PVC furnace exhaust freezes

I have a new gas forced air furnace, Amana. The PVC exhaust runs about horizontally 30 feet to the outside wall. PVC makes a slight pitch back toward the furnace for draining. Everything has worked fine until the temperature outside dropped into the single digits. (Upstate NY) The furnace will not come on until I go out and clean out the ice formation on the end of the pipe. Now there is not a lot of ice, only a ridge around the edge. What do you suggest I do to stop this? Should I insulate the pipe so it doesn’t freeze? Or should I change the pitch so more moisture drains back instead of out? The shape of the pipes looks like rams horns, 2 pipes up about 3 feet 12 inches apart. Then to 180 degree fittings on top dump down opposite each other. Should I change the outside configuration?
Thanks TP
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Call the installer
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On Sat, 22 Jan 2005 00:18:43 GMT, TP

Read the installation instructions for the terminations of your pvc pipes. They are very specific as to how they are to be run. Each manufacturer has a slightly different idea on how this gets accomplished. Bubba
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What size PVC is it? It maybe too small for the 30 foot run. You have to count the number of elbows also. Check the manual. I'd call the installer even if this appears to be the problem.

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Thanks, the installer retired. I have checked the manual and the pipe dia and length are fine. I took a shop vacuum to both pipes, just to be sure. Now the problem has seen to gone away. The only thing that I noticed was there was not a screen on the intake pipe. The manual doesn't specific any size of screen, but shows a picture of one. Could I use standard window screen? Or something heavier gage?
TP
Jeff Guay wrote:

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If your PVC pipes (inlet and exhaust) do not have any kind of screening at the outside ends you are looking for trouble. Those open pipes are quite attractive to various animals who would just love to make a home inside one of them. After one tried, even chewed through some plastic ribs across one of them, I covered the opening with some chicken wire to keep them out. MLD
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Go out and watch the operation of the exhaust pipe for awhile...and, especially on a windy day. A common problem is the exhaust dumps back on the intake pipe opening and the exhaust condensate/vapor freezes up the intake. If this is happening, then, you need to redirect the exhaust and/or change the intake to a more suitable position . This can often be done by having the exhaust blow outward from the house at a higher level than the intake pipe is , and, at 45 degrees to the house wall for maximum distance from the intake. Refer to your furnace instructions first.
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Is this the original 'TP'?
Tom?
~kjpro~
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I'd suggest hardware cloth, with the 1/2" mesh.
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I have a similar problem you mention here. I forced my installer to add a screen. I will post a pic here, after my camera batteries are recharge.

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wrote:

No don't, as this is not a binaries group!
Which means, no pictures!
E-mail them to the party that wants them instead!
Thank You,
~kjpro~
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OK, no pic and I don't E-mail either. Sorry.

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That's OK about the picture. I understand you shouldn't screen the exhaust, because it could freeze up. I like the idea (DN B) of raising the intake pipe. The manual shows that as an alternative method. What I have done today is made a 6 inch length of foam insulated pipe. Extended these to both the intake and exhaust. Seems to working. I did notice in the basement the intake pipe drips with condensation. Could this be the source of the problem? Water going into the intake....
TP
Jim B wrote:

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It is impossible for me to explain it, except post the pic. This PVC adaptor screen solved all my problems. I believe you could get this PVC adaptor screen in Home center.

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add a

recharge.
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Check these pictures out....
http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID#286&mc 

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Thanks. I don't have ice like those pics. There one that’s really built up, like water was running… I don't understand all the screen issues? My ice is just at the end of the 2 inch pvc, it forms a small ridge. I’m guessing this ice is not my major malfunction... I feel the moisture could be related to a prox switch going bad. If when the furnace will not light, I unplug the rubber hoses to the 2 prox switches of course power is off. Apply vacuum to click the switch. Plug them back in. Power back on to reset. All is well for a day or less….
TP
== HeatMan wrote:

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On Mon, 24 Jan 2005 01:58:23 GMT, TP

So you think pulling the rubber hoses off the pressure switches and sucking on them is the way to make your furnace work every day or two? Could you please post your owners operation manual on that furnace because Ive never seen those kind instructions anywhere. Bubba

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Ha Ha .. thanks Bubba. just to add another twist... if I leave the access door on the front of the furnace open a little( so it takes in some air from basement) the furnace will run with no problems. Does this prove that it is a moisture condensation issue with the sensors being sensitive to moist intake air?
TP
Bubba wrote:

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hehe. No, it proves that you most likely have an intake and possibly exhaust piping error. Read the installation manual and do it BY THE BOOK or call someone that can. Oh yeah, one other little twist, since you are dealing with the combustion air of the furnace and possibly the exhaust gasses of the furnace, you might want to leave it alone since these items incorrectly serviced can kill you and your entire family and you wont even know it. Bubba
On Mon, 24 Jan 2005 22:57:52 GMT, TP

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