Direct Vent Models?

Tremolux

We're restoring an old house and want to go with a direct-vent gas hot water system with air input & exhaust piped through a basement window. Since it's a three unit building, ( 2 small 2nd floor units ) it needs a larger than usual model ( 40 - 50 gallons ) but it won't actually be needing that much most of the time. There won't be tenants, and the new Pex lines allow us to shut off the upstairs hot water when unused.



Are there any major differences between major brands?



( Unpowered vents are preferred. )



Any differences in installation?



Any with better warranties?



Thanks for your help.

Ironman

Tankless

Why don't you go with a tankless? From what you're describing, It would be ideal for your situation.

Tremolux

Too much upkeep ... etc.

The problem with tankless is the mineral content of our water.



The water quality is good, but the mineral content requires acid cleaning tankless heaters on a yearly basis. No thanks.



They are well suited to 3rd floor applications, but this is only 2, and all the lines are already Pex.



We're actually thinking of two separate heaters ... one for each floor.



There won't be any dishwashers or laundry up there, just two small kitchens & baths.



When not used, they can be on "vacation" during the Winter to keep from freezing, or turned off entirely in the Summer.

EricAune

Minerals or non-conditioned water supply?

Any heater is going to be adversely affected by high mineral content; water conditioning is the first step in prolonging the life a all water heaters. 



All tankless units require annual flushing, that being said I would consider even half the expected life-span (6-8 instead of the expected 10-15 years) of a quality tankless to achieve savings over a direct vent tank model with the same water quality.  Those direct vent models are pricey without any major advantage in operating savings.  Consider the cost of possible tank failure from corrosion due to the water quality.