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Default How to avoid ice-clogged furnace air intake pipe?

Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.
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Default How to avoid ice-clogged furnace air intake pipe?

On Tue, 2 Feb 2010 14:22:41 -0800 (PST), MNRebecca
wrote:

Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.


It sounds like your flue is tilted back towards the house so the
condensate runs back to a low spot and freezes. If this is the
problem, you should put a pretty good pitch on it so all condensate
runs out of the pipe before it can freeze. Another possibility is
that the flue is too long causing a similar problem (freezing before
running out of the pipe). In either case the fix shouldn't be too
complicated. If you can't change the pipe slope or length, perhaps
some insulation is in order.
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Default How to avoid ice-clogged furnace air intake pipe?

MNRebecca wrote:

Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.


I suspect rain and/or snow are blowing (or being sucked) into the
intake at times, along with moist exhaust air. I'd put an extension on
one or both to move the openings further away, then possibly put
another elbow on the intake so it points downward.

Another approach would be to add a "dorade box" (used for on-deck air
vents on sailboats to prevent water from entering) over the intake
pipe. Build a simple wooden box around the pipe end (which points
sideways or upward), attached/sealed to the house, with an opening in
ther bottom of the box. Leave enough room inside the box for free
airflow through it.
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Default How to avoid ice-clogged furnace air intake pipe?

In article , MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless),


He's right. It's less energy-efficient, because cold air is drawn into the
house to make up for it, but it won't harm anything (other than your bank
balance).

it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.


(You sure you don't have that backwards?) That's probably most of the problem
right the the pipes face the wrong directions. The intake should face DOWN
so that rain and snow can't get into it. And the exhaust should face east, not
west: in most of North America, the wind comes from the west much more
frequently than from the east. You want the exhaust to be moving in the same
direction as the wind, not into the wind.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.

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In article , krw wrote:
On Tue, 2 Feb 2010 14:22:41 -0800 (PST), MNRebecca
wrote:

Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe.

[snip]
Any advice on how I can keep the intake pipe from clogging?


It sounds like your flue is tilted back towards the house so the
condensate runs back to a low spot and freezes.


Ummmm.....no, it doesn't sound like that at all, actually. Flue != intake.


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Thanks for all the feedback, everybody. I'll look it over thoroughly.

MNRebecca wrote:
*If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless),


(Doug Miller) wrote:
He's right. It's less energy-efficient, because cold air is drawn into the
house to make up for it, but it won't harm anything (other than your bank
balance).


I'm a little confused by this. The intake pipe draws cold air from
outside. The air in the room is far warmer. Where/how is cold air
being drawn into the house to make up for the fact that I disconnected
the intake pipe and made the furnace use room air instead?

R. (really appreciates what she's learning)
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In article , MNRebecca wrote:
Thanks for all the feedback, everybody. I'll look it over thoroughly.

MNRebecca wrote:
If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless),


(Doug Miller) wrote:
He's right. It's less energy-efficient, because cold air is drawn into the
house to make up for it, but it won't harm anything (other than your bank
balance).


I'm a little confused by this. The intake pipe draws cold air from
outside. The air in the room is far warmer. Where/how is cold air
being drawn into the house to make up for the fact that I disconnected
the intake pipe and made the furnace use room air instead?


When the furnace uses room air instead of outside air, air has to come from
somewhere to replace it. Where do you suppose it comes from?

*All* air that the furnace uses for combustion comes from outside the house,
in the long run. The point of having an outdoor intake for the furnace is so
that the combustion air comes *directly* from outside the house, straight into
the furnace. If the furnace is burning room air instead, that creates a slight
negative pressure in the house, and cold air comes in through various cracks,
leaks, holes, etc.
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Default How to avoid ice-clogged furnace air intake pipe?

On Feb 3, 9:21*am, MNRebecca wrote:
Thanks for all the feedback, everybody. *I'll look it over thoroughly.

