Short answer: before comparing totals, check whether both quotations assume the same scope boundary, the same programme duration, the same labour-only-versus-supply-and-install basis, and whether one has simply excluded more than the other. Line them up on those four points first, and the price gap often either shrinks to nothing or turns out to be the only honest number in the room.
A quantity surveyor comparing two ductwork quotes is doing something harder than it looks, because "ductwork installation" isn't a single defined product. One subcontractor might price against the drawings as issued, assuming standard access. Another might have visited site, spotted that the riser is only accessible from one end, and priced a longer duration and a smaller crew to match. The second number is higher — and probably the more honest one.
The normalisation method
Start with scope boundary, not price. Read both quotations for where the package starts and stops. If one quotation's boundary is tighter, its lower price isn't a saving; it's a smaller job.
Check the exclusions list against each other. A quotation that excludes builder's work, fire-stopping, or scaffold hire looks cheaper right up until those costs turn up separately later.
Confirm labour-only versus supply-and-install. These aren't variations on the same price — they're different products.
Compare the programme duration each price assumes. A shorter quoted duration sometimes means a leaner method. It sometimes means the subcontractor hasn't yet accounted for a shared ceiling void or a single-point delivery constraint that will surface as a variation once they're on site.
Look for provisional sums, and check they're marked as such. A quotation with an unresolved design element folded into a firm price may have just declined to flag the risk.
A quick illustration
Say two subcontractors quote for the same fit-out package, four thousand pounds apart. On paper, the higher quote looks like the worse deal. Read the small print and the lower quote excludes fire-stopping at duct penetrations and assumes a five-week programme with no allowance for shared access with electrical first-fix; the higher quote includes fire-stopping and assumes six weeks, matching the actual sequencing on the job. Normalise both, and the "expensive" quote is the cheaper one once the excluded work gets priced separately and the shorter programme inevitably slips.
Common mistakes
Ranking quotations by total price before checking the scope boundary. Missing an exclusions list buried in small print. Comparing a labour-only price directly against a supply-and-install price without adjusting for the difference. Accepting an unusually short programme duration at face value.
What Cliventa provides
To give you a quotation that's genuinely comparable, Cliventa needs the same drawings, specification and programme information you sent to any other subcontractor being quoted against. We structure our return quotation with scope, exclusions and programme assumptions stated clearly, so it can be normalised against whatever else is on your comparison sheet.
Not sure what to send in the first place? Start with our note on what a ductwork contractor needs to quote, or see our ventilation installation page for service fit.