Clothes Dryer Installation, Wiring, Venting and Troubleshooting Q&A

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Dear NH,

I am looking for some information about clothes dryer venting installation. I live in Vermont and currently vent my clothes dryer into the basement via flexible hose. The reason for this is my house is low to the ground and the dryer/washer (combination unit) is located close to a walkway outside, where an outside vent cover would be unattractive.

This causes a smell at times in the basement due to the moisture content. To run it to the other side of house would require a run over 25 feet. My house is single story and I was wondering if there is a type of vent that could go up to the roof and outside.


Adding any moisture at all to a basement is a bad plan. Basments usually don't need any help being damp and smelly!

If your dryer is powered by natural gas or propane, it is dangerous to vent to the inside! The exhaust gas is blown out with the heated air, thus poisoning your basement with various toxic gasses such as carbon monoxide, a known killer!

Sure... you can go through the roof provided you have a good location to run the pipe up, such as inside a closet. You can also build a wooden or drywall shaft to enclose the ducting.

Pick the type of duct most suited to your job, but do not use flexible plastic duct... it is no longer code-approved for clothes dryers. There is rigid stainless steel ducting, and a few types of more flexible aluminum ducting. Always choose the ducting that is the smoothest for the vagaries of the particular installation. For example long straight runs should always use a rigid ducting, while unusual bends or tight installation conditions may require a flexible duct.

There is a special roof cap designed for 4" dryer vent hose that is suitable for your job. You can get it at a home store, lumberyard, or some hardware stores.

A twenty-five foot run is considered too long by all the manufacturers, and I believe it will probably void your dryer warranty. If you find you have no alternative and must use this long run, you should 1) use a rigid ducting to reduce resistance in the duct to a minimum and 2) check the pipe for accumulations of lint at least a few times a year.

The problem with the long runs of duct is if the clothes dryer does not have enough reserve fan power to blow the air through the duct, your clothes will take longer to dry, shortening the life of the clothes dryer due to longer cycles and higher internal temperatures.

In closing (and being ever practical), have you considered that a 16 (?) foot vertical vent may not really be an advantage for you over a 25 foot horizontal run... it may even be worse! After all, air has weight, right? It will resist the dryer fan's efforts to blow out the hot air.

Dear NH,

I am installing a gas clothes dryer and associated vent duct. The standard is 4 inch metal rigid duct, but I already have a large amount of 6 inch metal duct in my possession. I will need to run approx. 8 feet of 4 inch duct from the dryer at a 45 degree upward angle. At that point I plan to connect the 4 inch duct to my 6 inch rigid duct that will run horizontally for 18 feet to the outside of the home. The table in the instruction booklet allows for a max. of 44 feet of 4 inch rigid metal duct with two 90 degree turns. My install will have 2 45 degree turns and a 6 foot vertical climb.

Will there be a problem with using 6 inch rigid metal duct instead of 4 inch duct? Will using the larger duct size increase or decrease the maximum length of duct that can be used?

JB from San Francisco, CA


There's good news and bad news. First, the good news.

Increasing the duct size will not negatively affect clothes dryer performance. Actually, as vent pipe size is increased, back pressure is decreased, resulting in better exhaust and quicker drying. The overall effect will probably be a more efficient dryer.

Now, the bad news. Using an oversized vent pipe can have negative effects, too. Your clothes dryer is designed to exhaust at a rate that minimizes the amount of lint that will settle within the vent. Increasing the size of the vent pipe decreases the speed of the exhaust, hence increasing possible lint accumulation. Over time, lint can obstruct the vent enough to cause clothes dryer overheating and possibly cause a fire!

So, you can use the larger diameter vent pipe but be sure to check it at least annually for lint accumulation and clean it as necessary.

There is another issue. If your ducting travels through unheated space, you may have to take additional steps to deal with condensation caused by the hot moist dryer exhaust meeting cold metal ducting. Under some conditions, condensation can be enough to cause water damage if it were to leak from the ducting back into your living space.

Compensate for this if possible by sloping the ducts down towards the outside so the condensed water, if any, can drip outside and not collect in the duct. You can also wrap the ducts in insulation, which would minimize condensation by allowing them to more effectively hold the heat. Also, always run the dryer long enough so that the last few minutes push only hot dry air into the duct. This will help to clear out any remaining moisture.

