static shocks, dry hair, sinus problems, etc, without adding a humidifier. In the summer, we use our central air, but our basement has two dehumidifers that we run all season.
     
  21. May 31, 2005 #20
    International Mechanical Code requires 20 cfm continuous or 50 cfm intermittant mechanical ventilation, or you can prove that natural ventilation can be provided by operable windows that have enough open area to ventilate the space.
     
  22. May 31, 2005 #21
    LOL. Yeah, I'm aware of the building codes, although the local ones are aren't exactly the same and subject to a bit of interpretation by a building inspector. Whenever we remodel an old house, we install a bath fan unless there's a window in the bathroom. On the other hand, when you buy a house someone else has already remodeled, it's common to find one that somebody did 'under the radar.'

    On most of the old houses we've got, the bathrooms were added on after the fact (the front/back porch was converted to a bathroom) and complied with the codes of the day, which as far as I can tell were pretty basic and just required a few things like S-traps for the sinks. I've even seen a few with old drum-traps, although I get rid of those in a hurry. As for mechanical codes, I'm not sure there even was such a thing before the advent of HVAC. We usually try and bring them up to code, but unless we're doing mechanical work such as heating and air in that house, the old work is grandfathered in.

    In the case of my particular apartment, I would have to drill a 4" hole through a half dozen ceiling/floor joists and a cinder block wall to properly vent a bath fan. Given the amount of work invovled and the potential structural weakening involved (I really hate drilling 4" holes in floor joists unless I just have to) I decided it was easier to just put a dehumidifier in there.
     
  23. May 31, 2005 #22
    Yeah, I know. I can't design them that way, but that doesn't mean they don't get built that way. :wink:
     
  24. May 31, 2005 #23

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Oh, you're living in an apt in a building you own? I thought this was a place you were renting, in which case the landlord should bring it up to code before renting it out to tenants, especially if the moisture was bothersome enough to require a dehumidifier. But if you own the place and know what you're getting into, as far as building code violations go, lack of a bathroom fan isn't high up in priority on my list of things to worry much about (I too have a bathroom where the previous owners walled over the window...I don't want to still own this house if the window ever needs replacing :eek: ...and of course didn't bother to install a fan when they did that; but I also don't use that bathroom very frequently, so am not concerned enough about moisture build-up to fix it...I've decided I'm not going to live here more than another year or so, so the upstairs bathroom isn't getting remodeled either --I was going to install fans in both rooms at once when the upstairs bathroom was gutted).
     
  25. May 31, 2005 #24
    My father owns it actually. I've got a couple of houses, but they're rented out right now. I do a little work for him now and again to cover his costs for the apartment.

    As for bringing the units fully up to code, it's usually not something that's required for rental, at least not in this area. The inspectors are generally just looking for major issues that could cause safety problems. For example, the windows in my apartment are about 5 feet above the floor. The fire inspector required the last owner to build steps underneath the windows so that a short person or a child could get out in the event of a fire. With the age of a typical house in the neighborhood, requiring every item in every house to be brought up to code would probably double the rental rates.

    In the case of my particular bathroom, the only real problem is the ceiling directly over the shower. Again, it's some 'creative' work from a previous owner. The ceiling is only 6 feet above the floor of the shower stall and rather than using something waterproof like concrete backerboard, this 'induhvidual' used regular drywall, so over the years the moisture has started to separate the paper tape from the drywall. It also tends to absorb the water rather than just letting it drip down into the shower and down the drain (thus the mold.) The dehumidifier dries out the ceiling well enough to prevent further damage from occurring. At some point though, I'll replace that ceiling with backerboard and a good vapor barrier and that should be the end of the problem.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook