Rated heat output and rated heat input of combustion appliances

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A combustion appliance is an apparatus where fuel is burned to generate heat for space heating, water heating, cooking or other similar purpose.

According to Approved document J, Combustion appliances and fuel storage systems:

The rated heat input (or ‘rated input’) for a gas appliance is the maximum heat input rate at which it can be operated, as declared on the appliance data plate.

The heat input rate is the maximum rate of energy flow into an appliance, calculated as the rate of fuel flow to the appliance multiplied by either the fuel’s gross or net calorific value. Traditionally, the UK has used gross values, most European standards use net values. Thus for gas appliances it is now the norm to express this rating as a net value (kW (net))

The rated heat output for an oil appliance is the maximum declared energy output rate (kW) as declared on the appliance data plate.

The rated heat output for a solid fuel appliance is the manufacturer’s declared nominal energy output rate (kW) for the appliance. This may be different for different fuels.

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