Dear NH,

We live in a four-story condo. All the clothes dryer vent hose is flexible plastic. It runs horizontally and is about 20 feet in length. The outside vent is a three flap louvered design. The problem is that the vents are plugging and in some cases filling with lint. What do we need to do? By the way, the piping is not accessible.


Dear R,

Twenty feet is a not-uncommon length but far beyond the manufacturer's recommended length for any dryer I have seen. This long distance promotes the accumulation of lint, since it will settle onto the sides of the pipe long before the air flow reaches the outside. Eventually, enough lint will accumulate so that it will begin to break off in pieces from the lining of the hose and appear in chunks at the outside vent cover.

The standard technique for cleaning a lint-filled but inaccessible dryer vent hose is to blow it out with a powerful stream of air from a source of high volume air. No… bringing in a gabby neighbor is not enough… I mean REAL force! Unplug the dryer and move it out of the way and disconnect the vent hose from the dryer. Using a small hand-held electric leaf blower (buy or rent), insert the business end in the hose and turn on the blower. Wrapping the connection of the leaf blower and the hose with a towel will help make a better seal and force more air into the hose.

Careful with that electric blower! If you allow it to run it too long under stress caused by the resistance within the dryer vent hose, it may overheat. This risk increases if the outside vent flapper becomes clogged as your are working! Also be sure that the blower's air intake doesn't become blocked by the towel or any other material. Be aware that some of these leaf blowers have their intake on the bottom and when placed on the floor may become restricted. And please don't use a gasoline blower in the home under any circumstances!

Properly done, this procedure will force any loose material to exit the outside vent. I suspect that your vent hose is loaded with lint and the louvers will become blocked quickly during the cleaning process. Now, the ideal situation is to REMOVE the louvered vent BEFORE you blow. Unfortunately, most concealed installations don't allow you to do that without cutting an access hole in a wall or ceiling to get behind the vent cover. The solution is to select a brave and courageous partner… wearing appropriately grungy clothing and eye protection… to clear the vent with a pencil or other blunt instrument… carefully… while you blow! (Your buddy could puncture that old plastic vent hose with an inappropriate jab!)

A word to the wise… make sure your trusty assistant isn't standing in line with the vent when you FIRST turn on the blower or she may get a face full of old stale lint. Yechh!

Dear NH,

We live in a second floor condo where the condo association, in it's infinite wisdom, has prohibited us from screening the dryer vent!! We discovered a resourceful bird who ,with his beak, opened the cover and proceeded to enter and build a nest. It's a pain to snake a wire with rags tied to it to clean this vent. Is there anything we can do to prevent this bird from using our vent as a home? Thanks in advance for any and all help.

BF, Chalfont, PA


You're right. The easiest way to keep a bird out of an existing dryer vent is to install some light-weight chicken wire over the vent cover opening. Creative bending and attaching it to the house and/or vent with screws or roofing nails can make it an effective and not too unattractive solution. This wire could also be pushed inside of the vent cover, just behind the flap, to discourage the bird's enthusiasm. This may or may not work with the vent type you have.

There are, of course, alternative vent designs. I have also seen some dryer vents that use small moveable louvers rather than a large flap as you have. These can't be entered by birds because openings are too small. There is also another type that exits the house and turns vertically. It employs a moveable valve that rises under the pressure of the dryer exhaust, thus being sealed by gravity. I have seen this type in some home product mail order catalogs, though I can't find it among the ones I have right now.

Before you make any alterations, make sure the hose is thoroughly clean of bird's nest debris. Even a small blockage will collect lint and eventually seal the hose tight!

Of course, you would need condo association approval. Which leads us back to the underlying question... the seeming irrationality of their decision. In my experience, wire covers over dryer vents need maintenance on a regular basis or they will become blocked up with lint. This can in turn lead to the same situation as the bird could cause... an overheated, inefficient dryer and a fire hazard!

Write them a letter informing them that unless they allow you to cover or replace the vent, you will in future send them a bill for the cost of cleaning the vent. This should wake them up. You can even mention that you will have your lawyer cut them a letter informing them of the responsibility they have accepted by not letting you repair the problem.

To my understanding, if the condo association controls the outside of the building and disapproves of changes that will prevent danger or damage (as I mentioned a blocked vent can cause a clothes dryer to overheat and is a definite fire hazard) then they must accept financial responsibility for their decision.

If the bird making a nest is not an act of God... what is?


