Opened Window Can End Fireplace Problem

QUESTION: I recently moved into a brand-new condominium that has a factory-built fireplace. Every time I use the fireplace, smoke fills the room rather than flowing up the chimney. Once the fire gets going, the chimney draws properly and pulls up the smoke. I don’t understand why there’s a problem. Can you help?

ANSWER: The problem is caused by a negative-pressure condition, also called depressurization, that exists in your house. This is a fairly common phenomenon in new construction, as opposed to houses built 20 years ago. To conserve energy, new homes are better weatherstripped and caulked, and are tighter than older homes.

All homes have a ventilation rate. That is the number of times the enclosed air volume changes in an hour. Air enters and leaves the house through various windows, doors and minute gaps. The typical house built 20 to 30 years ago had an average rate of 0.4 to 1 air changes per hour. Many new houses have an average rate of 0.1.

Depressurization results when more air in the house exhausts through fans and vents to the outside than flows in. The greater the exhaust and the tighter the building, the greater the depressurization.

Also, because warm indoor air is lighter than the colder outside air, it tends to leak into the attic through an access door or a ceiling hatch, and then flows to the outside through vents.

When the damper is opened, there is generally a rush of incoming air. In some cases, the rush of air is so intense it blows ashes into the room. To eliminate this, you must equalize the air pressure between indoors and out. Do this by cracking a door or window, preferably on the side of the house on which the wind is blowing. If you open a door or window on the opposite side, more air will be drawn out of the house creating an even greater negative pressure.

Try Vinegar to Clean Humidifier Sediment

Q: My hot-air furnace system is equipped with a power humidifier. The water in our area is hard and my system incorporates no water softener. The plastic basin and carousel of the humidifier must be cleaned regularly. The problem is a hard sediment forms on the basin and carousel and is extremely difficult to remove. Do you have any suggestions to make removing the sediment easier?

A: The hardened sediment that forms on the basin, carousel and flat assembly in your humidifier can be softened by soaking these parts in a solution of 50% white vinegar and warm water for about half an hour. The sediment can then be removed easily and the items cleaned. Rinse each component thoroughly and wipe it dry before putting the humidifier back together. If you don’t, the circulating air will pick up a vinegar odor for a while.

Dirt Basement Cause of Excess Moisture

Q: We had a new church built two years ago, and we still don’t have a concrete basement floor in it. The basement walls are always damp. Sometimes there are beads of water and mildew on them. There is also a real musty smell at times. I don’t think we have water coming in from the outside. I think we have a serious sweating problem. What do you think?

A: It sounds as if a lot of moisture is entering the basement from the dirt floor. If your church cannot afford to cover the dirt floor with a concrete slab, then it should at least cover the floor with 6-mil. polyethylene sheets.

Even when the dirt floor feels dry to the touch, a considerable amount of water still evaporates into the atmosphere of the basement because of the capillary rise of ground moisture.

According to the Small Homes Council at the University of Illinois, the soil under a 1,000-square-foot house can release as much as 18 gallons of water per day through evaporation.

Even with a concrete slab or vapor barrier covering the floor area, it may be necessary to use a dehumidifier to help control the amount of moisture.

Driveways Seldom Require Sealant

Q: I have a concrete driveway and I’m confused as to whether I need to use a sealer. I’ve heard both pro and con on this subject. What’s your opinion?

A: Driveway sealants are a controversial topic in many areas of the country, primarily because they are often used by traveling bunco artists to bilk unsuspecting homeowners out of thousands of dollars. In many cases, a sealer simply isn’t needed, no matter how clever or persuasive the sales pitch.

But mass hysteria aside, driveway sealants do serve a purpose in some situations. They are often required in colder states when new concrete is poured in late autumn. In this instance, a sealant keeps water from entering the slab and popping the surface with the first deep freeze.

Ironically, the more years a driveway goes without a sealant, the less it is likely to need one. the reason is that normal surface grime from dirt, car tires, and, yes, oil spills help seal the concrete. If yours is a relatively new drive, or if you’ve noticed unusual surface degradation, then a sealant is probably in order. This is especially true if your drive has a rough surface that has been finished with a broom.

For further information on any home problem, write to Popular Mechanics, Readers Service Bureau, 224 West 57th St., New York, N.Y. 10019.