From:

Int'l Association of Certified Home Inspectors ...

The maximum length of a clothes dryer exhaust duct shall not exceed 25 feet (7,620 mm) from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.8 rad) bend, and 5 feet (1,524 mm) for each 90-degree (1.6 rad) bend.

Booster fans can be used with long length runs.More info

I had no idea about 25ft rule - however in that article you linked it also had a "Dryer Venting Comparison Chart" with the manufacturer recommended length and most of them were well over 25ft - what's the difference? Thanks!

""Dryer Venting Comparison Chart" with the manufacturer recommended length and most of them were well over 25ft - what's the difference?"

The International Residential Code is using the lowest common length because nobody really knows which dryer will be installed, and the duct is usually buried in the walls and floors, never to be seen again. The comparison chart is just a cross section of some of the dryers, and also includes flexible duct which is only allowed by the IRC in a short section to connect the dryer. The comparison chart also points out a difference between a type A and type B vent hood. The IRC does not make the distinction, so it has gone by the lower number of the two in the ridgid metal category.

In 2012, the IRC changed its stance a bit and now allows 35' as the maximum length since it appears more compatible with the manufacture specs, and the outside hood could be changed if need be.

http://premiumaccess.iccsafe.org/document/code/362/6129189

The IRC also changed some fine points such as labeling the duct length in 2015.

http://premiumaccess.iccsafe.org/document/code/272/4665944

and don't mind to vent to the front porch (unless there is possibly some code issue there?)

If the IRC is the applicable code, the allowed termination location would be determined by the dryer manufacturer's installation instructions. If there are none, it must be at least 3ft in any direction from an opening into the building.

If you are in a cold climate there will be a condensation plume which might alarm the neighbors the first time they see it so a low location screened from view might be best and not on an entrance porch. There's not enough information for us to help you with that.

You don't want a long dryer vent.

Here's something that happened to us a month ago: We smelled something bad -- obviously something dead -- in our pantry /laundry, and we were able to simply (well, didn't seem so simple at the time) pull the machines away from the wall and remove the vent hose. Once we took the vent hose out to the garbage can, the horrible smell was gone. A little critter had climbed up the ivy on the side of our house and into the vent opening ... but then slid down into the hose and was unable to climb back up.

This was a bad evening for us, and we were very, very glad that our dryer vents directly outside. Imagine how much worse this would've been if the hose had stretched across another room. I have no idea how we would've removed /replaced the hose vent ourselves. Realistically, we would've had to put up with the smell 'til a repair man could arrive -- and, of course, the smell popped up around dinner on a weekend.

They have a electric dryer that ventless that might be a option,I think bosch,Miele,and whirlpool offer them.

The longer the vent the longer it takes to dry the clothes.

Ours is at the front of the house. No issues with that as its not visible as there is a flower bed right there. Might be a bigger deal if it vents on a porch. There tends to be some lint in the area at times and the vent can get quite hot

It would not be wise to trap the moisture under a porch roof, even if it were far enough from an opening to satisfy code.

Venting a dryer through a roof is another "fat house" solution that is a poor choice. Mainly because almost no one does the recommended duct cleaning. Lint is heavier than moist air, and can form an impenetrable mass filling the duct, and creating a very dangerous fire risk.

The best solution is to properly site the laundry room on an exterior wall where it can be vented directly out.

If the IRC is the applicable code, the allowed termination location would be determined by M1501.1 "Outdoor discharge. The air removed by EVERY mechanical exhaust system shall be discharged to the outdoors in accordance with Section M1506.3. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space."

Which M1506.3 also says that openings shall comply with Sections R303.5.2 "Exhaust air shall not be directed onto walkways" and R303.6 "Outside opening protection".

Section M1502.3 ALSO applies.

Neither the dryer manufacturer's installation instructions, nor M1502.3 cancel out the general provisions of M1501.

Thanks everyone for all the info - so what's the lesser of two evils - run a 30-40 ft line to the back of the house or a 5-10ft line to the front of the house that dumps onto a covered porch?

