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Tank -> Demand Heater Installation

558 Views 2 Replies 3 Participants Last post by  Ghostmaker
Hi there,

I'm planning on replacing my 75 gallon NG tank with a demand heater installation. I've ordered a Takagi T-H3-DV-N. I have a couple of questions:

1) Is there anything that would prevent me from re-using the exhaust of the existing water heater? The Takagi installation manual shows various rooftop vent installation options; I would like to take advantage of the existing rooftop vent, if possible.

2) I recently had a new furnace installed with has dedicated inlet outlet vents. I plan on having the direct vents installed on this demand heater as well (to take advantage of added efficient of using outside air for the input. I've noticed I have this fresh air vent that just passes in outside air into the general furnace/hot water tank is just spilling in cold air. I believe I have rendered this vent obsolete by installing this demand that true?


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dont use the vent through the roof with the existing flue pipe, the old heater was natural draft, the new takagi is induced draft and uses special vent pipe, if you pipe in fresh air into the takagi from outside you can close up tho old fesh air into the the new furnace you put in also has fresh air piped into it..
Venting with Schedule 40 PVC, CPVC, PP, Category III stainless steel

Listed under the specs.

You may need to resize your gas line Maximum BTUs: 199,000

This is a direct vent unit. Out through the side of the house in scd 40 solid core PVC pipe.. NO FOAM CORE ALLOWED NO ABS ALLOWED.

Product manual:
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