# Vertical equivalent of horizontal dryer vent



## Wayfarer Doors (Feb 2, 2010)

Sorry to ask this, it should be a simple answer, but no one says specifically what it is. I'm repairing some stuff at an orphanage in Chiapas Mexico. 2 gas dryers vent directly inside, with some ventilation about 16 feet up. Manufacturer says it can go 28 feet to vent outside, but I'm assuming that is horizontal, not vertical.
So for a 4" dryer vent, "what is the vertical equivalent of horizontal"?
Thanks


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## flashheatingand (May 3, 2008)

I believe you can go straight up to 20'. If you are only using one elbow. Having said that, I would call the manufacturer if in doubt.


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## GettingBy (Aug 19, 2010)

Wayfarer Doors said:


> 2 gas dryers vent directly inside, with some ventilation about 16 feet up. Manufacturer says it can go 28 feet to vent outside, but I'm assuming that is horizontal, not vertical.
> So for a 4" dryer vent, "what is the vertical equivalent of horizontal"?
> Thanks


Since the air is warm the stack effect will assist in venting the air so if you're allowed 28' horiz you're allowed more vertically.


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## txgencon (Jan 4, 2011)

GettingBy said:


> Since the air is warm the stack effect will assist in venting the air so if you're allowed 28' horiz you're allowed more vertically.


That is absolutely not true. Air has weight and the moisture in the air adds even more weight.


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## Rio (Oct 13, 2009)

The last time I looked at the IBC (International Building Code) it was 14' maximum; not sure if that included vertical. A problem with going vertical is the lint will have more of a tendency to fall out, posing a fire hazard eventually. There are assist fans to help with exhausting and maybe consider additional lint filters?


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## Wayfarer Doors (Feb 2, 2010)

ok, so next question, since there is no HVAC to speak of here, ridgid duct is hard to come by, I'd lke to use PVC but heard that there is a static problem causing lint to accumulate.


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## flashheatingand (May 3, 2008)

Just make sure that it is easy to clean out with a brush, and you should be ok. Lint builds up just as much horizontally and often is much harder to clean, especially if there are a lot of elbows.


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## GettingBy (Aug 19, 2010)

txgencon said:


> That is absolutely not true. Air has weight and the moisture in the air adds even more weight.


At what RH and temp. do the grains of moisture in the air cancel out the stack effect due to warmer air being less dense than colder air?


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## txgencon (Jan 4, 2011)

GettingBy said:


> At what RH and temp. do the grains of moisture in the air cancel out the stack effect due to warmer air being less dense than colder air?


I really don't know the exact figures, but I suspect it doesn't take much. I mostly know from personal experience. I once had a house that had the dryer back up to a double 2x4 wall. The vent (4" all the way) went into this wall and then turned and went straight up through the roof for a total run (from the 90 bend at the floor) of about 17 feet. It would take a couple of hours to dry a load of towels. Since the laundry room backed up to the garage, I changed the vent to run through the wall, turn and run horizontally about 19 feet to the outside. After that, a load of towels would dry in about 40 minutes. That wasn't nearly as good as it had been at our previous house (same dryer but it simply vented straight outside - total run about 1 foot) where a similar load of towels would dry in 30 minutes. This was quite a while ago (in the 80's). Modern dryers don't dry as quickly as the older models as they are "gentler" on fabrics.

Even this article http://www.appliance411.com/faq/dryer-vent-length.shtml doesn't provide an exact reduction of length recommendation for vertical venting. It just says "Vent length for vertical installations should likely be *considerably* less than the maximum lengths quoted which are geared to regular horizontal vent installations." 

I think another thing that happens in a vertical venting situation is that the moisture-laden air cools as it travels and the cool air tries to fall back down the vent and creates a sort of thermal block. One of the first things I checked on when I was having the problem with the vertical vent was how much flow there was (that is, after checking for a blocked vent). It was almost undetectable. With the horizontal venting, it would blow the shrubs pretty good.


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## flashheatingand (May 3, 2008)

When comparing the dryer times, was the vertical pipe cleaned of lint? To be fair in the comparison, I would bet the verticle pipe was dirty and the horizontal run was clean, and that would effect the dryer times.

Don't get me wrong, if one can vent directly outside, that is the ideal way to go. But, if you have to go either down, or straight up, I would go up. The reason being is that it is easier to clean.


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## GettingBy (Aug 19, 2010)

txgencon said:


> It would take a couple of hours to dry a load of towels.
> 
> After that, a load of towels would dry in about 40 minutes.


I stand corrected.


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## txgencon (Jan 4, 2011)

flashheatingand said:


> When comparing the dryer times, was the vertical pipe cleaned of lint? To be fair in the comparison, I would bet the verticle pipe was dirty and the horizontal run was clean, and that would effect(sic) the dryer times.
> 
> Don't get me wrong, if one can vent directly outside, that is the ideal way to go. But, if you have to go either down, or straight up, I would go up. The reason being is that it is easier to clean.


I was the first owner of the house (which had been used as a model home for about two years). I don't think they had a dryer in it during that period. I figured it had some sort of obstruction but I put a flashlight at the bottom and (after removing the cap) could see that it was a straight 4" run. It didn't have any screws sticking in so it looked like it had been done correctly (taped with foil tape). The part I could see in the attic even had foil tape on the joints used to make the pipe (the longitudinal joints). I swabbed it out using a small rope and damp rag but didn't get much. I tried it without the cap for a few days but it didn't make an appreciable difference.

I went from that to a completely horizontal vent (one 90 degree bend at the back of the dryer). I did use 4" PVC for most of the run (except for the 90" degree bend and the vent cap assembly. I didn't notice an abnormal buildup of lint from static electricity but can see where that could be a problem long term. It is important to clean the vent occasionally, regardless of the length.

I imagine any venting arrangement that goes down and then back up to exit the structure would be difficult to clean as the debris would tend to get caught in the resluting "trap".


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## flashheatingand (May 3, 2008)

Good to hear about the difference in drying time.


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