Factors to consider when selecting a storage (tank) type hot water heater
Warranty - manufacturer’s specific warranties may vary greatly by series and model and commonly include separate warranty for tank and parts. Most common warranties are 6 and 10 years with a few in between (i.e. 8 yrs) and some above (10+ yrs).
Capacity - tank storage volume will directly impact the 1st hour rating (how much hot water can be delivered within the first hour after all the water in the tank is fully heated and ready to use) and therefore determines whether the specific size will work for your household size.
Dimensions - headroom may be an issue in some installations, so check the dimensions and make sure there’s sufficient space to install and pipe the heater (especially for gas WH’s, which require flue vent piping). If installing the water heater in a closet, make sure it fits into the door frame.
Energy efficiency - is among the most important factors, since it will determine how efficiently the unit will operate and will help to compare different models to make a balanced choice between initial investment and long-term energy savings. Also consider that in some areas of the country, homeowners may quality for a rebate when installing "Energy Star" appliances.
Additional features - such as factory-installed heat traps, self-powered gas valves (on gas models), recirculation outlets (for hot water recirculation), sacrificial anodes, sediment self-cleaning, etc.