MNRebecca wrote:
*If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless),

(Doug Miller) wrote:
He's right. It's less energy-efficient, because cold air is drawn into the
house to make up for it, but it won't harm anything (other than your bank
balance).


I'm a little confused by this. *The intake pipe draws cold air from
outside. *The air in the room is far warmer. *Where/how is cold air
being drawn into the house to make up for the fact that I disconnected
the intake pipe and made the furnace use room air instead?


Doug's answer to this question was good, but I think he fell into the
trap of knowing too much about the issue and giving not enough
information.

Your furnace blows exhaust (air) out the "chimney" (a PVC pipe in your
case)
when it runs. This tends to decrease the air pressure inside your
house, since
there's less air inside.

Normally, your furnace pulls air in through the intake pipe and this
balances the
pressure, but when you disconnect it and use "inside air", air from
outside moves
toward the area of lower pressure (inside your house), through
whatever gaps it
can find (around windows, doors, etc.) This air is colder than the
air
inside your house, which will make your furnace run more to keep the
air in your
house at the temperature set by your thermostat.

Cindy Hamilton
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Default How to avoid ice-clogged furnace air intake pipe?

MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.


A downward facing intake opening would be the first thing I'd try.

You could use concentric PVC pipes, with the intake being the one in the center,
which would keep it warm to prevent freezing. Perhaps a 2" intake pipe, with a
4" exhaust pipe around it. The plumbing at the ends might be interesting. Proper
slope would be important.


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In article ,
MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe

[ ... ]

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.


Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.


Cheap possible fix: Get an elbow that can be attached to your intake
pipe outside the house, pointing it down. That will keep snow, sleet,
hail, etc. from getting in. No need to glue it, just slide it on. If
it's loose and tends to fall off, secure it with a stainless steel
screw through the top, or drill a small hole through and drop in a
galvanized nail.

I really doubt that you have a condensation problem, as winter air is
generally very dry and wouldn't condense going into a warmer environment.
If, however, you're getting condensation from somewhere, you could
disconnect it from the furnace, cut a slot into that end an inch or so
longer than the flange on the furnace, and feed a heat tape through the
pipe to the outside. Use the slot to bring it out at the furnace, and
seal the slot with furnace tape.

The intake should slope down from the furnace end to the outside;
otherwise condensate would flow into your furnace, which would not
be good for it. (This could be a concern in warm weather, unless the
furnace blocks inlet/flue airflow when it's not running.)

If possible, adding a few feet of exhaust stack with an elbow and a
rain cap will help your furnace avoid pulling exhaust back into the
intake.


Gary

--
Gary Heston http://www.thebreastcancersite.com/

"It's kind of hard to rally 'round a math class."
Paul "Bear" Bryant
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Thanks again, all, for the suggestions and the physics lessons!
R.
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In article , MNRebecca wrote:
Thanks again, all, for the suggestions and the physics lessons!
R.



The installers are simple minded. Sometimes snow then water will get
into the switch. First the switch may shut off if there is no air flow,
but if there is some flow the switch can be damaged, and
you have to deal with getting parts. Just like my brothers
up maybe a couple feet, and snow drifts can get higher than that, and have in Md.,
and the forcast is for up to 36 inches in Md this weekend.
There is also a rule of staying away from chinneys and other walls, and optimun
pipe spacing between the 2 pipes is 3 feet.




greg
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Another question. Is it possible the builder/installer (furnace went
in during a major house renovation) made the intake pipe face east
(instead of down) to achieve a 180 degree variance with the exhaust
pipe? They're only a few inches apart. If I add some pipe and change
the intake direction from east to straight down, it'll only be 90
degrees different from the exhaust pipe opening. Have I just greatly
increased my likelihood of carbon monoxide poisoning (from the intake
pipe sucking in exhaust) or doesn't it matter much since it's only
going to get burned up in the furnace anyway?

