I have an exterior attic vent under the over hang of my roof. The vent is 4"
(I think) in diameter. The vent is one of those air-intake vents with rain
For the last few days it's been below freezing. On those cold days, icicles
appear on the rain guards. The house has an air exchanger (non-heat
recovery) which has been running on those cold days. The house seems to
retain a lot of moisture as the windows tend to either have condensation or
ice at the bottom when it's really cold outside. Also, the house is heated
with electric baseboard heaters.
Before I climb into the attic, I was just wondering if the icicles on the
exterior attic vent is normal? I'm a first time home buyer and I do not
know much about attic ventilation. My concern is that there may be moisture
build up in the attic.
I peaked into the attic. I just stood on the ladder with a flash light as I
didn't know where would be safe to step. What I saw was a lot of blown,
beige or grey insulation (I was wearing a mask). For the most part, the
insulation is evenly spread out. The insulation is severval inches thick
and three is a plastic sheet under it. I can see light from the various
vents, but I couldn't see the actual vents, only the big vent at the peak
of the roof.
The dryer vents through the main floor to the outside on the other side of
the house, so it's nowhere near the vent. The bath fan is connected to a
black pipe that goes straight up and through the roof. I turn the fan on
and didn't see any insulation blowing around.
The wood joists appeared to be clean with no water damage. No signs of mold.
There was some insulation clinging to the joists but I figure it got there
when the insulation was installed?
I can see the tubing for the air exchanger. It's the grey, insulated soft
kind. It was coiled all over the place. Most of the tubing was covered by
the insulation. I couldn't see any obvious sign of leakage.
The air in the attic was cool. The outside temp right now is somewhere
around -3 C (26.6 F). The air didn't smell musty.
What I figure is that the moisture in the house is rising and getting into
the attic - perhaps through the attic door? The vent is right across the
attic door. I'm not sure how else the moisture can be getting in there.
If there is too much moisture in the house, perhaps the air exchanger is
inadequate? It's an Enviro ENV-100 and the house is roughly 1400 sq feet
(each floor is around 700 sq feet). It seems that the blowing in vents
inside the house are working very well. But the suction vents are not very
strong. Perhaps the air exchanger does need replacing - perhaps with a heat
I guess I should contact my local heating store?
ARe you sure that's an attic vent you're looking at? You only talk
about a single 4" round soffit vent, which would be very unusual.
Normally, there would be many of them, or continous soffit venting
along a thin strip. A single one exhibiting this sounds more like a
bathroom fan vent or similar.
Also, what's with the air exchanger? From the description of the
house, it sounds like it's an older one. Unless you have a very
tightly sealed house, where special steps are taken to make it air
tight, which is not common, the house will have enough air leakage so
that no air exchanger is needed. Folks go around trying to seal up
drafts, not use a fan to suck in cold air, which is like leaving a
window open. And if you do have one, I'd be damn sure it was a heat
recovery one, especially with electric heat!
I'm sure it's an attic vent. I'll try explain why. The roof over hangs the
house. On the underside of the roof, there is a white siding material with
tiny wholes. The vent is on this white siding material. On the other side
of the over hang are shingles. From a window across from the vent I can see
duct work. When I was in the attic I didn't see any duct work over where
the vent is located. The over hang part dropped below the floor of the
The house is a semi an is 10-11 years old. The house is pretty air tight.
There are some very tiny drafts that I have found, but haven't looked into
them that much.
I should also mention that on the other of the concrete wall that separates
the two dwellings is the same vent in the same location (relatively). My
guess the houses are identical, just mirrored. When the icicles where
forming on my vent, there were no icicles on my neighbour's vent.
Unfortunately, the darn air exchanger is very old. My guess it was installed
when the hot water tank was installed. I had to replace the hot water tank
already it was 10 years old and started to leak. I definitely know that the
air exchanger is not an HRV model. I've started looking into getting a new
air exchanger. I hope the installation is just as simple as replacing the
old unit. Perhaps the installer would go in the attic and inspect the duct
work to make sure it's ok?
Which makes it even less likely that the vent was put there for attic
ventilation. The siding with the tiny holes on the soffit is
continous soffit venting. Normally, that is all that is used to
provide the soffit venting. It makes no sense to then just add this
one 4" additional vent.
On the other side
Not clear here on what you are seeing here, but if you can see ducting
connected to the vent, again this is not normal for attic venting, for
which there is no reason to connect ducting.
When I was in the attic I didn't see any duct work over where
Probably 95%+ of houses don't have nor need an air exchanger period.
Yeah, since it's below the floor of the attic, I can't really know for sure.
But, I think you are right, it must be a vent for something, I just don't
If that is the case, then the icicles are fine because that means that it is
venting moist air from inside the house and doesn't mean there is moisture
in the attic?
What is typically connected to a 4" vent? I thought the black, vertical pipe
(like the kind the trap for a sink is made of) in the attic was the vent
for the bathroom fan, but I think that may be the vent for the plumbing? I
think drains need a vent to properly drain right??
Thanks for helping me,
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