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Originally posted by alinnova
The Mendota cap and those specified by other brands that also use short pipes for combustion air have vent caps at the top that breath.

A point of correction in what I said here. Mendota instructions call for using a Dura-Vent or an Ameri-Vent cap.

Al

Collin, I see your point, thanks. The Mendota instructions requires that the damper opening be sealed around the vent pipes to prevent using room air for combustion. The Mendota cap and those specified by other brands that also use short pipes for combustion air have vent caps at the top that breath.

But if the seal at the damper is less than perfect, or if it deteriorates over time, then some warm room air would go up the exhaust. This is why I would prefer the coaxial system.

Al

Seems kinda strange. If the cap is well sealed at the top, it seems to me you would be pulling combustion air from the room.
Every direct vent insert we install has both liners going all the way to the termination.
Having said that, always stick to the manufacturers installations.

Can one use a 6 inch coaxial vent system with the Mendota D-40 gas fireplace insert that is placed in a masonry fireplace?

The web site .pdf copy of the installation manual shows that for a masonry fireplace, they use a 4 inch colinear direct vent system where the combustion air intake rises about four or five feet above the appliance. For a zero clearance fireplace, they use a coaxial vent system.

I believe I should prefer a system that takes combustion air directily from the vent cap at the top of the chimney.

Thank you, Al