I have a high efficiency furnace that exhausts via a pvc pipe out the side of the house, the trouble is the moisture from the exhaust forms an ice stalagmite in my driveway in the cold weather.

Are there ways to prevent this ice from building up (other than throwing salt on it twice a day)?

  • Is the vent very exposed to the elements, such as sticking out just along an exterior wall, with no corners nearby? What may be helping the freezing is wind blowing by the exhaust pipe, lowering the air temperature nearby enough to freeze it quickly. If this is the case, and a small windbreak was constructed, perhaps it would help. – trip0d199 Feb 9 '11 at 14:38
  • @trip0d199 - Not sure a windbreak will help when the temperature is below freezing (without the wind). the ice is forming on the ground creating a stalagmite not from the pipe forming a stalactite. – Tester101 Feb 9 '11 at 14:50

Attempt No.1

  • Acquire small plastic container.
  • Drill small holes around base to allow water to flow out.
  • Fill with salt.
  • Place under exhaust vent.
  • Wait and see what happens.

I'm hoping the moisture in the exhaust will drip into the container of salt, and then run out carrying salt with it. This might have the added benefit of dispersing salt to the nearby area, thereby preventing snow and ice from forming in the vicinity.

The down side is that instead of an ice stalagmite, I will have a plastic bucket in the driveway which will get in the way while shoveling/snow blowing.

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btw I have the same issue on my HE home furnace. and just by chance, the billing department manager at the furnace company I use has the same problem.

I did see an online article which mentioned some solutions. NOTE that exhaust pipe condensate drainage is the first thing I noticed appropriate to my problem.

If you experience a shut-down of your high efficiency furnace and suspect it’s related to a venting issue, check for these common venting problems:

Incorrect sizing of the exhaust pipe. Manufacturers specify the maximum length and number of elbows that pipe of a given diameter can have. And most high efficiency furnaces require 3″ diameter pipe. If you’re not sure check the furnace’s installation manual (if available) or contact the installing contractor to verify the pipe is sized correctly.

Not enough hangers (or straps) to support the exhaust pipe. If sags develop in the exhaust pipe, condensate moisture will pool in the low spots, creating enough blockage in the vent to trigger a shut-down. This is especially true during colder weather, where longer run times produce more condensate moisture.

Incorrect slope of the exhaust pipe; sloping downwards towards the outdoors (on sidewall vented furnaces). This pipe must slope back towards the furnace approximately 1/4″ per foot, allowing condensate to drain freely back into the furnace.

Vent terminations positioned too close to the ground. Show drifts or accumulations can block the vent, or ice buildup (see photo) can reach the vent and create a blockage.

Having the intake and exhaust vents installed on different sides of the home. The pipes MUST be terminated on the same side of the house, in close proximity to one another, so that the wind pressure is the same on both pipes.

Birds, insects or other critters have made their way into the vent. I’ve run across this problem many times. Unfortunately there’s not much that can be done to prevent this from happening, and removing these uninvited guests should be done by a qualified hvac technician....'

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If the distance isn't too far from a non-driveway patch, you could put a chain from the drip point and anchored somewhere off the driveway. That way, water will run down the chain and either freeze there or freeze where ever it is anchored.

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  • Not applicable to my situation. But could be a viable solution if it was not too cold and the run was not too long, otherwise you would just end up with an icy chain (and probably icicles hanging from the chain). – Tester101 Feb 9 '11 at 15:32
  • @Tester101 the chain does end up icy, yes, but the water tension of the drips should allow them to continue to flow along chain and eliminate icicles. A shame that it wont work for you. – Bob Roberts Feb 9 '11 at 16:10

If the cool down the exhaust gasses more you will reduce the level on condensation that is build up on the end of the exhaust pipe.

The heat exchange in the furnace may not be working as very well as possible due to not having enough air being blown over it. (With water based systems it is often due to have the boiler set to high, so stopping the boiler condensing.)

Also consider getting a Gas-Saver fixed, this will preheat the water free for you hot water, so saving gas as well the cooling the exhaust so condensing out more water before it gets to your exhaust pipe.

enter image description here

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Consider insulating the exhaust pipe. If the exhaust is cooling off before exiting the pipe then water will condense out of it more readily, if the exhaust is still warm as it exits the pipe then any ice that does form will ultimately be melted.

It may be that you only need wrap the exterior portion of the exhaust pipe, keeping the last inch or two of pipe free of insulation, but if that doesn't resolve the problem you may consider wrapping some of the interior portion so the exhaust retains its heat all the way to the exit.

If that doesn't resolve the problem, then a short length of heating tape wrapped around the exterior of the pipe then insulated should prevent ice formation. Perhaps just a small length wrapped around the very end of the pipe would be sufficient.

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Attempt No. 2

  • Acquire womens pantyhose/stocking.
  • Fill partially with salt.
  • Affix salt filled pantyhose/stocking to exhaust pipe using zip-tie.
  • Wait to see what happens.

With this attempt the moister in the exhaust should still disperse salt to the nearby area, however, it eliminates the pesky bucket from the driveway.

The down side here could be the pantyhose/stocking does not allow the exhaust to escape effectively, causing toxic gases to back up into the house harming and/or killing all occupants (but that's why it's attempt 2 and not attempt 1).

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  • 1
    When I saw 'Acquire womens pantyhose' the first thing I thought was "How is robbing a bank with pantyhose on your head going to prevent ice buildup?" :) – Doresoom Feb 9 '11 at 17:20
  • 1
    @Doresoom - because then you can buy a new house someplace warm, and you don't have to worry about it anymore. – Tester101 Feb 9 '11 at 17:23

Attempt No. 3 (The hybrid)

  • Acquire J hook or eye bolt.
  • Install J hook/eye bolt above exhaust pipe.
  • Acquire plastic container.
  • Drill small holes around base to allow water to flow out.
  • Fill container with salt.
  • Affix string/steel cable/bungee to container to create a handle.
  • Hang contraption from J hook/eye bolt.
  • Wait to see what happens.

This approach combines both attempts 1 & 2 to create a hybrid system that should alleviate the drawbacks of each system. It eliminates the annoying bucket on the driveway, and should allow exhaust gases to flow normally. It should also have the benefit of the other systems, and disperse salt to the nearby area.

Down side unknown.

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