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On Dripping Pipes of Summer

by: Paul Kando

It is finally summer again. You take off those old storm windows and perhaps even the new indoor window inserts you made last fall that made such a difference on cold winter days. If you followed sound advice, and removed your window screens in the fall - because they block out a lot of solar heat gain you could use to cut down on heating costs - you must now also reinstall those, freshly rinsed and dried, of course. All this likely means several trips to the basement. So, while you are down there, you remember to open the basement window for the summer to air out the moisture, right?

Wrong. If you want to air out your basement, do so on a dry and fairly cool day for a few hours by opening the basement windows, perhaps even the bulkhead, if you have one. But then close those windows and keep them closed all summer. Why? Because if you keep them open, you actually invite moisture to come in.

Remember how those cold water pipes running through the basement sweat every summer, dripping water all over the basement floor? Remember the damp, perhaps even rotting, basement ceiling joists, the sogginess of stuff stored down there? Well, chances are all that moisture came in through those open cellar windows. Here is why:

  1. Summer heat causes water to evaporate and warm air holds more of the evaporated moisture (water vapor) than cooler air. This is why we speak of relative humidity - the amount of moisture the air can hold is relative to the temperature of the air. So, when warm air cools to what is called the dew point temperature, it releases all the moisture it can no longer hold.
  2. Heat only moves in one direction, from warm to cold. When the cellar windows or the bulkhead door are open, the warm air will naturally move from the warm outdoors into the colder basement. Any cold surface there will invite all the moisture the cooling air can no longer hold to condense (i.e. settle out). The first such surface is the cold water pipe. The next might be the cool concrete or dirt floor. Any solid surface will do, as long as it is cold enough, including, alas, those wet - and perhaps rotting - ceiling joists.

In addition to the condensation problem, the relative humidity of the air in the basement will be near 100 percent. Since after any moisture the air couldn't hold will have settled out, the air will still be saturated with all of the moisture it can hold at the basement's temperature. High humidity provides ideal conditions for moisture borne allergens, such as mold and mildew, to thrive. There they will grow and accumulate all summer. Then, as soon as winter heating begins, the heated air in the house will rise (because it is less dense then cool air) and escape though holes and leaks into the attic, sucking cooler, moisture and mold-pore laden air up from the basement into the living spaces. No wonder you sneeze and have all those symptoms of the cold.

In short, the tradition to keep those cellar windows open to dry out the cellar is a source of unexpected problems. It is based on falsehood. I know, I know, your dad and your granddad before him followed that time honored advice. Still, as you can see, the advice was wrong. Luckily, at least some of us humans, unlike old dogs, have this going for us: we can learn new tricks.