frost buildup on furnace intake

Ok, for the past couple years I've had intermittant blockages in my gas fired forced air furnace intake due to frost buildup (apparently, called hoar frost). It tends to happen on cold, high humidity days with little or no wind. Looking at the venting setup at my house in the arctic tundra of western NY, I see my hot water heater vent (6" PVC) is furthest west (on the south side of the house), the vent from the furnace (3" PVC) just several inches away, then the furnace intake (3" PVC with a vertical extension about 1 foot up) only a few inches away from that. So, two vents upwind of the intake. Short of redirecting the intake to be further away (would presume 1 - 3 feet from Google searches), is there anything else I can do to prevent this? I realize, I can just go out and clear the frost periodically (jam something up there). I've also read about electrical heat tape but worry about the safety. I even thought about coating the inside of the PVC with something that would deter frost formation, or painting the PVC black so the sun would melt the frost quicker...
Any ideas? Thanks, Earl
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Your saying the intake is above the exhaust for the furnace and water heater?
If so, what is the make, model of the furnace?
And what type of water heater do you have that requires a 6" PVC pipe?
~kjpro~
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No, not "above", just upwind. They are all about the same height. Water heater is an AO Smith powervent. I don't have the manual for the (Luxaire, don't have the model number on me right now) furnace - I'm going to try and get ahold of it though.

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Read the installation instructions for the furnace and water heater. They both will have guides and even diagrams of how to vent them properly. Bubba
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