Mechanical bids are built around equipment, and the equipment selections often differ: one bidder carries the basis of design, another a substitution with a different capacity or efficiency. Equipment substitutions belong in the comparison as clearly as the price.
The other big swing items are controls, test and balance, and insulation, which are often subcontracted and sometimes excluded entirely.
Typical scope items
What a complete mechanical and HVAC bid usually prices, and what to check in each:
| Scope item | What to check |
|---|---|
| Equipment | Rooftop units, split systems, terminal units, boilers or chillers. Note the manufacturer and model each bid carries. |
| Ductwork, diffusers and grilles | Supply, return and exhaust duct, with the air devices. |
| Piping | Hydronic, refrigerant and condensate piping. Gas piping may sit with mechanical or plumbing. |
| Duct and pipe insulation | Often by an insulation subcontractor. Confirm it is in the bid. |
| Building automation and controls | Carried by mechanical through a controls subcontractor, bid separately, or excluded. |
| Test and balance | Sometimes required to be an independent firm hired by the owner. Read the specification before treating it as a gap. |
| Startup, commissioning support and warranty | Startup by the manufacturer, participation in commissioning, and the warranty period. |
| Hoisting and rigging | Crane for rooftop equipment, and who sets the curbs. |
Common exclusions and qualifications
Not every exclusion is a problem. Some are fair because the work belongs elsewhere. The ones below are where mechanical and HVAC bids most often differ, so read them against the other bidders.
| Often excluded | Why it matters |
|---|---|
| Line voltage power wiring | Normally electrical. Make sure starters and disconnects are carried by someone. |
| Structural steel, supports and roof framing | Equipment support steel and framed openings are often excluded. |
| Roof curb flashing and roof penetrations | Mechanical sets the curb, roofing flashes it. Read both bids together. |
| Test and balance | Excluded by some bidders, included by others. |
| Controls | If excluded, carry a separate number before comparing totals. |
| Fire and smoke damper wiring | Often left between mechanical, electrical and fire alarm. |
| Cutting, patching and painting | A frequent gap between trades. |
Alternates to watch
- Equipment manufacturer substitutions
- Higher efficiency equipment or energy recovery units
- Extended compressor or parts warranty
- Added zoning or controls points
Line alternates up by the numbers on your bid form, keep add and deduct straight, and treat an unpriced alternate as a question, never as zero.
Unit prices and allowances to compare
- Added diffuser or grille, each
- Added controls point, each
- Ductwork, per pound or per linear foot
Compare rates only where the units match, and note any quantity already included in the base bid.
Where mechanical and HVAC meets other trades
Gaps and double counts happen at the edges. Read these packages together:
- Electrical (power wiring, starters, disconnects)
- Roofing (curbs and penetrations)
- Plumbing (gas piping, condensate)
- Structural (equipment supports and openings)
How Bidtab lays out mechanical and HVAC bids
Upload each bidder's PDF to one project for the package. Bidtab reads every bid and shows, side by side and in the order you uploaded them:
- each base bid, as stated;
- alternates aligned by number and description, with add or deduct for each bidder;
- a scope row for each item the bids address, with every bidder marked Included, Excluded, Qualified or Not stated;
- allowances and unit prices, with their units;
- each bidder's exclusions and qualifications as written;
- open questions where a bid is silent on an item other bidders addressed, where a figure isn't printed on the page it came from, or where line items don't add up to the total.
Every figure shows the page and words it came from, and the whole comparison exports to an Excel workbook. Bidtab doesn't rank bidders or price excluded scope; those calls stay with you. See the sample project (a roofing package) for the layout.