The shorter and straighter, the better. Things dry faster.

I'd prefer venting onto a veranda area over running it through several rooms.

If the metal duct will be exposed in the basement, has a booster fan located near the end of the run and has few turns it should be fine. A good fan will have an indicator at the dryer showing if it is operating properly and will shut down if the temperature rises too high.

Are you sure the duct can't run above the foyer or garage?

If the front wall under the porch roof has good exposure from the sides and the termination is near one side and not near openings, seating areas or obstacles like plants are more than 12" away, that can probably work too. Perhaps the duct can be extended vertically so the termination is above the porch roof.

Perhaps the laundry can be moved.

IMO you are likely to have prevented us from suggesting the best solution by not posting the plans and elevations of the house.

LINK to Fantech

Obviously don't vent it out of the front for aesthetics, but that run is waaaay too long for the back. Vent it out the side wall.... This allows for it to be functional but still look fine. Look at the heartland type wall vent for positive seal on the dryer vent which is also easily cleanable for the lint.

Have you checked into the condensing dryers, no vent required?
We are entertaining it.

Condensing dryers are great as long as you don't mind waiting 2-3 hours for your clothes to dry and I'm talking about small loads. We don't even bother doing things like sheets and towels in it anymore because that could take all day to dry. We have an Asko condensing dryer in our apartment and I will never get another condensing dryer again. I have to run the dryer 2 and 3x for anything to dry thoroughly.

Add to that if you are planning on having the dryer in a closet and not in a room, it will mean keeping the doors to the closet open the whole time the dryer is going. Otherwise the dryer won't get enough air to work properly.

Or get a louvre closet door, or have an intake grille on the door equal or greater than 50 sq inches.

100 inches²

Condensing clothes dryers remove water from the dryer air by condensing it into a liquid so there is no ducted exhaust and no makeup air needed. These dryers are exempt from IRC M1502 and IBC 504.

If ventilation air is required by the manufacturer, it is because some units use small blowers to circulate air across a heat-exchanger inside the dryer or draw in room air to cool the interior air and condense the water.

Edit for less confusion (epic fail on my part):

.

Although there is no requirement to provide an exhaust, fresh air ventilation must be available to a condensing dryer so usually a closet door cannot be solid or it must be open when the unit is operating. These units don't really work in small spaces unless there is mechanical ventilation provided. However, it might be easier to supply outside air to the OP's laundry room than to provide a dryer exhaust.

Vith - "Where a closet is designed for the installation of a clothes dryer, an opening having an area of not less than 100 square inches (0.0645 m2) shall be provided in the closet enclosure." Is a separate sentence from the one with "200cfm" in it, and they are not dependent on each other. One sentence has little to do with the other, except that they both have to do with dryers.

The air that is forced through a 4" duct has a velocity. The passive hole in the wall needs to have a larger cubic inch measurement than the forced air hole per all mechanical codes to move the same amount of air. Otherwise, the forced air vent will try to draw makeup air from unintentional places like gaps in the building envelope or cracks under the walls. This in turn promotes mold growth at the unintended cracks, and provides a negative pressure that can draw radon out of the ground, just to name a few problems.

A=πR² = 12.566

The CFM is determined by the velocity, not just area, which is determined by the size of the fan and how much negative pressure is in the room, and back pressure in the duct. That is why every dryer listed in the comparison chart has different allowable duct lengths.

JDS, I dont think Vith was responding to anything to do with the condensing dryer, just the general part of "if you are planning on having the dryer in a closet and not in a room, it will mean keeping the doors to the closet open the whole time the dryer is going. Otherwise the dryer won't get enough air to work properly." that applies to all dryers.

You are right the two sentences are separate, so throw on a 10x10 grille and call it good to make code happy. A bit overkill for a 4" duct but... if its a gas dryer then it needs combustion air also, so yea they have their bases covered. Everyone's happy.