By the way, I double-checked.
1) They really do face east (intake) and west (exhaust). I generally
think of the wind as coming primarily from the NW in my area, but I
guess it does come from E or SE about half the time.
2) The pipes are about 1 foot above the ground, not 2.5. Maybe the
intake doesn't face down for fear of a drift forming beneath it.
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In article , MNRebecca wrote:
Another question. Is it possible the builder/installer (furnace went
in during a major house renovation) made the intake pipe face east
(instead of down) to achieve a 180 degree variance with the exhaust
pipe? They're only a few inches apart.


Very likely that's the reason.

If I add some pipe and change
the intake direction from east to straight down, it'll only be 90
degrees different from the exhaust pipe opening. Have I just greatly
increased my likelihood of carbon monoxide poisoning (from the intake
pipe sucking in exhaust)


Slightly increased, perhaps, but:
(a) if you don't already have a CO detector in the house, you should anyway;
(b) it's not rocket science to add elbows and extensions to the pipes to
increase the separation; and...

or doesn't it matter much since it's only
going to get burned up in the furnace anyway?


(c) most of it is going to get burned up in the furnace anyway.

By the way, I double-checked.
1) They really do face east (intake) and west (exhaust). I generally
think of the wind as coming primarily from the NW in my area, but I
guess it does come from E or SE about half the time.


You could check with the National Weather Service; they keep records of that
sort of thing.

2) The pipes are about 1 foot above the ground, not 2.5. Maybe the
intake doesn't face down for fear of a drift forming beneath it.


I'm sure that's the reason. It shouldn't be too hard to extend the pipe
upward, though, then put two elbows on it so the opening faces down but is
much higher above the ground.


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MNRebecca wrote:

Another question. Is it possible the builder/installer (furnace went
in during a major house renovation) made the intake pipe face east
(instead of down) to achieve a 180 degree variance with the exhaust
pipe? They're only a few inches apart. If I add some pipe and change
the intake direction from east to straight down, it'll only be 90
degrees different from the exhaust pipe opening. Have I just greatly
increased my likelihood of carbon monoxide poisoning (from the intake
pipe sucking in exhaust) or doesn't it matter much since it's only
going to get burned up in the furnace anyway?


First, there should be little to no CO in the exhaust unless the
furnace is defective. If the heat exchanger leaks, the intake air will
not be your problem. When the furnace is operating properly, the
exhaust is high in CO2 and water, and low in Oxygen. So, you have a
higher probability of sucking water into the intake, where it will
condense and freeze.

You might ask your gas company repair department what the code says
about this type of furnace. I suspect the installation is not up to
code, or is marginal.


By the way, I double-checked.
1) They really do face east (intake) and west (exhaust). I generally
think of the wind as coming primarily from the NW in my area, but I
guess it does come from E or SE about half the time.
2) The pipes are about 1 foot above the ground, not 2.5. Maybe the
intake doesn't face down for fear of a drift forming beneath it.


At that level a drift could cover either pipe regardless of
orientation...
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In article ,
MNRebecca wrote:
Another question. Is it possible the builder/installer (furnace went
in during a major house renovation) made the intake pipe face east
(instead of down) to achieve a 180 degree variance with the exhaust
pipe? They're only a few inches apart.


Unless the horizontal pipes are of significant length (say at least
two feet each), which direction they're pointing is not going to
matter much. In still air, some of the exhaust will get sucked into
the intake. Same if you have a breeze from the west.

If I add some pipe and change
the intake direction from east to straight down, it'll only be 90
degrees different from the exhaust pipe opening. Have I just greatly
increased my likelihood of carbon monoxide poisoning (from the intake
pipe sucking in exhaust) or doesn't it matter much since it's only
going to get burned up in the furnace anyway?


An elbow pointing down shouldn't make much difference; if you're worried
splice in a few feet of pipe to extend the horizontal separation, then
the elbow.

