Compare identical outcomes, not different-looking totals
One quote can include a premium model, dedicated electrical work, a condensate pump, access tower, full commissioning and seven-year warranty support. Another can show only “supply and fit air conditioning.” Those totals are not competing prices for the same job.
Start with the exact indoor and outdoor model numbers and the rooms each system serves. Ask what heat loads were calculated and whether simultaneous demand was considered for a multi-split. The quote should show pipe routes, included length, trunking, outdoor-unit position, condensate disposal and whether pumps are required.
Scope that commonly reappears as an extra
Electrical circuits, fused spurs, isolators, consumer-unit work, scaffold or towers, roof protection, core drilling, decorating, planning applications and freeholder submissions can all sit outside a headline price. VAT must be clear. If an exclusion is likely, obtain a budget or separate contractor quote before comparing totals.
Commissioning is part of installation, not an optional flourish. The contractor should pressure-test, evacuate, charge or verify charge as required, test drainage, confirm operation, record commissioning data and hand over controls and maintenance instructions. The company carrying out refrigerant work must hold the appropriate F-Gas certification.
Red flags that deserve a pause
Pause where the proposal has no model numbers, describes capacity only as “suitable,” requests a large cash deposit without clear terms, or promises that planning and the freeholder “will be fine” without checking. A verbal promise to hide pipework, make good decoration or include scaffold is not part of the contract until it appears in writing.
Be equally cautious with artificial urgency: expiring today-only discounts, pressure to finance before seeing the cash scope, or a claim that the largest unit is safest. Good installers may have busy diaries and time-limited supplier pricing, but they can still document the design and let you read it.