Clothes dryer vent totally blocked with water (C) Daniel Friedman Clothes Dryer Exhaust Venting FAQs

  • CLOTHES DRYER VENTING FAQs - CONTENTS: Dryer vent questions & answers, troubleshooting, safety, repairs, frequently-asked questions (FAQs) about Clothes Dryer Vents, terminations, draft inducers, lint filters, Duct, Screen, & vent Installation Specifications
  • POST a QUESTION or READ FAQs about clothes dryer exhaust venting, ducting installation procedures, codes, standards
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Clothes dryer exhaust vent & screening questions & answers:

Frequently-asked questions, FAQs, about clothes dryer venting: vent distances, terminations, location, routing, draft boosters, lint filters, fire safety, vent booster fans, vent length, diameter, materials, cleaning, and other dryer vent questions, answers, problems, solutions.

This article series describes good practices for clothes dryer vent installation, lint traps, wall vents, filters, and screens. We include a list of clothes dryer fire safety hazards and other clothes dryer installation or maintenance mistakes that are either unsafe or that interfere with effective, economical dryer operation. We discuss types of dryer vent ducting and dryer vent doors or opening protection devices

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Clothes Dryer Exhaust Vent FAQs

Dryer vent installation, sloppy (C) D FriedmanQuestion: dryer vent that is easy to clean but keeps animals out

Aug 15, 2014) Karen said:
This is a very helpful article. Can you please recommend an exterior animal proof cover that can be easily cleaned?

[Click to enlarge any image]

These questions & replies were posted originally at CLOTHES DRYER VENTING - home page for this topic.


Karen, the self-closing horizontal louvered dryer vent covers have done a pretty good job of keeping animals out of the vents I've inspected.

Above in this article we show another type - see this image -

that might work for you.

Those seem to work well against birds and rodents.

If you've got a different animal problem let me know.

DO NOT put a screen over the dryer vent. The screens clog with lint creating a fire hazard.

Question: distance from dryer vent to A/C or heat pump condenser unit

(May 10, 2015) Ryan said:
Is there any minimum distance standard that a dryer vent should terminate away from a A/C condenser? My neighbors dryer vent terminates about a foot away from his condenser. It seems to me that this could allow lint to blow all over the fins of the condenser reducing efficiency and possibly shorten the life of the condenser. Any idea? Thanks.



Clearance distances for air conditioners are given at

I haven't found a code citation specifically addressing clothes dryer clearance to AC unit condensers but that topic is discussed in the article I cite above.

I agree that regardless of distance, if lint is clogging the condenser fins that's going to be a problem. There also *might* be a problem from hot air exiting close to the condenser too.

Question: why does the dryer vent get so hot

(July 25, 2015) Hope said:
We replaced all of our dryer duct work today. Used 4 inch solid duct to outside wall. When we turn the dryer on the duct work becomes so hot. Almost to the point that you can not touch it. Can you please suggest what may be causing this. The dry is about 7 years old and has a new heating element as of 2014.
Thank you!

Reply: clothes dryer house fire statistics


Watch out: you could be facing a fire hazard from an overheated clothes dryer that can set lint or clothing on fire. Flynn (2008) found that in nursing homes she studied, clothes dryers or washers were involved in 12% of the fires - more than double the number of fires ascribed to heating equipment. A more broadly based Canadian study (Wijayasinghe 2011) found that overall 4% of house fires were traced to clothes dryers.

Typically I see hot dryer exhaust when the dryer air circulating-intake lint screen is clogged; or if you've pulled the lint filter on your dryer and cleaned it you may need to look for and vacuum out additional lint that leaked around the lint screen and that is blocking the dryer's air flow.

A second cause of hot dryer exhaust might be a blocked dryer outlet vent or clogging anywhere in the length of the dryer vent ducting.

Question: reader promotes a pest resistant dryer vent

6 August 2015 Kelly said:
I am confused, in the above captions one place it says Watch out: do not eave off the dryer wall vent rodent screen: And lower down with the same picture it says.

DO NOT PUT A SCREEN that will block or collect lint on the exterior of a clothes dryer vent as you may cause dryer overheating and a fire.

Example: the 2009 International Mechanical code 504.4 says -

Dryer exhaust ducts for cloths dryers shall terminate on the outside of the building and shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination.

The only product I found to comply with this and keep pest out is the No Pest Vent. We put them on our dryer and bathroom vent fans, no more birds, mice, bees, etc and our laundry and bathrooms are warmer in the winter because it has two doors the close that keeps the backdrafts out. Actually our drying time is less as well because it flows air better. I would recommend this product for anyone having pest problems or simply for the efficiency and energy savings.

