Rated heat output and rated heat input of combustion appliances
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.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
We're expanding our collaborative mission by launching DB Intelligence, an exclusive market research advisory panel. Built environment professionals can now get paid to share their expertise on industry trends, products and services.
Panel members receive direct financial incentives for participating in research projects like short surveys, 1-2-1 interviews and focus groups. Register today to shape the future of the construction sector.
Building Control Independent Panel final report
A precis of a key report led by Dame Hackitt with full recommendations and link to the government response.
Guide to ISO 19650 for Architecture Firms (2026)
A user gives their low down.
A UK training and membership provider for mould remediation professionals.
Building Safety recap April, 2026
A short and longer run-through of the month, with links to further information and sources.
CIAT May 2026 briefing.
Independent NSI and BAFE study exploring how organisations are changing the way they buy fire safety services.
From medieval scribes to modern word art.
ECA welcomes crackdown on late payment and push for clean energy, whilst CIOB seek fixed cladding removal timeframes.
Cyber Security in the Built Environment
Protecting projects, data, and digital assets: A CIOB Academy TIS.
Managing competence in the built environment
ITFG publishes new industry guide on how to meet the ICC principles.
The UK's campaign to reduce noise pollution: Mythbusting, articles and topic guides.