Too Moist? Too Dry? What's Enough Humidity


February 15, 1992|By Karol V. Menzie and Randy Johnson

It's a rare homeowner who can get through an entire winter without some sort of heating-system problem. There are plenty of things that can go wrong, and experts don't always agree on the problem, much less the solution. And sometimes, even when the heating system is working fine, the house has a problem.

That's what a Marriottsville couple wondered recently when they wrote in asking about a humidity problem.

"Help," they said, "we're confused. We recently purchased a 4-year-old home equipped with a heat pump. Despite the negative comments we have heard, we are pleased. Our bills are reasonable and our comfort level is just fine with our thermostat set at 68 degrees. We don't have a problem with static electricity or dry mucus membranes. However, we have read that we should get a system humidifier installed on our heat pump to increase our comfort level and enable us to lower our thermostat. Conversely, we were told by our home-inspection engineer that we needed vent fans in our kitchen and master bath to remove excess humidity, which would slowly destroy the structural integrity of the house. Why would you introduce humidity throughout the house and then vent it out?

"Also our house has a sub-slab ventilation system to lower its radon level. We understand operating vent fans can create a negative pressure which will draw any residual radon gas up into the upper levels of the house. Wouldn't we be better off to just allow the humidity introduced into the house from cooking and showering to remain and not install either a humidifier on the heat pump or vent fans?"

The question has several parts; so does the answer. For tips, we went to Gustin Kiffney of Energyworks, a Baltimore energy-consulting firm.

His first concern was the radon-elimination system. Radon systems usually have a device called a manometer, which indicates atmospheric pressure, he said.

"The subslab usually has a pipe that goes under the floor of the basement, which continues on up to the roof -- the whole idea is to exhaust or get rid of the radon -- and an in-line fan in that pipe that creates negative pressure in that line and supposedly sucks the radon out.

"The manometer is just a U-tube full of red liquid or mercury or whatever you want. Normally if both ends of the tube were in your room, the two levels of fluid would be equal on either side of the U," Mr. Kiffney explained. But with the radon system, one end of the U is plugged into the pipe, and the level should go up a little bit there, indicating lower pressure in the pipe, and a little suction. (Some systems may not have manometers, he said, but they should have an indicator light or buzzer to tell you the pressure's OK.)

"So whenever you look at your radon system, you're supposed to be able to look at this tube and see that the fan is working, that there is suction, or negative pressure is being generated."

"What radon installers usually do," Mr. Kiffney said, "is draw a little line on the negative end saying this is what your negative pressure ought to be. And if it goes below that, then you don't have enough negative pressure -- something's gone wrong, a bird made a nest in the end of the tube, the fan broke, you're running your Jenn-aire at full bore -- and it's creating negative pressure in the house that's more than the negative pressure in the tube."

Whatever activity is going on in the house, the homeowner should be able to check the manometer and see if the pressure is where it should be.

A well-designed radon system should be able to support the entire normal range of activities in the house without interfering with the radon system, he said.

As for adding humidity, he said, "That's rarely a good idea."

The idea of increasing "comfort levels" by increasing humidity is based on the notion that rapid evaporation of moisture from the skin makes a person feel colder; moister air will lead to slower evaporation, and more comfort.

"That may be true," Mr. Kiffney said, "but it's not significant." The difference is usually only a matter of a degree or two -- and if the homeowners are comfortable already, what's the point?

Besides being energy-users, humidifiers are rarely long-lived devices, Mr. Kiffney said, partly because they require far more maintenance than most homeowners really want to devote to them.

The third part of the question involves the wisdom of spot-venting in master bath and kitchen in view of the radon problem.

The effect of spot venting on the radon system is not predictable, Mr. Kiffney said. The only way to find out what happens is to run the vent fans while monitoring the radon system for proper pressure. Again, the radon system should be able to handle normal ventilation.

We think venting in bathrooms and kitchens (and in the laundry room, if you have one) is a good idea; in some places it's even part of the building code.

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