I don't know what left field you were in with this,

Vith said:

If you say so, but ask any HVAC tech, maximum CFM is for the most part is 2 CFM per sq in. LOL at myself, I was thinking 6" duct. 4" is mu...

But, this chart shows 100cfm÷ 12.566 in² (4" duct) = 7.958 CFM per sq in.

200 cfm ÷ 2 cfm per sq in. = 100 square inches for a passive (no fan) air opening. (200 being the number before additional makeup air is required, first sentence) & (2 being the number you pulled out of your ... ;)

The free area through louvers grills and screens shall be used in calculating the size of the opening required to provide the free area specified.

An 8" duct has a 50 square inch cross section. ;D

Cpartist was obviously talking about a condensing dryer needing ventilation air not makeup air.

I think this subject has been taken as far as it can since the OP isn't willing to post plans and elevations.

Yes I was talking about a condensing dryer.

I allowed myself to get talked into (by the subcontracting plumber) putting the washer/dryer in the second bath, because it was going to be large enough, turning the original laundry area into a pantry -- the idea was great on all counts except that one -- I will be venting 7-8 feet (horizontal) to the outside -- of course, add in height, it's more like 15-18 feet.

I plan on doing yearly vent cleanouts, and I already planned to do most of my summertime drying outdoors on clotheslines -- hanging a pulley system off the bedroom end of the deck over to a tree or to a pole. (Don't worry, neighbors won't be able to see it!) The only 90 degree bend in the vent should be where the vent exits the dryer and goes into the wall behind it. But this reminds me -- should I have the vent enter the wall directly behind, or angle up to a place close to the ceiling, and then enter between the wall studs there? (That bend would still be very easy to access, more so than the one behind the (heavy) unit...)

(PS, there are so many things to keep track of, but this one is dang serious -- fortunately I'm now retired as of last week, and so no more mind-numbing 11 hour workdays with some weekends tossed in... I have seen the exit vent from the back of the house, and it goes out over the deck, but no hole has been carved into the sheetrock in the bathroom/laundry yet. I'll get full details when I go back up this weekend.)

Read the manufacturer's installation instructions for the dryer and add the equivalent length for the duct bends. Above a certain equivalent length you might need a booster fan like the ones made by Fantech. A booster fan would go as close to the exterior termination as possible and might even be on the outside of the house.

Thanks very much JDS. I'll keep this in mind when I am picking out the dryer.

@ artemis_ma

"But this reminds me -- should I have the vent enter the wall directly behind, or angle up to a place close to the ceiling, and then enter between the wall studs there?"

These keep the bends and kinks to a minimum, which keeps the lint moving to the outside. Perhaps your builder could build something like this that goes from the floor to a little ways above the dryer. Put a door on the part above the dryer for looks.

@Lily'smom, dryer vents carry out moisture. It would not be very cordial to great your guests with an icy porch in the winter.

We don't know if the house is in Florida or Alaska. We don't know how many stories it has. We don't know why the shorter distances to the sides of the house are not possible or why the duct can't rise above the front porch roof. In short, we only know there is a vented dryer, a front porch, a basement and that 2 unacceptable dryer exhaust duct locations have been proposed. That leaves a condensing dryer as the only reasonable alternative but Nic seems to have lost interest and the thread drags on.

...and the thread drags on... so, just don't let the door hit you in the @s on the way out.

I haven't lost interest :) - was just waiting until I got some more info from the builder. If I am ok with it they will vent to the front porch, but we haven't discussed the exact spot yet. Attached is the floor plan - it's not real clear, but the covered porch runs the full length of the front. To the right of the mud/laundry is the attached garage. The dryer will be installed on the shared wall with the entry way closet. Thanks

And the house is in Ohio

That's not a bad idea - the house is on a couple of acres - so no restrictions or neighbors to worry about

If you're on a couple of acres why not push the garage back so then the dryer can vent out the side

This has me concerned as it looks like we will have a fairly long run either up and out the roof, or out through the garage by the service door. I think up is the better option. Above the garage is an unfinished bonus room.

