Home Inspection Confidential

Almost every Home has one, most of the time we don’t think about it, and it is a contributing factor in a third of all house fires. It’s your clothes dryer vent.
The purpose of a clothes dryer vent is to transport the hot, moist,lint-laden air from the clothes dryer to the outside of the home. That sounds simple enough, but there are MANY things that can interfere with this very simple process, and that can lead to a catastrophic fire.

Step One: Dryer to Vent Pipe

Ideally, the dryer should line up with the connection point on the laundry room wall and just pushing the dryer to the wall would connect everything and there would be no “connection”.  I have only seen this ONCE in 6 years.

Unfortunately, what I see most often is a complete 12-foot-long section of flexible dryer vent hose used to span an 18-inch gap, with all the extra length twisted up and stuffed in a pile behind the dryer, like in this house:

Excess dryer vent hose stuffed behind dryer

Why This Is a Problem

First of all, just using the flexible spiral pipe can void the warranty on most dryers. Next, the 12 foot length of that coiled-up pipe has just used HALF of the total length of dryer pipe allowed. And last, regardless of what the package says as to approvals and the like, flexible dryer pipes are a FIRE HAZARD. Why? Because they are not SMOOTH on the inside, so they collect lint, causing “hardening of the dryer vent,” just as arteries in the body are blocked with cholesterol.

Clogged dryer vent

Once the dryer vent becomes clogged, the dryer takes longer to dry your clothes, has to work harder to dry those clothes, and costs you more money to dry those clothes.  As the dryer is now working harder, it gets warmer, and since the lint can no longer get out of the dryer, it backs up into the dryer, where it builds up and leads to a dryer fire.

The Solution

Best: Use a piece of sheet metal pipe to go the needed distance.
Next Best: Use a METAL dryer connector
Acceptable: Use a piece of SMOOTH BORE Flexible Metal Pipe

We have only connected the Dryer to the Pipe that hopefully goes outside… Now we need to look at THAT pipe…

Step Two: The Vent Pipe

This is the pipe that carries the hot, humid, lint-laden air through the walls of your home and exhausts them to the outdoors.

This pipe should have no interior obstructions, including screws and other fasteners. You want an absolutely smooth interior. The joints need to be facing the OUTSIDE, the pipe needs to be supported, and it needs to be SHORT.

The rule for many years has been that a dryer vent pipe should be no longer than 25 feet as measured from the inlet where it connects to the dryer to the outside exhaust point. Each 45-degree elbow counts as 2.5 feet, an elbow as 5 feet. If the dryer is on an outside wall, we have no problem, but often the dryer is in an alcove in the middle to front of the house. We might have a 90 degree bend at the dryer to go down below the floor, then another elbow to turn it towards the outside, and then because the builder doesn’t want the exhaust vent on the front of the house we go all the way to the back of the house, 35 feet away. So lets calculate what the dryer might be trying to breathe through:

• 12 feet of crinkled/crumpled dryer hose immediately behind the dryer
• One 90 degree turn (counts as 5 feet)
• 2 feet of pipe to get to the basement
• Another 90 degree turn (counts as another 5 feet)
• 35 feet of pipe

So the dryer is trying to push all that wet lint out a pipe equivalent to 59 feet long when the MAXIMUM is supposed to be 25 feet.

This dryer vent hose could be a major safety issue.

Is there a solution for this long dryer vent?  Yes, there are specialty “booster fans” that can go in the dryer pipe to “boost” the flow.  Those fans have their own rules about where they need to be, but they solve SOME of the problems.

Fantech Brochure

Fantech Booster Fan

Other Issues

Dryer pipes in attics need to be insulated. Think about it: you have a metal dryer pipe running through unheated space. This pipe is carrying hot, humid air loaded with lint. In winter, the pipe will be cooled by the cold attic air. The moisture (and the lint) will condense inside the pipe, leading to clogs.

During the 1970s, the energy crisis led people to stop “wasting” the heat from their dryers by venting them inside the house. This isn’t recommended; most gadgets designed for trapping the lint don’t work very well and need to be emptied often. Even venting into a crawl space can invite problems.

I’ve seen dryer pipes that go up through the roof, 2 floors straight up. Hmm; that 25-foot maximum doesn’t say anything about which direction. However, pushing wet lint straight up is certainly harder than pushing out horizontally.

Why Am I So Picky?

Why am I so picky on dryer vent pipes? Because they have the very real possibility of killing people or destroying their homes. Here’s one example about a tragic Massachusetts fire:

Dryer Fire Kills Lexington Mother

I was telling this to one of my clients during an inspection and he held up his hand to signal me to stop. ”Bob, you don’t need to say any more… those ‘people’ you speak of whose home caught fire? I was one of those people… We HAD a fire start in the dryer in our last home.”

This isn’t an urban legend; this is real and very very preventable. THAT’S why I am this picky about dryer vents.

More Information

FEMA statistics on dryer fires

Consumer Reports article on Dryer Venting Safety

Consumer Product Safety Commission advisory on Dryer Safety

This entry was posted on Thursday, March 19th, 2009 at 11:06 AM by Inspector Bob and is filed under Bad Things, Home Safety. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.