Keep water out of my Fresh Air Intake!

[dbooksta]

I have a 4" PVC fresh air intake. I have run it up to 6' above grade and put a U at the end so that the intake is facing the ground. But the suction is enough that when we have heavy rain the intake sucks in a lot of water.

Are there any tricks to preventing the intake from taking in water, short of building a roof over it?

[RoBoTeq]

More then likely it is condensating inside of the pipe, not sucking water in. 4" pipe is a bit large and will condensate quite a bit of moisture from the air.

In any case, you should have a trapped drain on the combustion air pipe close to the furnace.

Concentric terminated vents have the issue much less due to the prewarming of the combustion air.

[trane]

Are you talking about a fresh air for furnace combustion or a pipe that is tied into your cold air return? I have never had this problem on combustion intakes and if its fresh air for return you have a problem with your duct work if its pulling enough to get water to come in the pipe.

[dbooksta]

This is a fresh air intake leading to the cold air return, not furnace/make-up air. It's definitely sucking rain in -- not condensation. I have a FilterVent pulling 75CFM through the pipe, so it's like 1" w.c. of suction. Definitely enough to get rain falling/dripping around the opening.

Once it crosses to the inside of the house the intake connects to a 6" insulated flex duct. Maybe a trapped drain is the solution? Not sure how I would do that on 6" round duct though.

[RoBoTeq]

Sorry, I misunderstood.

[sadlier]

Put a PVC plug on the intake; That will take care of it! :D

If you can find it check out the Rheem condensing furnace direct vent alternative installation diagram. They address that type of problem by installing a T (in your case 4") in such a way that it will trap the water. The side of the T that traps the water has a reducer and then comes off with a hose (about 1/2"). The hose is looped to form a water trap in mid air.

[dan sw fl]

Originally posted by dbooksta
This is a fresh air intake leading to the cold air return, not furnace/make-up air.

It's definitely sucking rain in -- not condensation.

I have a FilterVent pulling 75CFM through the pipe, so it's like 1" w.c. of suction.

Definitely enough to get rain falling/dripping around the opening.

Once it crosses to the inside of the house the intake connects to a 6" insulated flex duct. Maybe a trapped drain is the solution? Not sure how I would do that on 6" round duct though.



Keep It Simple __ Expand That Sucker

SLOW the air down DIRECTLY AT the Inlet ...
IN Other words,
______________ expand 4" PVC to a ~ 6" inlet

Material
1. 4" by 6" Expander (reducer, if you will),
2. 6" diameter PVC x 12"

4" dia., 75 CFM = 860 FPM ... Entrains Water Droplets ! !!
6" dia., 75 CFM = 380 FPM ... Resolved ?

Velocity pressure is reduced by > 4 X

( or as the more dramatic persons wish to
state ' by more than 400% ').

Note: 4" diameter = 12.5 sq. inch,__ .087 sq feet
....__6" __________ 28.3 .........__ .196

[dbooksta]

Excellent solutions -- I'l try enlarging the intake and if that doesn't work I'll put a T-trap on it.

Thanks!