Carbon Monoxide Danger

[Geoffrey Smith]

3040730408

Just wanted to get some clarification on this as 2 previous HVAC techs looked this natural gas boiler over and one previous home inspector.
The boiler has one single wall pipe venting into the chimney but the other side was left completely open.
I wrote it up as a safety hazard due to possible Carbon Monoxide gas leaking into the house. Comments please.

[Lon Henderson]

Agree. But did you check for CO spillage?

[Geoffrey Smith]

No. I didn't. This was at my sister's house in Buffalo NY. I was visiting over the Easter break from Albany and didn't bring my tools - just a free inspection of a new house she bought.

[Mark Reinmiller]

3040730408

Just wanted to get some clarification on this as 2 previous HVAC techs looked this natural gas boiler over and one previous home inspector.
The boiler has one single wall pipe venting into the chimney but the other side was left completely open.
I wrote it up as a safety hazard due to possible Carbon Monoxide gas leaking into the house. Comments please.

It is wrong, regardless of whether there is any spillage at the time you are there. That looks like an old draft hood that would be used when the flue comes out of a boiler or furnace horizontally. Then the open part faces down, which would be correct. Also, boiler manufacturers typically specify a minimum vertical distance that a draft hood should be above a boiler. I'd bet that the draft hood is too close to the boiler.

[Ed Gerhardt]

It is wrong, regardless of whether there is any spillage at the time you are there. That looks like an old draft hood that would be used when the flue comes out of a boiler or furnace horizontally. Then the open part faces down, which would be correct. Also, boiler manufacturers typically specify a minimum vertical distance that a draft hood should be above a boiler. I'd bet that the draft hood is too close to the boiler.

I've been out of the game for a while now, but I would expect to see a barometric damper at that location.

[Jimmy Roberts]

3040730408

Just wanted to get some clarification on this as 2 previous HVAC techs looked this natural gas boiler over and one previous home inspector.
The boiler has one single wall pipe venting into the chimney but the other side was left completely open.
I wrote it up as a safety hazard due to possible Carbon Monoxide gas leaking into the house. Comments please.

While this hood appears to be a leaker, and it may well be at times, air pressure dynamics likely will keep exhaust gasses going up the chimney. This open hood will continually allow warm air to travel up the chimney, toward the cold outside air. This creates slightly negative pressure at the open end. Because warm air is continually traveling toward the chimney, when the boiler is burning, the warm gas/air from the burner will naturally follow the negative pressure that is already traveling toward the chimney. Just like with a hood which is vented below the flu entry point, it is unlikely for exhaust gas to escape into the room, except by blocking the chimney.

[Lon Henderson]

While this hood appears to be a leaker, and it may well be at times, air pressure dynamics likely will keep exhaust gasses going up the chimney. This open hood will continually allow warm air to travel up the chimney, toward the cold outside air. This creates slightly negative pressure at the open end. Because warm air is continually traveling toward the chimney, when the boiler is burning, the warm gas/air from the burner will naturally follow the negative pressure that is already traveling toward the chimney. Just like with a hood which is vented below the flu entry point, it is unlikely for exhaust gas to escape into the room, except by blocking the chimney.

On a nice calm day or not too cold, you're probably correct. But windy days can push combustion gasses into the room. Very cold days can cause a thermal cap to form in the flue and cause spillage, maybe significant spillage. Just bringing combustion air into the boiler room, might cause spillage.

[John Kogel]

The installation manual will show what the correct draft hood should look like. Nothing like that, I'll bet.

Google the make, model # followed by 'manual'.