Manual J heat-load software
Size every room correctly in seconds. Vento runs a room-by-room heat load as you survey — accounting for glazing, orientation, insulation and occupancy — then selects the right unit and carries the result straight into the system design and the customer's proposal. No separate calculator, no re-keying.
Sizing that flows into the whole job
- Room-by-room cooling load, instantly
- UK / CIBSE design conditions you can set
- Glazing, orientation, insulation & occupancy
- Correct unit selection from a SEER/SCOP catalogue
- Multi-split system sizing across rooms
- Result carried into design and proposal automatically
Frequently asked questions
What is Manual J heat-load software?
Manual J is the room-by-room heat-load calculation used to size heating and cooling correctly — the US name for what UK installers do with CIBSE-style methods. Manual J software runs that calculation from the room's dimensions, glazing, orientation, insulation and internal gains, and gives you the capacity each room needs. Vento does this automatically as you survey, then carries the result into unit selection, system design and the proposal.
Is Manual J used in the UK?
The term is American, but the calculation is identical — UK installers size to the room's heat load using CIBSE design conditions. Vento uses UK design temperatures and lets you set your regional conditions, so the sizing is right for British homes rather than a US default.
How is this different from a rule of thumb?
A rule of thumb (e.g. 0.1–0.15 kW per m²) ignores solar gain, insulation and occupancy — two same-size rooms can need very different units. A proper room-by-room load accounts for each factor, so you don't under- or over-size. Try it free on our air-conditioning size calculator.
See also: air conditioning software, how to size air conditioning, and F-Gas software.
Size every room automatically
Manual J heat-load built into survey, design, proposal and payment — one platform for the whole air-con job. Free for 14 days, no card.
Start free trialMore of what Vento does
One platform — these are the parts of it installers ask about most.
- Air conditioning softwareThe whole job: survey, design, quote, e-sign and get paid.Read more
- Installer softwareBuilt for engineers on site, not adapted from a generic trade CRM.Read more
- Quoting & estimatingPriced from the survey, with your own materials and margins.Read more
- Proposals & e-signBranded documents with drawings, signed on the customer's phone.Read more
- F-Gas & logbookRegister, CO₂e totals and leak-check intervals, kept current.Read more