By the way, I double-checked.
1) They really do face east (intake) and west (exhaust). I generally
think of the wind as coming primarily from the NW in my area, but I
guess it does come from E or SE about half the time.
2) The pipes are about 1 foot above the ground, not 2.5. Maybe the
intake doesn't face down for fear of a drift forming beneath it.


There's not much difference if you only add an elbow, and it'd be
easier to clear a drift out from under it than to clean ice out of
the intake.

And, I concur with the recommendation that you should have a carbon
monoxide detector. For that matter, two wouldn't hurt--they're a lot
cheaper than a funeral. I've had them for years (I have gas convection
wall heaters).


Gary

--
Gary Heston http://www.thebreastcancersite.com/

"It's kind of hard to rally 'round a math class."
Paul "Bear" Bryant
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The extra elbows and extenders...they're not going to make it too hard
for the furnace to get air through the intake pipe, are they?
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MNRebecca wrote:
The extra elbows and extenders...they're not going to make it too hard
for the furnace to get air through the intake pipe, are they?


A couple elbows shouldn't matter unless you have a lot of piping getting there.

On my house, the intake pipe comes out of the wall , with a downward facing
elbow to prevent water/dirt entry. The exhaust pipe has 2 elbows so it jogs
down, then points straight out from the wall so the exhaust is directed away
from the house and intake. A short length of pipe on the downward jog can be
used to keep it from hitting plants that might be damaged.

CO should not be an issue. If some exhaust gets drawn into the intake, it will
just go through the burner and right back out. It won't stay in the house.


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On Feb 10, 10:43*am, "Bob F" wrote:

A couple elbows shouldn't matter unless you have a lot of piping getting there.


Like 12 to 14 feet? The furnace is not against an external wall.
It's in an interior room surrounded by a basement addition. The
intake and exhaust pipes run about a dozen feet or so across the
basement ceiling before breaking through an external wall. Still okay
to add some extension and a few elbows outside?


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In article , MNRebecca wrote:
On Feb 10, 10:43=A0am, "Bob F" wrote:

A couple elbows shouldn't matter unless you have a lot of piping getting =

there.

Like 12 to 14 feet? The furnace is not against an external wall.
It's in an interior room surrounded by a basement addition. The
intake and exhaust pipes run about a dozen feet or so across the
basement ceiling before breaking through an external wall. Still okay
to add some extension and a few elbows outside?


If you're really concerned about that, add an adapter just outside to
transition to the next larger size of pipe, and make the extensions and elbows
in the larger size.
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MNRebecca wrote:
On Feb 10, 10:43 am, "Bob F" wrote:

A couple elbows shouldn't matter unless you have a lot of piping
getting there.


Like 12 to 14 feet? The furnace is not against an external wall.
It's in an interior room surrounded by a basement addition. The
intake and exhaust pipes run about a dozen feet or so across the
basement ceiling before breaking through an external wall. Still okay
to add some extension and a few elbows outside?


That sounds very similar to mine.

You might be getting close to the limits. Reading the installation manual for
your furnace should give you the necessary info. I managed to get these for two
used furnaces by contacting the manufacturer. In one case, I had to talk to a
distributer in the end to get it. The other was easily downloaded.

You shouldn't need to add many elbows. At most, 2 on the exhaust outside, and
probably 1 on the intake should be all you need.

You could try just pressing the elbows on and see how it works. The furnace has
sensors that cause it to shut down if things aren't right. But don't go much
over waht the manual says.


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In article ,
MNRebecca wrote:
The extra elbows and extenders...they're not going to make it too hard
for the furnace to get air through the intake pipe, are they?


I doubt it. You should have an owners' manual or some technical material
for your furnace (or look it up by searching for the model number). That
should have some information on the maximum intake/exhaust piping and
what diameter it should be.