Reply: don't confuse dryer vent louvers or flapper opening doors that keep rodents or birds out of a dryer vent system with an external screen that traps lint and forms a fire hazard


We want what Timm (1983) pointed out (as have others) a dryer vent that lets moist warm air vent out, doesn't invite pests in, and doesn't clog with lint. That is we want to assure:

- rodents or birds to be unable to enter the dryer vent; most dryer vents have an air-flow-operated flapper or louvered opening that swings open when the dryer is operating, thus allowing dryer exhaust to blow out of the building; when the dryer stops the vent closes and uninvited pests are kept out.

- Some clothes dryer vents include an additional screen over the vent opening that is intended to improve the resistance of the vent to entry by rodents or birds.
Those screens can become lint clogged and block the vent, causing a fire.

Since pests are not likely to try to enter a dryer vent when the dryer is actually operating, you want to be sure that when the dryer stops the vent closes fully - whether it's a single flapper door OR a multiple-louvered vent covering. I have found that BOTH types of doors can become clogged with lint and may then fail to close fully. A third type of dryer vent uses a sliding plastic "can" structure that lifts up to vent when the dryer runs and closes positively when off. That

The No Pest Vent people, whom I suspect you represent, sent me an email today advertising their product.

At the end of the day, you want a dryer vent that keeps pests out but doesn't trap lint and cause a fire. While the product you cite may be a fine one, there are dozens of dryer vents on the market that open to let moist dryer vent air out when the dryer is running and close adequately to keep animals out when the dryer is off.

That's what is called for by typical clothes dryer installation instructions. The product you name is not a requirement. Your comments are perhaps a bit of an advertisement.

Watch out: in our experience all of the clothes dryer vent openings, flappers, louvers or air-operated opening and closing dryer vents that we have installed or inspected need periodic inspection and occasional cleaning for safe, effective operation.

Question: move our dryer to the garage from the inside of the home

(Oct 26, 2015) JR said:
I'd like to move our dryer to the garage from the inside of the home.

Ventilating would be better suited as it would be a horizontal exhaust as compared to the current vertical one we have now.

My question is can the exhaust pipes be exposed to the garage or does it have to be behind drywall? I live in California so does it require certain building codes for dryer vents? Thank you

Reply: California clothes dryer vent code citations

I'd ask your local building department about local codes. Dryer vents should terminate outside of the building (not in the garage).

In general clothes dryer vents do not have to be enclosed in building walls. Be sure to check the dryer vent lengths and also the number of bends or elbows in the vent system against what your dryer manufacturer agrees is safe. In California (USA) the ventilation requirements for clothes dryers are specified by the following:

California” Uniform Mechanical Code. Sections 504.1 and 504.3. Section 504.3.1

Section 504.3.1 Dryer venting shall terminate on the exterior of the building and will have a back draft damper (flapper). Screens shall not be permitted or installed at the dryer vent termination. Clothes dryer vent pipes shall not pass through or extend into other ducting or plenums. Dryer ducting shall not be fastened with screw type fasteners which may impede the air flow or catch lint, yet must be fastened and sealed “substantially airtight” at each joint. (An approved fastening system is aluminum duct tape)

Section 504.3.2 A minimum of a 4-inch diameter duct is required.

Section 504.3.2.1 Clothes dryer vent ducts shall be metal and shall have a smooth interior surface. An approved “flexible duct connector” of not more than 6 feet in length may be used to connect the dryer to the dryer vent pipe. “Flexible duct connectors shall not be concealed within the construction.” (Flex duct connectors shall not pass into or through a concealed space. This includes cabinets, walls and attic spaces).

Section 504.3.2.2 A dryer vent duct shall not exceed the maximum length (horizontal and/or vertical) of 14 feet including two (90-degree) turns without a mechanical upgrade. Two feet of length shall be deducted for each additional 90-degree turn. 

Question: installing a dryer vent in the second floor

(Nov 23, 2015) Kevin said:
I am installing a dryer vent in the second floor with a very short horizontal run. My concern is if there is an issue with the distance from the vent exhaust to the second floor roof. I live in the mid-west an we get cold weather and snow. I am concerned about causing an ice dam at the fascia and gutter area. It would be approximately 12-18" above the shingles


I don't quite have the picture - you can use our page bottom CONTACT link to send me a sketch.

If you mean you're venting vertically up through the roof, the heat from the exhaust will certainly melt snow that is blown down-upon from the vent, and worse, if there is a deep snow cover and freeze/thaw the vent could freeze shut and cause a dryer fire.

If you're venting out through a side wall, gable end or soffit, insulation of the dryer vent ducting may do the job.

Question: safe to vent almost directly to the outside?

