The problems that arise after the transfer of ownership of HVAC systems usually revolve around the load was was calculated and sized, and not how the system was installed. Here’s five reasons why – and what steps you can take.
"The installation was clean. The charge was right. The ducting is tight. And the client still says the conference room doesn't cool."
If you run an HVAC contracting or design-build firm with a few crews across multiple sites, you've had this conversation — with your site engineer, with your service team, or with a client standing in a 30°C office under a brand-new cassette. Your team did everything right on site. Commissioning was done. And the complaint still came in.
The instinct is to look at the installation, because complaints arrive as field problems. But for firms running 10–20 people across several live projects, the root cause is usually upstream: in how the load was calculated — or not calculated — before a single duct was fabricated.
Here are five reasons why.
1. The sq ft/TR thumb rule is quietly costing you clients
Every estimator in India carries some version of a square-feet-per-TR rule in his head — one figure for offices, another for residential, another for showrooms. It works often enough to survive, and fails often enough to fill your service register.
Glass area and orientation, occupancy, lighting load, equipment heat, roof exposure, fresh-air requirement, ceiling height, ambient design temperature (a 45°C Jodhpur or Dubai summer is not a 34°C Bengaluru summer) — none of this is in a square-footage rule. When a thumb-rule estimate goes into a BoQ, you are gambling that the building is "average". The west-facing glass-fronted office is not average, and that's the one whose facility manager calls you in May.
2. No two people in your firm size the same way
Ask five people on your team how they arrive at a TR figure. One does a proper Carrier E-20 sheet. One uses the manufacturer's selector. One uses the thumb rule. One copies the consultant's BoQ without checking it against the as-built drawings. One asks the dealer.
This is not a people problem — it's a process problem. Without one standardised method that every estimator runs the same way on every enquiry, your quality is exactly as good as whoever happened to prepare that quotation. When you're not in the office, there is no guarantee the number on the proposal can be defended.
3. The consultant's figure (or the old unit's nameplate) is not your load calculation
On a retrofit, the existing nameplate is the fastest number available. On a new project, the consultant's tender BoQ is. Both feel authoritative. Neither is a load calculation for the building as it will actually be handed over.
The old unit may have been oversized from day one. The tender drawings may have had a different partition layout, fewer workstations, or no server room. Oversized systems short-cycle and leave humidity behind — the Mumbai and Chennai complaint. Undersized systems run flat out and never reach setpoint on a design day — the Rajasthan and Gulf complaint. Both generate the same phone call, and both look like installation failures when the client reports them.
4. You are the only person who sizes correctly — and that's the real bottleneck
Be honest: the reason sizing varies by estimator is that the correct method lives mostly in your head. You know how to read a floor plan, account for a west façade, adjust for a false ceiling with no insulation above it. But you can't attend every site survey, and you can't review every quotation before it goes out.
Owner-as-single-point-of-engineering-judgement does not scale. If accurate sizing needs your personal involvement and you have 12 active projects, something is going to be sized wrong — and it becomes a complaint during the first summer after handover that nobody can trace back to its origin.
5. There is no trail from quotation to complaint
When a comfort complaint comes in, can you pull up the original heat load for that room? Can you see who prepared the quotation, what inputs he used, what the calculated load was, and whether the BoQ actually matched it? If that lives in an Excel file on someone's laptop — or was never formally calculated — you can't learn from the complaint, you can't fix the process, and you can't defend yourself when the client withholds the retention amount.
Without a record connecting the engineering decision to the installed system, every complaint starts from zero.
What to do about it, starting now
- Pick one method and make it non-negotiable. Carrier E-20, ASHRAE, or a defined structured approach — one method, applied to every enquiry, by everyone.
- Build a sizing input checklist. Every quotation requires the same inputs: area, ceiling height, glass area and orientation, occupancy, lighting and equipment load, fresh air requirement, design ambient for the city. No inputs, no quotation.
- Put a review gate in place. Until an estimator is signed off on your method, a second set of eyes checks the load before the proposal leaves.
- Attach the load calculation to the quotation. If the engineering isn't connected to the price, it doesn't exist in any useful sense.
- Log complaints against project and team. If you can't see which projects generate service calls, you can't tell a sizing pattern from a crew pattern from an equipment pattern.
The conclusion worth reading
Complaint calls cost you margin, retention money, client trust, and eventually team morale. Fixing them starts with accepting that most comfort complaints aren't installation errors — they're engineering errors made weeks earlier, at the quotation stage.
If you want sizing to be standardised, documented, and attached to every proposal your firm sends out, that's what DuctArchitect is built for. It's HVAC ERP software for contractors: the heat load calculation flows into duct sizing and the BoQ, the BoQ becomes the quotation, the quotation becomes the project record, and every sizing decision stays retrievable when the client calls. No implementation consultants, no per-feature pricing — one connected workflow from enquiry to handover.