Gary

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Gary Heston http://www.thebreastcancersite.com/

"It's kind of hard to rally 'round a math class."
Paul "Bear" Bryant
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MNRebecca wrote:

The extra elbows and extenders...they're not going to make it too hard
for the furnace to get air through the intake pipe, are they?


In general, no. However, check with your gas company or the
installation docs for the furnace. There may be stated limits or codes
that govern.
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I had a new furnace installed in 2012 and deal with this several time every winter when it gets below zero! My furnace guy has adjusted my pipes a few times, but he just says there's nothing you can do with these outdoor intake pipes. There has to be something!!! There was some good advice here.

n Tuesday, February 2, 2010 at 4:22:41 PM UTC-6, MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.




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In

MNRebecca wrote:

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.


The intake pipe on our furnace points DOWN; the exhaust is parallel to
the ground, like yours seems to be.

We've had a high-efficiency furnace with PVC intake and exhaust like
yours for more than 20 years and have never had a problem with snow
blocking the intake. We'll have icicles hanging from the exhaust, but
they don't block the pipe.

--
St. Paul, MN
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Default How to avoid ice-clogged furnace air intake pipe?

wrote:
I had a new furnace installed in 2012 and deal with this several time
every winter when it gets below zero! My furnace guy has adjusted my
pipes a few times, but he just says there's nothing you can do with
these outdoor intake pipes. There has to be something!!! There was
some good advice here.

n Tuesday, February 2, 2010 at 4:22:41 PM UTC-6, MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm
told, by the repair guy, is harmless), it fires back up and runs
fine. But I hate the idea that, each year, I have to live in dread
of the time I'll wake up in the middle of the night to a
disturbingly cold house and then have to live with a furnace drawing
air from a basement room instead of outside (until temps outside
climb above freezing, which can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks
so much if you can help.


Concentric pipes, with the exhaust air pipe outside of the intake pipe would
warm the intake pipe so freezing could not occur. The trick would be how to
properly direct the exhaust air away from the intake inlet. Perhaps a "T"
fitting for the exhaust around the intake pipe, with the exhaust directed out at
a right angle away from the inlet.


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Default How to avoid ice-clogged furnace air intake pipe?

On Tuesday, February 2, 2010 at 3:22:41 PM UTC-7, MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.


The exhaust should rise up 18 inches and face out with a 90 directly away from the building. This will prevent cross contamination of the exhaust gases with the return air supply to your appliance. This should reduce the likelihood of recurring events but it may not eliminate it entirely. I read about a new product which is supposed to prevent the ice or frost at the vents by a company called Frostfree venting. Their product may solve your issue.
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Default How to avoid ice-clogged furnace air intake pipe?

On Tuesday, February 2, 2010 at 5:22:41 PM UTC-5, MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.


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Default How to avoid ice-clogged furnace air intake pipe?

On Tuesday, February 2, 2010 at 5:22:41 PM UTC-5, MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.


Just had frost-clogged intake caused by moisture from exhaust blowing by intake pipe and freezing on insect screen. I put a 45 degree elbow on the exhaust to divert it further from intake and attached a wooden 20 x 20 inch divider to the house to help keep moisture from intake. Works fine. Temp was below zero and windy.


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I'm in Minnesnowda and I have this problem too with my roof top pvc intake and exhaust. The exhaust has an 180 elbow which tends to blow right toward the straight up intake.

Toward the end of last winter I read this thread and got an 180 elbow to put on the intake, but just today (1st sub zero temp of the season) the intake frosted over again. I cleared and changed both elbows to face more directly east for exhaust and west for intake. But I'm wondering if the exhaust needs to have an elbow at all. Wouldn't it be better if it just blew straight up and let the wind take it from there?
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Default How to avoid ice-clogged furnace air intake pipe?

On Saturday, December 10, 2016 at 3:28:11 PM UTC-6, Bob F wrote:

The elbow probably keeps rain/crud from going down the pipe and damaging
the furnace or overworking the condensate pump.


