tankless water heater venting

[Unregistered-Peter Misurek]

Hello-

I’m currently thinking about replacing a conventional tank type water heater with a new tankless water heater (Takagi T-K2). I understand this unit has a power vent whereas our old water heater did not. Our current water heater vents into a chimney flue right next to it (3″ vent). We had an old furnance at one time that looks like it vented into a different flue via a much larger hole that is capped off. My question is, would it be ok to vent the tankless water heater out this flue with some sort of adapter to step it down to the 4″ required vent pipe? Can you vent power vented appliances out a chimney flue or do they need to vent directly to the outside?

Thanks,

-Peter

[Unregistered-Paul]

My research thus far on the subject (I’m looking at Takagi myself) is that they generally need to be vented through the chimney via Category 3 4″ ducts (code in NYC) unless you are purchasing a direct vent model. Takagi has both direct vent and non-direct vent models. However, with a direct vent model, it is my understanding that they tend to create a lot of steam in the colder months (think of it as seeing your breath in the cold). If the vent is at a low level, you’ll wind up with clouds of “steam” at eye level rather than having any such “steam” escaping at the roof line. Takagi has a good tech line, look them up on their site, and, BTW, I’d look at getting the newer model, the TK-1S vs. the T-K2. It is lighter, and it’s GPM is a bit higher than the TK-2.

Good luck.

[Anonymous]

A gravity tank water heater is about 35,000 BTU’s and a tankless can be 150,000. The vent system must handle much hotter gases and you should use the venting specified for that unit.

[Author]

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