Intake/Outtake freezing up

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  #1  
Old 12-24-04, 09:35 AM
pherzog
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Intake/Outtake freezing up

It's -10 in Minnesota today and my outdoor intake/outake is freezing up on my furnace/air exchange. This causes the furnace to shut down. It also leaves a pile of ice below the outake every year.

Can I get a list of things to check?
 
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Old 12-24-04, 12:30 PM
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Yes, we've been having a good cold blast here in MN.

You are going to get some ice dripping off the exhaust pipe from the furnace. I only got about 5" hanging.

If your is pretty big and thick, check to make sure the exhaust pipe is pitched back toward the furnace. (about 1/4" pitch). If it's not the water that is in the PVC exhaust is going to roll outside.

How are the pipes set up together on the side of the house?

The intake should be pointed down towards the ground, and the exhuast should come up about a foot, and 90degree out.
 
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Old 12-24-04, 02:48 PM
pherzog
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Our intake/exhaust is directly under our deck attached to the second level. It comes straight out from the house, no angles. The exhaust cloud was hitting the outter frame board of the deck and flowing back towards the intake. So, this morning we drilled a hole in the outer board and extended the pipe so that the exhaust blows out past the deck. We sloped the pipe down from the house. We aren't as concerned about the pile of ice as we are about the pipes shutting down the furnace.

The intake comes out 2 feet alongside the exhaust with a PVC elbow pointing to the ground.

Did I understand you when you say the exhaust should slope towards the house so that the moisture flows towards the house? I am concerned that would plug it up with ice.

Merry Christmas by the way!
 
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Old 12-24-04, 11:12 PM
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Condensing furnace venting needs to be pitched back to the furnace. This allows the condensation in the vent piping to flow back to the furnace and out through the furnace drain. If the vent piping is pitched to the outdoors, that will aggravate the ice problem.

Outdoor (or pipe in an unconditioned space) sections of pipe need to be kept to a minimum. If the lengths are too long, they need to be insulated with Armaflex.

Some manufacturers recommend a 3x2 reducing coupling on the exhaust pipe to increase the velocity of the exhaust. This increased velocity moves the wet exhaust vapors away from the cold intake pipe where they freeze.

The exhaust termination needs to be a minimum of one foot above the intake pipe. There are also mimimum clearances to the house, eaves, windows, etc.

I have always installed a simple test tee and plug in the intake pipe at the furnace. If the intake freezes outside, remove the plug and the furnace will work (just to be perfectly clear, NEVER do this on the exhaust pipe). That is much easier than cutting off the ouside terminations.... Sometimes weather conditions are so bad that even a textbook perfect exterior vent job will freeze up.

I also never glue the exterior terminations to the pipe installed through the house. The assemblies (elbows and such) are glued together, but they are easily removed. Simple friction or silicone caulk works fine.
 
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Old 12-26-04, 07:48 AM
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yes, the ideal thing is have the exhaust pipe pitched towards the furnace. But if you have alot of space between the exhaust and ground where the ice builds up, then it's up to you.

How much is this exhuast pipe itself exposed to the outside air? If you have too much, the water in it may freeze up if too much is exposed.
 
 

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