Dear NH,

Our clothes dryer has not been drying clothes as effectively as it once did. It is about six years old. I read your tip about making sure the exhaust vent is clear. I took apart the front of the drier and vacuumed out the lint trap area. I also took off the hose from the back of the drier. I noticed that there was a cup of water in the vent hose. Is this normal? I also used a leaf blower to blow through the vent. A helper noticed that the flap would open completely, indicating to me that the vent was not obstructed. Is there anything else I can try?

JH from Twinsburg, OH


Water collecting in a dryer vent hose is normal and significant amounts of water can accumulate over time. In one house, I found nearly a gallon of water accumulating in a vent hose which ran through and attic. The hose had settled into the spaces between the floor joists giving the water a great spot to collect! This problem is greatest when lengths of hose pass through an unheated area. The water is produced, of course, by the condensation of the warm, moist dryer exhaust air within the hose when it enters the cooler attic.

If you are absolutely sure the vent hose is unobstructed, then your problem may be internal to the dryer, and need repair. Unfortunately, we don't carry appliance parts or handle appliance repair issues here.

You didn't mention whether you tried to dry a batch of clothes with the vent disconnected, or connected to a length of hose running out of a window... as a "control" test of the dryer. This would eliminate the vent hose from consideration immediately! (And would be the "message" that it's time to call in an appliance repair company)

If the clothes dry with the hose disconnected, it means that the hose does have a restriction. I had a similar situation with a blocked vent that "appeared" to be clear when using a high power blower. Upon examination, I found a bird's nest in the hose! The nest moved enough for the blower to open the vent flap but, since a clothes dryer does not produce as much force, flow was restricted enough to prevent proper drying!

Dear NH,

My son got a used dryer and the cord (pigtail) that came with it did not fit his receptacle (of course!). I bought a new one that matched his receptacle but it has four wires and the old cord had three. The four wires are black, red, white and green. I figure the red and black are the hot wires, the green is ground and the white is neutral. How should I connect these to the three screws on the dryer? The old wires were red and black to the hot posts and the green to the ground post (which is also wired to the frame and chassis). Can I connect the white to the ground post? Should I connect the white to the chassis or frame? Or do I have to pay someone to change his receptacle? Thanks for any advice!


Dear MN,

You are correct in you determination of the purpose of the four wires. Some electrical codes require a separate wire (green) for the grounding of the BODY of the dryer. In a three wire cord, the neutral and body ground share a common terminal.

Look at the ground wire connection on the dryer. There should be a metal bracket, called a grounding strap, that bridges between the neutral terminal and the body of the dryer. Remove it and connect the white wire of the cord to the grounding terminal, and the green to the body-side screw for the grounding strap. If, for some reason, there is not a screw to attach this wire to, you could drill into any part of the metal frame and attach the green wire using a sheetmetal screw. Scrape off any paint around this connection to be sure of a positive ground.

Of course, if you are unsure or don't feel confident about doing this, get an electrician or appliance repair guy to finish the installation.

Dear NH,

I just purchased a new home and we had to buy a washer and dryer. When putting in the dryer where the old one was originally installed (in the basement), I noticed there is no vent to the outside. Is it dangerous to just let it vent out the back of the machine or should I cut a hole to vent it outside ?

JG from East Bridgewater, MA


There are a few potential problems in letting your dryer vent into a room, be it a basement or anywhere else. The two problems are excessive moisture and lint. Clothes dryers can add enormous amounts of moisture to the air. This may be somewhat desirable if the inside air is very dry, as in the winter months in colder climes. However, in a basement this is rarely the case. Even in well-constructed basements there is a constant struggle with moisture. Adding more is not beneficial and can increase mildew growth and the likelihood of other moisture related problems such as paint lifting in outside walls. Basement moisture can have wide ranging effects!

The second problem, lint, is as insidious. These particles of wool, cotton and other clothing materials that are shed in the drying process are never completely caught by the lint filters in clothes dryers, so they escape in the dryer exhaust. Allowing this lint to become airborne in your home not only adds to the amount of unattractive dust on your furniture and floors but could lead to or exacerbate sensitivities of any allergy prone people in your home. Add to this the scents and chemicals released into the air through the detergents left in the clothes and the use of fabric softeners in the dryer, and you can see why I don't suggest leaving a clothes dryer unvented!

There are special lint catching devices that can trap most of the lint. They work by routing the warm moist air from the dryer over a container of water. As long as you remember to keep adding water they work fairly well. You can purchase one of these at many hardware and home stores.