You're probably right. I'm hoping re-positioning the direction of the pipes will help. I'll be taking off for the holidays and it will be bad news if it frosts over while gone.

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I have the same problem, luckily i have one of those wifi thermostats and the furnace sends an email when there is an alarm, on my lennox the alarm mentins something about a rollout switch whenever the intake is clogged? This last time i was in Hawaii and it was -32 C in Edmonton when i got the email, it really is a handy feature, ata minimum even with an older furnace you can at least check the temp from anywhere, i think i will try some of the recommendations in this thread with adding a divider or modifying piping, my intake points down but sits right between the hwt exhaust and durnace exhaust, i am sure that humidity is causing the intake buildup
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I believe the problem of frost build up occuring, is from a warmer intake vent temperature and extremely cold air drawn together. Not unlike the frost in a poorly sealed freezer or on old windows. When the colder outside air is drawn into the vent pipe, upon mixing with the warmer air radiating within the pipe the moisture from the cold air converts to frost. The solution may be to create a trap, limiting warm air from moving out through the pipe.. Something as simple as a damper or flapper type of trap. Exhaust fans have a flapper to only allow air out, and doing this in the reverse may be the easiest fix. The furnace shuts down when the intake is restricted, because it has a pressure switch in the combustion box that senses vaccume pressure. Any flapper or damper would have to be opened easily and fully by the combustion fan..


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There are dampers available for furnace air intake vents and are relatively inexpensive, but are controlled electrically and may require a technician to install. Also this may not entirely solve the problem, especially when the outside air temperature is below zero. But will lessen the occurrence of frost build up.
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On Thursday, January 26, 2017 at 7:51:13 AM UTC-5, wrote:
There are dampers available for furnace air intake vents and are relatively inexpensive, but are controlled electrically and may require a technician to install. Also this may not entirely solve the problem, especially when the outside air temperature is below zero. But will lessen the occurrence of frost build up.


My high efficiency furnace uses a concentric vent pipe for exhaust/intake.
Issues started happening January 2018 when it got very cold.

Short heating cycles on 2nd stage heat that were not heating up the house fast enough.

My furnace is new and under warranty. The technician came today and found that the gas pressure was too high and the safety switch was shutting down the furnace due to excessive heat.

He adjusted the gas pressure valve and it seems to be working right now.
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I live in Manitoba and have the same issue. When I asked the technician about the exhaust and intake pipes (by the way, mine are not separate outside but are joined together just before exiting the foundation - should I be concerned about that?) and the slope of them, he brushed it off. After he left, second time, I went outside and I could actually look down into the pipe and see water droplets. I pushed the outside vent back on as it was barely attached and the furnace cut in and has been running fine since then. The guy never went outside to have a look. Just spent 2 hours running checks and looking for code issues and kept telling me the furnace was working even though the temp in the house was 17 and the thermostat was set at 21. I suspect I need to attach that exterior vent better but should I also replace it with 2 separate vents?
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I've had this problem as well. It's generally not 'water' freezing in the intake pipe, it's due more to the fact your intake and exhaust ducts ate too close together, the exhaust releases warm exhaust with condensate (warm moist gases), which are drawn to the nearby intake. The problem is exacerbated if your intake vent/pipe has a mesh screen, (wire or pvc
mesh) used to keep debris or critters out of the pipe. The mesh creates more surface area, increases cooling and frost build up. Other internet experts recommend adding 90 degree bends or extensions to the pipe, but they don't say that each bend or extention increases distance, and resistance to airflow which can overwork your draft inducer, shortening it's life and decreasing efficiency.
I solved my problem by installing a 2 inch to 4 inch pvc pipe transition, I used 1/2 inch chicken wire as a critter shield, then painted it flat black. The system works, the flat black paint absorbs solar radiation adding just enough heat to stop frosting over. It was -30 degrees last winter and it never frosted over.
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