Questions -
To maximise efficiency, boiler selection should be based on an in-depth survey of the property and an estimated calculation of heat loss inside the dwelling. Once the energy (kW or BTU/hr) requirement for the property has been assessed the boiler should be matched against this energy rating.
Rinnai UK recommend all appliances are serviced annually.
No. All Rinnai Water Heaters will protect themselves down as low as -15°C providing the electrical supply is left ON. They will NOT however protect any external pipe work against frost damage.