We have a wraparound porch so our dryer vent goes down and out the base of the porch (i.e. not under the covered area). Ours vents off the side porch though, would having it in the front bother you?

Probably wouldn't bother me, but the covered patio is going to be a concrete base

I still do not see the reason the vent cannot go out the side of the house, according to your floor plan it should be easily do-able. Heck, if its concrete wall they have to go through they can get a core bit and drill a hole.

It's not clear on the floor plan, but the wall that runs to the right of the laundry room is the garage. That garage wall also extends the width of the front porch. There is a great room behind the garage (connected to the dining room) so we can't shift the garage)

There is a great deal of experience and expertise on this forum. Rather than eliminating possibilities and providing incomplete drawings, give us all of the information and let us determine what is possible. That's the way problems are solved on design teams.

A straight run through the garage might allow the duct to be cleaned from the exterior with a standard chimney brush and sectional rods. The dryer might move to the wall shared with the garage, in fact, IMO that corner of the house could use a redesign.

Presumably there is a second floor. If the second floor extends to the front wall, the duct might rise up and discharge above the porch roof.

It is not clear on the edited plan what is to the right of the porch but if it is the wall of the garage that might be the shortest route.

I will see if I can get a full drawing

I'll share my experience with a long dryer run. Our dryer is in a laundry closet underneath the stairs smack dab in the very middle of the house. When we moved in, the run was approximately 30 feet to the front of the house and had six (yes, 6!!!) 90 degree turns. It went up, around, over, under . . . you get the idea. We had constant problems with clogging and even ruined a dryer ($$$$). My husband shortened it by 12 feet and got rid of two of the turns and vented it to the porch instead of the front of the garage. I walk by the vent everyday and don't even notice it, even when it's running. It's still a fire hazard though, and we take it apart at the elbows and clean it often. It's a big production to do this because of the lack of access to it, but you would be amazed at the amount of lint that collects in a very short period of time.

Next house, the dryer is up against an outside wall and will vent directly out. I'm thinking less than a foot of run.

Suru, your original duct "equivalent straight length" was more than 60 ft. It's a wonder that your clothes ever got dry or that the installation was approved by a building official. If the duct was accessible enough to clean, you might have been able to add a booster fan near the discharge with an indicator light at the dryer and a fan that would turn off when the exhaust air was too hot. You probably still need one.

The duct run doesn't need to be less than a foot with no turns. Mine is 30 years old with probably an equivalent length of 25 ft. I check it every 10 years and have never found any lint in it.

The most important source of information about the installation of a dryer exhaust came with the dryer.

JDS, THANK YOU for the info about a booster fan. I didn't know something like that existed so I'm definitely going to look into that. This is a track home that we moved into when it was 11 years old and that was how the vent was installed. I really don't know how it passed inspection and I assume all the other houses in the neighborhood like mine have the same set up. Anyway we will be living in this house for at least 8 more months so I think it will be worth it to get that fan. We cut out the drywall in our garage so we have access to the duct, so we should be able to install it. Then maybe I can finally patch the drywall :-)

This dumb dryer vent is always a concern to me. When we found out how crazy the run was I was told to never leave the house when the dryer is going because it could easily catch fire. It works much better since my husband shortened it, however, the last time we cleaned the run, we still pulled out a 3 foot long chunk of solid lint that had backed-up at one of the elbows. We check it at least twice a year and that is usually the case. Lesson learned: Go with a shorter run if at all possible.

If ductwork is exposed in the garage it must be of a certain gauge of steel. A booster fan should be as close as possible to the exterior discharge. Fantech makes a booster fan that mounts on the exterior of the house. These fans have vanes that allow lint to pass.

Personally I would never leave the house with a dryer running even if the run was directly to the outdoors. Thankfully my Mom was home many years ago when her dryer vented directly to outside caught on fire.