Intake and vent termination

[bnymbill]

Good afternoon,

I came across a situation where the builder mixed up the intake and vent for the furnace, i.e., looking at the diagram in the Goodman manual, it was reversed. So, the intake was 12" above the vent instead of the opposite. I also noticed the water heater vent was way too close to the furnace intake compared with what's specified in the manual and also installed 12" below the furnace intake.

So, my question is, what are the hazards of the furnace intake bringing in combustion gasses along with clean air? They make concentric kits where the vent and intake are together but they're designed to separate the intake and vent.

I'm going to make note of it since the IRC says to follow the manufacturer's instructions but what is the actual hazard of the furnace intake bringing in combustion gasses? Dirty burning causing buildup in the furnace? Inefficient furnace operation? Increased carbon monoxide?

Thanks!

 

[steveray]

Good afternoon,

I came across a situation where the builder mixed up the intake and vent for the furnace, i.e., looking at the diagram in the Goodman manual, it was reversed. So, the intake was 12" above the vent instead of the opposite. I also noticed the water heater vent was way too close to the furnace intake compared with what's specified in the manual and also installed 12" below the furnace intake.

So, my question is, what are the hazards of the furnace intake bringing in combustion gasses along with clean air? They make concentric kits where the vent and intake are together but they're designed to separate the intake and vent.

I'm going to make note of it since the IRC says to follow the manufacturer's instructions but what is the actual hazard of the furnace intake bringing in combustion gasses? Dirty burning causing buildup in the furnace? Inefficient furnace operation? Increased carbon monoxide?

Thanks!

It'll be good to see some dialog on this, but instructions are instructions and have to be followed....

 

[TheCommish]

The manufacture has most likely had to test the air flow around the vent types as part of the listing.

 

[klarenbeek]

A couple problems I can think of off the top of my head.
1. Incomplete combustion. There's a much higher chance of flue gases being recirculated and used for combustion air.
2. Since the steam will go up, there's a good chance the intake will start icing over. if it gets to the point where the intake is too restricted, internal safeties will shut the furnace down. I've seen this happen. The space will be without heat until someone notices and fixed the issue. no heat over a long weekend or while on vacation can cause a lot of other problems in cold climates.
3. Done correctly, the intake elbows down and the exhaust blows out away from the building. With the exhaust blowing down out what should be the intake, you can and will get prolonged ice buildup on the side of the building. Flue gas condensate is very acidic so it will deteriorate the siding at a much quicker rate than normal water and ice. This is also why you can't turn the exhaust sideways to blow parallel with the building. I've seen this happen too.

Its actually an easy fix. Reroute the piping at the furnace to the opposite connection.

 

[ICE]

I also noticed the water heater vent was way too close to the furnace intake

Is the water heater also a direct vent appliance? With the advice from klarenbeek it seems that either way, the water heater vent shall be moved.

 

[bnymbill]

Thanks for the input - much appreciated, especially the details on potential issues.

The fix shouldn't be too bad as long as the builder still has/can get a piece of siding to match after moving the water heater vent. The water heater is direct vent.

 

[bnymbill]

I realized I forgot to ask, given that the intake was installed with the vent specifications, i.e., not with a downward elbow termination, what happens when rain/snow go in the intake? From 2" PVC, there's only so much that goes in but with a wind-driven rain in the right direction, you'd get a decent amount.

 

[Gregg Harris]

I realized I forgot to ask, given that the intake was installed with the vent specifications, i.e., not with a downward elbow termination, what happens when rain/snow go in the intake? From 2" PVC, there's only so much that goes in but with a wind-driven rain in the right direction, you'd get a decent amount.

It's not an issue. Rain that is driven in will drain through the secondary heat exchanger and out the drain.