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the vent requires a 4 ft clearance

Where does that come from? Is it a Canadian thing?

I'm not saying that having an exhaust terminate near an attic vent is a good idea, but air is generally going out the attic vent, not in, and the attic isn't open to the living space. So I'm having a hard time imagining bad things happening.

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That's not something I would comment on.

you're right, in that case it is not that critical and it is not really worth mentioning.

The 4 ft clearance is from the manufacturer's installation guide. The vent should not be closer than 4 feet to any structure, wall, chimneys or anything that is higher.

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Most mfrs. of factory built fireplaces go with a separation laterally of 16-18" and a vertical separation of about the same for round terminations. Square terminations are of course at the same elevation.

When spaced too closely together, you run the risk of smoke/fumes/ heat from the lower exhaust being entrained into the concentric cooling space of the higher unit or being recirculated back into the home if under negative pressure. In the case where one chimney is for a heater, you always want the gas, oil or coal fired appliance's termination higher than any of the others due to the corrosive action of the exhaust as well as possible odors or CO. If the side of the taller chimney is showing signs of corrosion, call for replacing that section but also separate them wider with the heater exhaust higher than a fireplace or woodstove. In the case of a gas direct vent, discharging one heater too close to the termination may result in ghosting, delayed ignition, corrosion of the firebox, sooting, odors, or CO into the home.

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Reason I asked....

It doesn't look like that chimney extends up 3' above the roof penetration point. Is that required where you're at?

yes, a 3 ft minimum height is required and the chimney should be 2 ft higher than any structure in a 10 ft radius. In that case, I suspect the taller chimney was installed after which would explain the height difference and the roof vents are brand new.

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Reason I asked....

It doesn't look like that chimney extends up 3' above the roof penetration point. Is that required where you're at?

yes, a 3 ft minimum height is required and the chimney should be 2 ft higher than any structure in a 10 ft radius. In that case, I suspect the taller chimney was installed after which would explain the height difference and the roof vents are brand new.

Around here it's sort of common practice to stagger the heights of flues that are near each other, so I don't think the different heights necessarily indicates that they were installed at different times. And I don't think the 3-2-10 rule applies to other nearby flues.

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Around here it's sort of common practice to stagger the heights of flues that are near each other, so I don't think the different heights necessarily indicates that they were installed at different times. And I don't think the 3-2-10 rule applies to other nearby flues.

Thanks for the info. I'm no chimney specialist. WETT certification should be my next formation.

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