IF you were in the market for a new dryer and washer (and for the benefit of our other readers), there are combination clothes washers/dryers that are designed to be unvented. They have sophisticated lint catching systems plus higher intensity spin cycles so that the laundry is as dry as mechanically possible before the actual air drying begins.

In your case, though, installation of a vent is probably the way to go. The hardest part of the job is boring the 4 1/8" diameter hole through to the outside. Since most folks won't want to purchase an expensive hole saw for a one-time project, I suggest renting one if possible from your local rental store.

If you have a convenient window, you might be able to get around a "boring" job by fabricating a vent. Replace a pane of glass with a galvanized metal sheet with a 4 1/8" hole precut into it. Because of the extra stress of the dryer hose, glue the sheet metal in place with caulk instead of using window glazing putty. Then attach a standard dryer vent cover to the sheetmetal and your ready to go!

Dear NH,

Here is a handy tip I heard on the radio recently. To make cleaning your dryer vent easier disconnect the vent from the dryer and use a leaf blower to blow out the dirt and lint! Works like a charm! Thanks for the great newsletter and website!



Thanks for writing and for the great tip. This method, tried and true, will indeed remove many blockages that occur within dryer ducts.

Over many years lint tends to build up in dryer ducting even with regular blowouts. The dampness of the lint is the culprit as well as any protrusions into the pipe that may give the lint a place to "catch" and start to accumulate. The folds in flexible ducting can also contribute to this buildup by slowing down the air movement in the hose. Once this "plaque" begins to seriously block the hose, blowing and other mechanical methods may or may not work. In the case of flexible ducting, replacement is the repair of choice.

In-the-wall ducting… not uncommon in many older homes… is both difficult to clean and even more difficult to replace since the walls have to be cut open to do it! There is no duct cleaning equipment that will work in flexible ducting since the equipment can damage the ducts. However, if all your ducting is modern solid metal pipe, heavy-duty cleaning is possible but unfortunately the equipment is not readily available to the amateur. This forces you to hire a duct cleaning service.

By the way, I hope the radio announcer said to only use an "electric" blower, not a gas powered one! Could make things in your laundry room a little stinky and a lot dangerous!

Dear NH,

I'm moving into a newer house and the electric clothes dryer has a 4-wire connection. (my old dryer had 3-wires). I bought a new 4-wire power plug. I connected it just like the other was connected but the 4-wire cord has its own ground wire. What do I do with the old ground wire that is connected from inside the dryer? Disconnect it? Leave it??



First things first... if you don't feel confident in determining the hot, neutral and ground connections, call in an electrician to do this hookup for you! If you reverse the wiring it could be disastrous! Luckily, most replacement plugs come with a schematic describing what wires and prongs are for which connection. Though I don't get too deeply into electrical issues, I know this is one job that many DIYers attempt so I will try to give a simple explanation of the process.

In older 220 volt clothes dryers that utilized a three-wire plug, two of the prongs were "hot"... each carrying 110 volts, and the third was the "neutral", which also doubled as a grounding wire for the metallic body of the dryer. The neutral wire completes the electrical circuit back to the main electrical panel and then to the ground.

The latest electrical code requires a fourth prong on all 220 volt plugs. This additional plug is a separate ground for the appliance frame. The separate ground is a backup in the event the neutral wire becomes disconnected... for safety reasons, of course. Should one of the hot wires accidentally touch the body of the clothes dryer, the rush of electricity to the "ground" will cause the circuit breaker to trip and turn off the power. By having this additional wire leading to ground, there is less chance of the metal frame of the dryer becoming electrically charged... a possibly deadly situation!

Look at the power "block" where the prongs on the plug are attached. There is usually some sort of removable metal linkage that connects the neutral terminal to the body of the dryer. This "bridge" must be disconnected. Then, attach the new ground wire to the body of the dryer. Sometimes there is a screw at the end of the grounding linkage that allows this connection to be made. Or, you may have to drill a hole into the frame and attach the ground wire using a sheet metal screw and a washer.

Test the ground with a multimeter set to check resistance... touch one terminal to the body of the dryer (bare metal) and another to the ground prong on the plug... if you show positive resistance you have correctly grounded the appliance. If your meter doesn't show resistance, check to be sure your ground connection is onto bare metal. You may have to even scrape off a little paint to make a good connection.

Electrical work can be dangerous! If you have ANY DOUBTS AT ALL about your connections, call in a pro and get it done right!