Furnace help (venting)
 

Obviously this shouldn’t be happening. We’ve always had to clean up the intake due to frost build up. Never gave much thought to it. It was only done once or twice a season, some years never at all. However due the the extended cold snap we are in, we’re clearing it once a week. It’s dangerous, furnace quits, carbon monoxide is also a risk.

Is it as simple as changing angle of the intake (adding a 90 degree piece) or are there location issues?

The furnace was installed 6 years ago.

I had problems with my furnace twice so far during the -30 weather due to frosted up vents. Your vents are nothing compared to what mine were like. The exhaust vent had a frostcicle sticking out about 3 inches and there was only about a 1" gap left for the exhaust to escape. Once I cleared that the furnace worked fine. I currently have one panel off of my furnace so it'll work. I think that the intake vent started to get plugged up and it couldn't get enough air. New high efficiency furnace installed in 2013.

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.

Yes, the intake gets plugged and the furnace quits. It is a relatively common problem and that is why I've never worried about it too much, especially once or twice a season, but our furnace is quitting once a week in this cold weather.

We have to constantly keep an eye on it to ensure it doesn't plug up. I'm hoping it is a simple solution vs re-routing venting etc.

Yup, and what happens when you want to go on vacation or away for a weekend...

Again, please confirm the exact questions/description above, but if my above description of your system is correct and it's the 2" PVC on the left which is your air intake and is freezing up, cutting the pipe at lower level where it first comes out of the wall horizontally, and attaching an elbow so the intake faces downwards, is a very easy fix. This would be simple enough to do yourself, will take about 15 minutes and cost less than $5 for the elbow, and you can even just pressure fit the elbow until you confirm it fixes the problem (the glue isn't absolutely necessary as it's only conveying fresh air, but is again required by your install manual so you should eventually glue it). If there isn't enough length of straight pipe left where the intake comes out of the wall to cut and fit an elbow, another option would be to cut a section out of the vertical pipe on the air intake, then just reinstall the same gooseneck (using a coupling fitting), to bring the air intake vertically lower that way. Either of these are not a major re-route at all but if you're not comfortable doing this yourself, definitely hire a qualified furnace / HVAC tech.

You can and should look up the installation manual for your exact furnace model yourself, to look at the recommended air intake configuration, but of the many configurations shown in the manuals, most of them have some vertical separation. Bottom line, in our climate with these extreme cold snaps, you ideally want some vertical separation between the intake and exhaust to help keep the boiler/furnace/HW tank from ingesting it's own flue products i.e. warm moist air (with intake pointed down, and exhaust pointed outwards or even some angle up). Your original questions of changing the angle of the air intake by adding an elbow (so now it will be pointed outwards?) is the same amount of work as what I've suggested and will likely not help the situation, as it will still be at the same height and very close proximity to the exhaust.

The acceptable "venting configurations" page in most furnace manuals are virtually identical, feel free to look at the bottom of page 42 of the link below for some visuals of the "vertical separation" that I'm referring to.

https://www.utcccs-cdn.com/hvac/docs..._ICP_24220.pdf

The metal duct is likely the dryer vent. It is on mine. The pipe with the 180 degree bend at the end is the intake for the furnace and the pipe sticking straight out is the furnace exhaust. That is the way that it should be. The intake is designed so rain/snow can't block it. The best position for the exhaust is sticking straight out as it is. Any other position and you'll create even worse problems. Don't mess with it.

My furnace doesn't quit entirely when the exhaust frosts up. It continuously cycles warm air so it's not like it's going to get cold enough to freeze pipes.

When I install those for my boiler or water heater installations I place the intake upwind of the exhaust based general prevailing winds so that they have reduced likelihood of re-ingesting moisture from the exhaust stream. I will also point the exhaust to discharge away from the structure and the intake drawing from close to the building. I also try not to have the intake & exhaust placed so close together in the first place. When venting multiple appliances I will gang the intakes together and separate them from the exhausts by 36" or whatever I can achieve given the options available.

One can extend the exhaust a couple of feet (within reason) as they do not tend to frost up because of the heat the blow out. My only issues on service calls have been frosted intakes (these are worse to extend as that gives them more exposure to potential frosting). While I have not personally had calls with frosted exhausts I won't completely negate the potential, given other circumstances possibly at play (its just much less likely). Other factors with exhausts is that they must be graded like a drain to allow condensate to drain back and out the appliance condensate drain. They cannot be level or have a configuration of fittings that create a trap.

I would avoid lowering the intake as CzechM8 suggested, there are ground clearances one wants to maintain to prevent the intake being plugged by a heavy snowfall.

Thanks czechm8....all of your observations are correct. The intake is facing out but immediately drops down. Like a periscope on a sub lol.

As someone mentioned above, we were on vacation for three weeks, got home a week after the cold snap hit. The furnace quit within hours of us coming home. If we were a day or so later, we would have had problems.

The pipe (sorry about the side ways pic/dumb phone) frosts up, usually it is as quick as sticking our hand in there and cleaning it out although last time we has to use a hair dryer, to blow hot air down in the pipe.

I talked to Weiss Johnson (they did the install) and were very helpful. They recommended extending the intake pipe straight out 12-18", parallel to the ground. Sounds like an easy solution although long pipe would be kinda ugly.

I also wonder if changing the outlet too??

If that doesn't work, we'll have to make some changes to the ducting.

The silver vent is the dryer vent.

The pipe that bends down is the exhaust (warm air)

The pipe on the far right (looks like a periscope) is the intake, that is what is freezing up.

Here....a better picture!!

https://i.imgur.com/UwKdaSL.jpg?1

Looks like a pretty poor installation, over the exterior taps. Updated my furnace a couple of months ago. There's a meter high Phallic symbol growing below the outlet. :lol:

Grizz

If that installation was the opposite of what it is, you'd be in much better shape. The exhaust should be blowing away from the structure and the intake should be the one tucked in tight, the opposite of what you have there. It might be easy to revise by switching them over inside at the furnace.

Knocked down my neighbor's for him.

Was 3 feet or more tall.

V

I always thought that the code was to keep intakes 3 feet or so away from exhaust. Just seems wrong that a intake would be that close and able to suck in exhaust gases. JMO .
Would a heat exchanger in side help this problem ? Warm air and pipe cooled before exiting the building and vise versa ?? Just wondering ??

Caber is the person to give input on these things. He knows everything.

This is why contractors who don't spend the extra $30 on the install should be slapped. A contract horizontal termination kit or even a concentric kit solves all of these issues.

https://media.diversitech.com/product_image/HVENT-3.jpg

Those may be OK for a one or two stage furnace that maintain a reasonable exhaust velocity, but for an appliance such as a modulating/condensing boiler that can fire down to 10% of its rated possible output its not ideal, at low fire the exhaust is not blown far and on a windless day a lot of that will get re-ingested and frost up the intake. The best tactic is 36" or more of separation horizontally and a bit vertically too if possible.

This is your problem, the far right one should be the exhaust.

Have your neighbour remove that tee and his problems will be over.