Home & Garden

Mr. and Mrs. American Home Buyer, are you suffering from Stinky House Syndrome? Do strangers cover their noses and flee your dwelling soon after entering? Do relatives plan family gatherings at the homes of family members who are less scintillating than you? Are you engaging in microbial experiments without possession of the pertinent advanced degree? Does your house smell bad? If you answered yes to any of the above, you may be a candidate for dehumidifier ownership. 

As property values and rents increase, more and more people find themselves living in or using basements or backyard sheds that do not provide adequate protection against damp conditions. Even just a damp basement below your living space can subject you to elevated humidity levels that can make your entire home feel clammy and cold. This is a complex area of home care about which a great deal may be said. But let’s just cut to the chase: There is a formidable tool in the war on mold, and that’s our friend the dehumidifier. 

A dehumidifier is essentially an air conditioner—with a few notable differences. The technology that’s used to chill air in your refrigerator or air conditioner chills a set of coils and then pumps the waste heat to another set of coils for discharge. In the case of an A/C, those heat-discharging coils are on the outside: If you put your hand over them, you can feel the heat. Since moisture tends to condense on a cold surface—just as it does on your windows when you have the heat turned on—the cold coils also gather moisture from the air. 

When a dehumidifier condenses moisture in the atmosphere on those cold coils, it then allows it to drip into a pan. Rather than being placed on the outside, the humidifier’s cold coils are placed just past the chilling and dripping business in the system. They re-warm the air before releasing it into the room. This way, a humidifier is able to remove the moisture without cooling the room. Simply running an air conditioner will cool a room, but it is less efficient at removing moisture since it is not designed to provide this as its sole function. 

Now, what to do with all that gathered water? First keep in mind that the water gathered from a cold system like this isn’t safe to drink, since it is likely to contain fungal matter and dust. So it’s best to simply discharge it down a drain or out to the garden. Small, inexpensive dehumidifiers fill a small trough or tray which must be taken out and emptied from time to time, but larger ones are provided with drain pipes and can be set up to run with almost no maintenance for very long periods. Dehumidifiers are rated in terms of “pints per day”: Small models are less than 10 PPD and large ones can be over 40 PPD. You can expect the larger ones to cost well over $1,000, but they may be well worth it if you’re experiencing real distress. 

Every year I meet a few people who have a bad situation that calls out for a dehumidifier. One couple that I met last year had a tenant living in a basement apartment. Part of the tenant’s space was getting wet from a leak and featured a lovely zoological menagerie of fungi and protists (part of the mildew family). Everybody gets freaked when this is happening and all sorts of allegations of devil worship and bad genetics get hurled about, but the simple truth is that it’s just nature doing what it always does when some basic requirements are met. Nature loves growing stuff. Fungi love moisture.  

They also need oxygen and food, but those are available at everybody’s house. I haven’t seen any houses that don’t have nice sources of sugar and oxygen. A damp 2 x 4 will work nicely, thank you very much, but paper-surfaced sheetrock will work even better. We line the inside of our houses with paper, so it should be no shock when stuff starts growing on the surface. (We really ought to quit this odd habit and it is happening slowly. Alternatives to paper surface gypsum drywall have been around for some time and, in these litigious times, they’re really surging. I suspect that we won’t be able to find the paper type in another 10 years—but I digress.) 

So we have food and air, and only need water. How much water do we need to grow mold and/or mildew? The answer varies with the organism, but it’s about 70 percent to 100 percent humidity, although most growth occurs when humidity is above 85 percent. Few of these things grow below 60 percent. Basement walls often are damp enough to easily meet the requirement. When moisture is present on the surfaces it evaporates and becomes part of the atmosphere. If there is enough of this, the entire house can achieve levels where fungi begin to propagate. While rare, it is not unusual to have portions of basement, window sills, closets and spots on ceilings where little farms are a-growin’. 

Although it may seem almost too easy to find plausible, the simple deprivation of an adequate level of moisture is all that is needed to prevent fungi from growing. They just stop growing when things dry out. True, the dead spores remain and can affect the immune systems of some allergic persons, but for the most part, when things dry out, the ill effects vanish. It is wise to clean the surfaces and possibly to replace damaged or deeply infested materials such as sheetrock if these have become filled or covered with culture. (Ah, culture. Doesn’t all the Bay Area have that problem?) Once the level of required dampness is gone, there just won’t be more growth. If you want to clean and kill mold spores, a dilution of bleach works nicely. One quarter cup of bleach in a gallon of warm water is what is generally recommended and is quite deadly to most fungus. 

There are many things that one can do to prevent future mold infestation, including creating proper drainage, venting the spaces below the house, and using plastic barriers and sealants. For situations that are currently unmanageable, a dehumidifier is a quick, simple and relatively inexpensive fix. Downside? They use electricity. Like their cousins, the air conditioners, dehumidifiers use a fair amount of electricity but given the important job they do, it’s worth it. If you’re thinking of getting one, especially a “whole crawlspace” or “whole house” model, check out the energystar.gov website. You can get a rebate for making the right choice and you can help to control your electric bill. I would make sure I bought enough but not too much capacity so as to control the energy cost. Better models have humidistatic controls that allow you to set the percentage of moisture you like. Don’t set them too low. It’s not comfortable and will only cost you more money. 

The use of a dehumidifier can be a lifesaver. It may save your hacking lungs, the frame of your lovely old Victorian, or the precious relationship you have with the nice young man who lives down in the basement. 

ASK MATT 

Got a question about home repairs and inspections? Send them to Matt Cantor at mgcantor@pacbell.net.