Why there is no average
The same nominal job — replace a three-ton split system — can differ by a factor of two between two houses on the same street. One has a reusable line set, a crawlspace you can stand in and a panel with spare capacity. The other needs new copper through a finished wall, a chimney liner because the water heater is orphaned, and a day of duct work because the return was always undersized.
Averages hide exactly the information you need. What helps is knowing the parts, so that when a bid is high you can find out which part is doing it.
The eight line items
| Line item | What it covers | The question |
|---|---|---|
| Equipment | Condenser, coil, furnace or air handler | Model numbers and the AHRI reference for the pair |
| Labour | Technician hours on site | How many hours, how many people |
| Line set | Copper, insulation, refrigerant | Reused or replaced, and flushed how |
| Sheet metal | Plenum, transitions, curb or pad | Fabricated on site or ordered |
| Duct modification | Returns, branches, sealing | Was static pressure measured first |
| Electrical | Disconnect, whip, breaker, service | Does a heat pump need panel work |
| Permit | Mechanical permit and inspection | Included, and who schedules it |
| Disposal | Recovery and removal of the old unit | Who documents the refrigerant recovery |
Why two honest bids differ
Overhead. A company with dispatchers, a warehouse, a warranty department and trucks that arrive when they said carries costs an owner-operator does not. Somewhere between 10% and 40% of a bid is overhead and margin, and that spread alone accounts for thousands on the same scope of work.
The other honest source of difference is scope. One bid includes a return upgrade and a proper commissioning visit; the other swaps the box. Both may be competent. Only one of them will fix the reason the upstairs was always warm.
A low bid is not automatically a good one
Missing lines to look for: no permit, no duct work in a house with high static pressure, a reused line set with no flush specified, and equipment that is not a matched pair. Each of those is money the bid did not spend and you will.
Two dates that move money
The Energy Efficient Home Improvement Credit (25C) could be claimed for improvements made through 2025-12-31: 30% of qualified expenses, capped at $2,000 a year for heat pumps and $1,200 for other qualifying property, $3,200 combined. A bid that still shows a federal credit line for work done now is wrong.
The second is 2028-12-18, when gas furnaces manufactured on or after that date must be at least 95% AFUE against 80% now. If your house vents into a masonry chimney, that step brings PVC venting and a condensate drain with it. Doing that work once, now, is cheaper than doing it twice.
Before you sign
- A load calculation, room by room, with the design temperatures stated.
- Model numbers for both halves and the AHRI certificate reference.
- A measured static pressure reading, taken before the duct was declared adequate.
- The permit named, with who pulls it and who meets the inspector.
- Labour warranty separate from the manufacturer's parts warranty, in writing.
Then build the price yourself in the replacement cost calculator and compare row by row. The gap is the conversation.
Sources: IRS, Energy Efficient Home Improvement Credit (read 2026-09-04) · 10 CFR 430.32(e)(1)(iii) (read 2026-09-04)