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Heating - Water Heater Large

I want an electric water heater.  Two of these are required in the house basement.  Typically large electric water heaters have two elements.  Buy the tall variant.  For power outage scenarios need to be able to operate just one element at 115V 20A.

AO Smith

Water Heater AOSmith 40Gal Tall 

https://www.lowesforpros.com/pd/A-O-Smith-Signature-50-Gallon-Tall-6-year-Limited-Warranty-4500-Watt-Double-Element-Electric-Water-Heater/1000216817   $439 + tax (About $400 + tax  when buy 2).

https://www.lowesforpros.com/pd/A-O-Smith-Signature-40-Gallon-6-year-Limited-Tall-Electric-Water-Heater/1000213649      $399    (About $360 when buy two).


Whirlpool 50-Gallon 240-Volt 6-Year Regular Electric Water Heater

Water Heater 50gal Whirlpool 

https://www.lowes.com/pd/Whirlpool-50-Gallon-240-Volt-6-Year-Regular-Electric-Water-Heater/1000000444    $389  (minus 5%, plus tax).    $350 each  (minus 5%, plus tax) if you buy two.

Dual 4,500-watt copper heating elements

49.75-in H x 23-in dia

Water Connection Size 3/4-in

Installation:  http://pdf.lowes.com/installationguides/035505161772_install.pdf 

Useful operational overview:  http://www.whirlpoolwaterheaters.com/learn-more/electric-water-heaters/how-electric-water-heaters-work/standard-electric-operation/

Electric Water Heater Installation


Two elements vs single element

With a two element water heater, the upper thermostat first sends electrical energy to the upper element until the water temperature in the upper third of the tank reaches the thermostat setting. Power is then transferred to the lower element until the remaining water reaches the lower thermostat setting.  If the water temperature exceeds 170°F, the high limit control switch will trip, shutting off power to the elements.

Single element water heaters have one element mounted at the bottom of the tank, controlled by a single thermostat and high limit switch.

Use two tanks

Using two tanks allows incremental buy, avoids someone using all the hot water, provides two heating elements, and provides redundancy from failure.  One serves one set of bathrooms and the other serves another set.  Provide shutoff valve mechanism for switching all bathrooms to one heater in case of failure.  Use one Geyser heat pump to feed both water heaters.

As all the hot water distribution to the house is PEX pipe in a star configuration, I divide into two zones so that someone using massive amounts of hot water in one bathroom (family bathroom) does not deprive another bathroom (my bathroom).  Connect the Geyser to tank one.  The hot water from tank one feeds zone 1 (family bathrooms) and also feeds into the 'cold' inlet on tank 2.   Zone 2 (my bathroom) is fed from the hot outlet on tank 2.  Geyser have approved this configuration.

Expansion tank

Connect the Thermal Expansion Tank to the cold water supply line near the water heater.  The expansion tank contains a bladder and an air charge.  To work properly, the Thermal Expansion Tank must be sized according to the water heater’s tank capacity and pressurized to match the home’s incoming water pressure.

Water expands when heated, and the increased volume of water must have a place to go, or thermal expansion will cause large increases in water pressure.  Most plumbing systems today are “closed,” and almost all homes now need a Thermal Expansion Tank.  A Thermal Expansion Tank is a practical and inexpensive way to help avoid damage to the water heater, washing machine, dishwasher, ice maker and even toilet valves.  If your toilet occasionally runs for no apparent reason (usually briefly at night), that may be due to thermal expansion increasing the water pressure temporarily.

Note that if your house is fed from a well then there is already a pressure tank and this can in practice handle any increase in cold water pressure caused by water expansion as water is heated.  I decided not to install an expansion tank, but it is possible that a building inspector may require one to be installed next to the hot water heater.

Having a good sized pressure expansion tank will help the sprinkler system work well (if you use 2" PVC pipe between the two systems).