The NORITZ NR98DVC is one of our best selling residential tankless water heaters for indoor applications. This heater is built around a Commercial Grade Copper heat exchanger that is 25% thicker than competitive models. Its direct vent technology is designed for indoor applications where an insufficient quantity of combustion air is available. This includes attics where closed cell foam has been applied, or closets where combustion air is limited. Utilizing concentric (double wall) venting, DVC series heaters pull their combustion air through the outer sleeve while pushing exhaust gases out the inner sleeve. What's more, by utilizing a quick connect cable, you can link two heaters together for increased capacity and redundancy. IK-WV-200-1-XX-LF valve kit (required for installation) is sold separately. NORITZ N-Vent concentric Venting is also sold separately. Controller and six foot power cord included.