Plumbing an island sink

Q We want to add a sink to our kitchen island, but we’ve been told the plumbing is tricky. How should we handle it?

C. Rayburn, via e-mail

A You’re right. Plumbing an island sink is challenging. It can’t be vented the same way as a regular kitchen sink. Here’s how it works.

Plumbing vents (a network of pipes that carry air and gas outdoors through a pipe exiting your roof) are essential to supply enough air to keep equal pressure in the plumbing system. They keep water and waste moving through the pipes at the right speed. A flow that’s too slow leaves behind debris that clogs pipes. If it’s too fast, suction siphons water from the P-trap (see photo), allowing harmful sewer gas to enter your home.

A regular kitchen sink, adjacent to a wall, has a vent hidden in the wall that connects to a vent. So it won’t plug up, the vent must rise 6 in. above the overflow level of the sink before the pipe goes horizontal. Obviously, a vent pipe in a kitchen island can’t do that.

As an alternative, most plumbers recommend a special type of vent (photo right) that loops as high as it can go inside the cabinet before heading under the floor and over to the main vent in the wall. Always get approval from your local plumbing inspector before installing this type of vent .A second cleanout may be required in the vertical wall vent pipe.

Island Vent (standard method)

An island vent rises as high as possible under an island before running to a regular vertical vent. It keeps air in the drain system and prevents siphoning of the P-trap.

TIP: If you plan to attach a garbage disposer to an island sink, replace the sanitary tee and cleanout adapter with a flat-patterned cleanout tee. That makes it easier to snake the top of the loop if it gets plugged.

A second option—one that requires no outside venting, makes installation much easier, and is either loved or hated by plumbers—is called an air admittance valve (AAV; photo, p. 8). These are not the spring-operated cheater vents used in trailers; they’re gravity-operated valves that open when water flow creates negative pressure, allowing air to enter to equalize pressure. But before you opt for this choice, you need to understand the pros and cons, as well as contact your local plumbing inspector to determine if an AAV is allowed (many local plumbing codes in the United States currently accept AAVs).

AAV Vent (alternative method)

An air admittance valve, approved for use in certain states, provides air for drainage but remains shut to sewer gases. And it eliminates the need to run a vent pipe under the floor.

If installed correctly, they can work in most single-family homes, as long as there’s one primary main vent that penetrates the roof to outside air. Drawbacks? Sometimes AAVs can’t keep up with the venting needs of high-volume (18 to 22 gpm) discharge washers and dishwashers. And AAVs have a tougher time relieving pressure in the drainage and vent system of five-story buildings and higher.

For more information on AAVs, contact the following manufacturers:

Ayrlett: (877) 338-7455, www.ayrlett.com

Magic Vent: (800) 231-3345, www.rectorseal.com

Oatey: (800) 321-9532, www.oatey.com

Studor: (800) 447-4721, www.studor.com

Why do my bulbs burn out so quickly?

Q Our porch ceiling light fixture was going through light bulbs once a week. We replaced it with a sealed fixture and bulbs lasted three weeks. Can you shed some light here? The fixture is under an eave, so it doesn’t get wet.

W. Hare, Joplin, MO

A The cause of your bulb failure could be vibration (if a door shutting shakes the wall), cheap light bulbs or excess voltage coming into your house.

If the problem is vibration, aside from trying name-brand quality bulbs, try Rough Service (RS) bulbs. RS bulbs ($2.50 each) offer greater support and bracing for the filament inside the bulb to reduce the effects of vibration and jolts.

If you suspect higher voltage could be the cause, try bulbs rated for 130 volts ($1.50). If you have slightly higher voltage entering your home—such as 125 volts instead of the normal 120 volts—it can dramatically shorten the life of a normal 120-volt bulb. A 130-volt bulb should be able to handle this excess voltage and will therefore last much longer. You can buy RS bulbs and higher voltage bulbs at home centers and hardware stores.

How often should I change my furnace filter?

Q Is fall the best time to change the filter on our forced-air furnace, and which type of filter should I buy?

G. Swartz, via e-mail

A If you’re thinking that you only have to change your filter once a year, you may well be shortening the life of your furnace. Actually, you should check your filter monthly and often change it monthly, depending on the type of filter you use. To determine if it’s too dirty, remove the filter and hold it up to the light. If you can no longer clearly see light, change the filter (see photo).

Many costly repairs can be avoided with regular filter changing. If you don’t change the filter, lack of airflow through the furnace will cause it to overheat and shut down. Similarly, a dirty filter can cause an air conditioner to shut down because the coils freeze up when airflow is inadequate. Both events stress the system.

Filters are designed to protect the blower motor from dirt. When buying filters for this task, the 50¢ glass fiber filter will do the job. But if you want to reduce airborne dust in your home, you could start with the best of the inexpensive 1-in. disposable filters—the standard pleated filter ($1.25 to $2 each). Better yet, to remove even more small particles, install an inexpensive, electrostatically charged fiber filter ($10). 3M Filtrete is one common brand (888-364-3577; www.3m.com). Just make sure to check the filter monthly and change it when it’s dirty (not just every three months as recommended).

All other options, from a 4-in. thick mechanical air filter to an electronic filter plate system, involve electrical or ductwork changes by heating/cooling contractors. They remove more particles, last longer and cost more.

Finally, whatever filter you use, make sure you reinstall it correctly, with the arrow on the filter edge pointing toward the blower motor. Putting it in backward decreases the filter’s efficiency.

Removing bathroom humidity

Q Instead of buying a bathroom exhaust fan that automatically turns on and off based on the humidity, can I simply buy a wall switch with this type of sensor?

M. Wachholz, Champlin, MN

A No, to our knowledge no one offers a humidity sensor in a bathroom-type wall switch. As you mentioned, humidity sensors are found in some top-end exhaust fans (from Broan, NuTone and Panasonic). While these humidistats can help, there are a few disadvantages. You may have to adjust the sensor during periods of high seasonal humidity, then readjust when the seasons change (and some fans cannot be adjusted). The second disadvantage is that, compared with other controls, it requires rather complicated wiring and programming.

We believe the best all-around and most cost-effective way to remove humid air is to replace your switch with a quiet, automatic timer switch. The fan goes on when you set the timer, then shuts off when the time runs out. One example is the GE 30-Minute Timer Switch we used (see photo) that converts a standard-sized wall switch into a digital timer. It’s catalog No. GE5100E3071D and costs $20 at home centers. Or visit www.gelighting.com.

Simply touch the 5-, 10-, 15- or 30-minute area of the switch to set the timer. It also lets you bypass the timer by providing a button for normal on/off switching. Granted, this solution won’t satisfy your desire for the fan to kick on automatically, but a timer switch gives you the freedom to remove humidity for up to 30 minutes after you leave the room, without the worry of forgetting to turn the fan off. A good rule of thumb, according to the Home Ventilating Institute, is to run your fan for 20 minutes following bathroom use.

Art Direction • GREGG WEIGAND

Photography • BILL ZUEHLKE

Consultants • AL HILDENBRAND, MASTER ELECTRICIAN, and CHARLIE AVOLES and LES ZELL, MASTER PLUMBERS