Why your HVAC quotes don't match (and how to compare them)

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In real Northern Virginia quotes we’ve reviewed, two quotes for the same kind of system (a central air conditioner with an 80% gas furnace) were about $9,000 apart. One bundled a UV light, a premium filter and an added return duct; the other didn’t. Neither was wrong. They just weren’t the same job. See what replacement costs locally for the full set.

The seven places quotes differ

1. System size

Size is measured in tons for cooling (one ton is 12,000 BTU per hour) and BTU for heating. One contractor may match your old unit, another may go bigger “to be safe”, and a third may calculate it. An oversized air conditioner cools quickly, shuts off before it removes humidity, and leaves rooms clammy. The size should come from a room-by-room Manual J load calculation.

2. Efficiency and stages

A single-stage system runs at full blast or not at all. Two-stage and variable-speed equipment run longer at lower output, which is quieter and more even, and costs more. Efficiency changed from SEER to SEER2 ratings in 2023 (what SEER2 means); SEER2 reads a little lower for the same unit, so a “16 SEER” and a “15.2 SEER2” quote may be describing similar equipment. Make sure you compare the same rating.

3. Matched equipment and model numbers

The outdoor unit, the indoor coil or air handler, and the furnace should be a certified matched set. A quote that says “16 SEER system” without model numbers can’t be checked. With model numbers you can look up the rated efficiency and the warranty yourself.

4. Refrigerant lines

The copper lines between the indoor and outdoor units can sometimes be reused and flushed, and sometimes must be replaced, depending on their size, condition and the refrigerant the new system uses. The industry is moving from R-410A to newer refrigerants such as R-454B and R-32. Replacing a line set run through finished ceilings is real work, and it is one of the most common gaps between a low quote and a high one.

5. Ductwork, especially returns

Undersized return ducts (the side that pulls air back to the system) are a common problem in existing homes. A new system can’t move air the ducts won’t carry. One quote may add or enlarge a return; another may connect to what is there.

6. Electrical, gas, venting and drainage

A new disconnect, a breaker or wire change, gas piping and bonding, flue and venting updates, a condensate pump or drain route: each one can be included, excluded or left vague. So can the permit and inspection.

7. Warranty, add-ons and discounts

Parts warranties usually require registering the equipment. Labor warranties range from 1 to 10 years. Add-ons like UV lights, media filters, surge protectors and smart thermostats are often bundled in. And quotes may show large discounts already applied. Compare the final price for the defined scope, not the discount.

How to make quotes comparable

1. Measure first. Get a Manual J load calculation so the size is settled before anyone quotes.
2. Write one scope. List the equipment type and size, and the work around it: line set, returns, electrical, gas, venting, drainage, permit.
3. Ask every contractor to price that scope. Alternatives are fine, but ask for them as separate line items.
4. Line the quotes up side by side. Same rows for every bid: model numbers, size, efficiency, included work, warranty, start date, payment terms, price.

Here’s what that looks like in practice: a sample comparison of three bids on the same scope, with the gaps flagged.

Questions to ask every contractor

• What size is this system, and how did you calculate it?
• What are the exact model numbers, and is it a certified matched set?
• Are you replacing or reusing the refrigerant lines? Which refrigerant does the new system use?
• What duct changes are included? Is the return large enough for this system?
• What electrical, gas, venting and drain work is included?
• Is the permit and inspection included?
• What are the parts and labor warranties, in years? Who registers the equipment?
• Which items are optional add-ons, and what does each cost on its own?

Or let someone do it for you

1Stop is an independent service for homeowners in Loudoun, Fairfax and Prince William counties. We don’t install systems or work for any contractor. A Comfort Consultant measures your home, writes one scope, and vetted local contractors bid on exactly that job, so you can compare them line by line. It’s free for homeowners.