Sketch, component list, proposed operation

electric hydronic system for 760 sq ft garage house addition

The above sketch (to scale, one square = 2") is a plan for installing a HydroShark3-10 electric boiler to heat a 769 sq ft attached garage.

Following are details about this plan:

Garage/House Addition - consists of a 21 x 21 garage, 14 x 6 entrance boot room, (2) 9 x 11 offices, and a 4 x 6 mechanical room. Built in 1999, 4" slab on grade beam, R20 walls, R40 ceilings, 2"  rigid SM styrofoam under and around slab, triple glaze vinyl windows, 2" insulated steel Wayne Dalton garage door and insulated steel ext doors. Northern Canadian climate, typically get 6 weeks of -30 to -40 C every winter. We get snow from Oct to April, sometimes from Sept to May.

Previous heating system - 33 gallon NG DWH connected to (4) x 100' long loops of 1/2" Kitec (it looks fine despite the class action lawsuit against it).  The old set up was a primitive open system which kept the building warm but the unit rusted out this spring. Now I have decided to switch to electric and upgrade to a proper pressurized clean closed system with 30% PG/water. I pressure tested the loops with air (via the previous piping system) last week at 40 PSI and it only dropped to 38.5 PSI over 12 hours so I know the loops are operable.

New component list:
Boiler: HydroShark3-10
Primary Pump - Grundfos UPS15-42
Secondary Pump - Taco HEC-2 Bumblebee
Flowmeter - Dwyer VFC141EC  0.5 to 5 GPM rotameter
Purge and Fill Valve - Webstone 58613
Air Separator - Taco 4900
Safety Relief Valve - Watts 30 PSI Series 335
 P/S Purge Tee - Webstone 58643
Y Strainers - 3/4" Asahi PVC
Expansion Tank - 2 GAL Amtrol or equiv
Temperature/Pressure Gauges - Watts LFDPTG-1-3 0-75 PSI 60-320 deg F
Isolation valves - Webstone 51703T
kWH meter - Itron Centron .5-200A 240V 1ph Type C1S  3 wire (Sangamo GCA0001)
P/S system piping - 3/4" L Cu soldered except the system feeder line which will be 1/2 L Cu.
System Feeder - Axiom MF200

Proposed operation:
Primary pump will be controlled by a dumb Honeywell 120V line voltage thermostat. When it calls for heat the primary will pump 2 GPM through the HydroShark which will be set at 120 deg F.
The secondary pump will be controlled by the delta T sensors, initially 20 deg F delta T.
System pressure = 15 PSI. The kWH meter will allow me to monitor the cost of heating the space at the current rate of $0.12 per kWH.

Future consideration - enough space was left on the wall so that a larger electric heater can fit if the HS3 is too small.

mechanical room stripped ready for install

Comments are welcome, thank you for any input.