Ask Me Help Desk - Freezing/icing at outside vent

Freezing/icing at outside vent

I have a plus 90 bryant furnace, vented out on north side of home, installed about 4 or 5 years old, when temp gets down around zero and some wind, usually, the vent will ice up and furnace will not come on? When I take vent cover in and thaw the ice off it, then furnace will come on?

Vent cover? Screens or strainers on the vent terminations are not recommended as they can frost over in cold weather. Check to assure the exhaust vapor is not returning to the intake.

Quote:

Originally Posted by KC13

Vent cover? Screens or strainers on the vent terminations are not recommended as they can frost over in cold weather. Check to assure the exhaust vapor is not returning to the intake.

I gave my time to address this issue; while possibly inaccurate, I did not give you "bad advice". If what you are referring to is a concentric vent termination, a better description on your part may have netted a more accurate suggestion on my part. Remember, I am not there to see what you are referring to, but I am attempting to help you nonetheless. The condition you described is usually caused by screens or perforated discs installed in the terminations. Next time, I would suggest a little more effort and research on your part before casually stamping a blemish on someone's reputation.

More inducer vent pipe icing...

I'm having the same issue (Toledo, Ohio) and it's around one (1) degree outside. This is my third (3rd) winter in this house, and the first time I've encountered this problem.

My 3" PVC intake & exhaust are open-ended (no covers or screens) and the intake is building up frost crystals (soft, not like solid ice) to the point of blocking the port.

I've "reamed" it out twice tonight, the last just before going to bed (where I'm posting this), I'm hoping that I don't awake to a freezing house...

Any help or insight will be greatly appreciated!

Randy Forbes

Several possibilities: we'll throw out the screens/discs... the terminations may not be spaced far enough apart. Typically the intake turns down and the exhaust turns outward. Ideally they should be spaced 10-12 inches apart and at least 8 inches above grade or anticipated snowline, whichever is greater. Some thoughtful installers will refrain from gluing the last fitting on the exhaust termination to allow it to be turned if necessary. Check for exhaust vapor entering intake - this is a no-no. The installation manual will give the specifics for venting this unit.

Quote:

Originally Posted by KC13

Several possibilities: we'll throw out the screens/discs...the terminations may not be spaced far enough apart. Typically the intake turns down and the exhaust turns outward. Ideally they should be spaced 10-12 inches apart and at least 8 inches above grade or anticipated snowline, whichever is greater. Some thoughtful installers will refrain from gluing the last fitting on the exhaust termination to allow it to be turned if necessary. Check for exhaust vapor entering intake - this is a no-no. The installation manual will give the specifics for venting this unit.

Thanks!

All the installation criteria you state appears to be met (ducts exiting basement wall at extremes of joist spacing, height, etc.).

Both pipes terminated with 45-degree elbows, each turned outward from the other at a 45-degree angle to the ground.

Woke up with house temperature at 67 degrees; checked the L.E.D.s and found two-blinks, indicating the pressure swsitch open. I'm about to go out and clear any buildup of snow away from the area, just in case...

Any other ideas?

Thanks again.

Randy

Quote:

Originally Posted by Randy Forbes

Thanks!

All the installation criteria you state appears to be met (ducts exiting basement wall at extremes of joist spacing, height, etc.).

Both pipes terminated with 45-degree elbows, each turned outward from the other at a 45-degree angle to the ground.

Woke up with house temperature at 67 degrees; checked the L.E.D.s and found two-blinks, indicating the pressure swsitch open. I'm about to go out and clear any buildup of snow away from the area, just in case...

Any other ideas?

Thanks again.

Randy

No major buildup, just about 2-3" of hard-hard snow (might as well call it ice) on the mulch. Without accurate measuring, I'd say the pipes are 14" above the finished grade (top of shallow layer of__frozen__mulch).

As a temporary measure, I've left the combustion air alternate side entrance cap off the unit (the pipes are connected running straight up). I realize this will draw air from the house, but at 2600 sqft (not counting unfinished basement). The exhaust is still ducted to the outside.

I won't rule out that a small animal has gotten in, but it could only have been a bird, based on the distance to the ground.

What about a bit of electric heat-trace around the combustion air inlet? Given our similar locations, you know what the temperature here (in Toledo) is like last night/today.

Without accurate measuring, I'd say the pipes are 14" above the finished grade

I believe the snow line in Toledo is above 14 inches. Look at the manual to check but I believe the pipes will need to be moved higher.

Consult the installation manual. The spacing at the terminations is important - not only horizontally, but vertically as well. Typically the exhaust terminates higher than the intake to reduce the chance of vapor re-entering the intake. It sounds as if this is not the case with yours.