(Dec 3, 2015) Anonymous said:
is it safe to vent almost directly to the outside (opening to outside located just above floor and dryer vent at same level



I'm not sure I understand the question correctly. But if you are asking if very short dryer vent distances from dryer to the building exterior are safe - sure as long as the other requirements specified by the manufacturer for venting are met such as venting material, connections, routing. Shorter vents mean less risk of clogging.


Clothes Dryer Vent Termination Clearance Distances

Clothes dryer vent termination without cover (C)

An reader provided this pair of photographs of a clothes dryer exhaust vent termination on the building's exterior wall. Above we see that there is no proper cover on this dryer vent: birds, rodents, or someone else can enter the dryer vent, nest therein, block up the dryer vent, and cause a dryer fire or a buidling fire.

Below we see more trouble with this ugly dryer vent installation:

Clothes dryer vent blows lint on gas meter (C)

The clothes dryer vent, located about 20" above the outdoor gas meter is blowing lint all over the gas meter and its various parts. This might seem harmless but it's not. Lint blockage of the vent port on a gas regulator valve can cause a dangerous gas leak inside the building risking a fire or explosion.

Dryer vent too close to gas meter (C)

I haven't found an explicit model building code giving a minimum clearance distance from a dryer exhaust vent opening to a gas meter (or to the meter's regulator). The minimum distance of three feet clearance from the gas meter to the clothes dryer intake or exhaust vent opening is given by the article cited below. You'll see the three-foot rule commonly cited by gas company specifications such as our second citation just below.

  2. Puget Sound Energy, Inc., "Gas Meter Clearances and Service Installation Requirements(March 2016)", [PDF] new retrieval, 3/26/2016, original source:

Question: how far a wall mounted dryer should be from the ceiling

(Dec 28, 2015) Anonymous said:
Is there a law/guideline how far a wall mounted dryer should be from the ceiling



Check the installation instructions for your clothes dryer - the manufacturer will give the necessary clearance distances.

Common sense will also tell us that the dryer opening and controls have to be readily accessible by a user standing on the floor.

Question: is 24" clearance from dryer vent to ground safe for a 30 foot dryer vent run?

Noah said:
My electric dryer vent, after around 30' of mostly rigid straight pipe, terminates to the outside through a downward facing vent that has at least 2' of space below (before the ground) and likely a reasonable amount of air flow otherwise from left to right. Should I be concerned here? Any reason I absolutely need outside access? Anything I should do?


Noah your installation height sound reasonably good to me, though in areas of deep snow or if exposed to freezing there could be a safety worry if the vent can become blocked by snow or ice or frozen condensate.

That 30 feet is a long run, perhaps longer than the dryer manufacturer recommends. I'd check for soot clogging in the system from time to time. If you notice clothes taking longer to dry or the dryer running extra hot those are signs of dangerous dryer vent blocking.

Question: dryer vent clearance to other mechanical systems: air conditioners, motors, heating equipment, air intakes

2016/03/24 Stephanie said:

What is the required distance between a through the outside wall direct furnace vent and a dryer vent.
I'm renting and they are very close together. I tried to find the requirements myself but was unsuccessful.
Thank you so much

This question appeared originally at INDOOR AIR QUALITY IMPROVEMENT GUIDE


Stephanie: if the direct vent furnace air intake can pull in lint from the clothes dryer the installation is unsafe. Lint clogging the direct-vented furnace could result in vent overheating and possibly a building fire. But that's a subjective opinion on my part as I have not seen an explicit clearance distance stated in model building codes nor installation instructions.

at DIRECT VENTS / SIDE WALL VENTS we find a more general clearance specifications that in my view serve as a reasonable model-answer to your question. I quote:

This article and thus my suggested specification (10 feet) recognizes that dryer lint can clog a key vent such as on a gas regulator at a distance of 4 feet nd that a significantly greater distance would be needed for safe clearance between a clothes dryer vent outlet and the air inlet of any mechanical system such as a direct vent chimney sidewall or rooftop penetration. That's a reasonable minimum distance of 10 feet.

The local building code official is the final authority on questions like this, particularly as there may be site conditions that for safety should change general safe clearance distance recommendations.

at A/C CLEARANCES from OTHER MECHANICALS where we discuss distances from a dryer vent to an air conditioner compressor, we include the following:

Photograph of air conditioning compressor condenser units with many problems

In our photo above, from a Minneapolis MN home, these two compressor/condenser units are just about three feet apart - a little close, and that right-most larger compressor/condenser unit is too close to building walls, a clothes dryer vent, and shrubbery.

We also see that direct-vented heating appliance white PVC piping is blowing exhaust close to these units. The installation is nice-looking and neat though.


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