I feel your pain, we had a similar install that wasn't ideal, in a tight breezeway beside our practically new (2012) home, that would operate fine... until the cold snap when you actually need it (at which point exhaust would recirc into the intake and freeze up on the screen). In our case it was a separate 3" ABS intake (elbowed down) and 3" CPVC exhaust (which elbowed up, but then had a gooseneck at the top so it blew down) for a boiler. Might have met code (haven't checked in a while), but the downwards pointed exhaust definitely doesn't meet the boiler installation requirements (which could have voided the warranty if it failed and was found in that state), and a little surprising that a new system in a new home, that would have required a decent plumber to do the rest of the hydronic system, would miss something like this.
Looking at your picture, I'm assuming the following but can you confirm (if looking at the picture correct side up)
1) Sheet metal duct at the lower left is your fresh air intake for the HVAC system? (could also be a fresh air intake directly into your furnace room too, but judging by the 2 pipes to the right of this you have a direct vent furnace, so this would not be necessary unless you have a naturally vented HW tank in the same room)
2) The middle pipe (elbowed up out of the wall, then goosenecked back down), just to the right of your hose bib, is the combustion air intake for your furnace.
3) The pipe on the furthest right is your furnace exhaust.
4) It's the 2" PVC air intake that's freezing up that's causing the issue? (I can see a little bit of freezing on the sheet metal intake, but again if this is your fresh air intake that's not ideal but it's also less of a concern.)
Assuming the above is correct and it's the 2" PVC that's freezing up, the main issue that causes the freezing is warm moist furnace exhaust being recirculated into the intake. The one issue I see with your install is that usually the furnace installation manuals call for the exhaust (furthest right) to be 12-18" higher than the intake. In your case, they also elbowed the intake up to bring it higher, which brings it to almost the same elevation. It's hard to tell from the picture, but they may have done so if they felt that coming out horizontally from the wall and elbowing downward right away made it too low. Again, please confirm the above questions, but if all that is correct, the two fixes that I would see are below.
1) Move the furnace air intake lower. The easiest way to do so, if you have the room, is to cut the straight pipe where in intake comes out of the wall, as close as possible to where it elbows up, as long as that still leaves you at least 1" or more of pipe coming out of the wall, so that after cutting you have room to attach an elbow pointing downwards. Hopefully this would bring the intake low enough that it no longer ingests any moist exhaust air to freeze up on the intake.
2) Move the furnace exhaust higher. But, this may not meet the requirements of the furnace install, and you will also have to check clearances to all of the surrounding openings if you're moving the exhaust. To me this is less ideal, as it also creates more surface area of exterior piping that has warm moist air blowing through it periodically and can freeze up on the interior of the pipe in between heating cycles.
Hopefully CaberTosser and/or some other plumbers will pipe up as well to confirm my suspicions, or call me crazy.
|