Should I replace the AC and furnace at the same time?

If both are near end of life, replacing together gives you one matched, right-sized system, one labor mobilization, and aligned warranties — often cheaper than two separate jobs. If only one has failed and the other is newer, a good installer confirms the AHRI match instead of upselling the pair.

Does replacing both as a system improve efficiency?

Yes, when it's done as a matched set. The rated SEER2 only holds for an AHRI-certified combination of condenser, coil, and air handler, and a whole-system changeout is the moment to right-size with an ACCA Manual J load calculation rather than copying the old equipment.

When should homeowners choose an AC and furnace combo replacement instead of separate jobs?

Consider a combined replacement when the furnace or air handler is near the end of life or mismatched with a new high-efficiency condenser. A combined job improves system compatibility, increases SEER2 performance, and simplifies permit and warranty paperwork. Request paired-equipment recommendations and coordinated load calculations from contractors.

Are city permits required for condenser replacement or full system swaps in Longmont?

Permits are typically required for condenser replacements and complete system replacements in Longmont. Permit requirements are managed locally rather than by the state. Always check with Longmont Building Division early to confirm whether a mechanical or electrical permit applies to the planned scope.

How do I get a quote from these AC replacement companies?

Submit one request on this page and we send it to the vetted AC replacement pros in Longmont, CO listed here. They send quotes back — no obligation.

Best AC & Furnace System Replacement in Longmont, CO

Last updated July 28, 2026

What to look for in AC & Furnace Replacement in Longmont

A whole-system changeout is the moment to right-size with a Manual J load calc and match the coil, condenser, and air handler so the rated efficiency is real. We weight installers who publish matched-system practice, manufacturer authorization, and Manual J sizing for the full job.

Whole-system / matched install. Provider names AC-plus-furnace or air-handler system replacement with the AHRI-matched combination — not two separate, unmatched halves.
Manufacturer authorization + labor warranty. Factory-authorized status and a multi-year labor warranty preserve coverage across the whole new system.
Manual J sizing. An ACCA Manual J load calculation right-sizes the system instead of copying the old (often oversized) equipment.

Verify before you book

Whether a Manual J load calculation was actually performed — ask to see the load-calc result.
That the coil, condenser, and air handler form an AHRI-certified combination — request the AHRI Reference Number.
License status with your state board — verify TDLR (TX), ROC (AZ), DBPR (FL), or your local equivalent before paying.

See full ranking methodology for AC & Furnace Replacement →

AC & Furnace Replacement in Longmont: matched system + sizing

A whole-system changeout is the moment to right-size with a Manual J load calc and match the coil, condenser, and air handler so the rated efficiency is real. Here is what each of the 2 installers below publishes: In Colorado, HVAC licensing is municipal (Denver requires a Class A or Class B mechanical license) — verify with your local building department before paying.

How we rank AC & Furnace Replacement providers → · Top picks meet at least one of: a category award, ≥2 verified signals, or Vouched Score ≥ 70.

Top picks

Welzig Heating, Air, Plumbing & Electric★ Best for Full-System Changeout
Consistently strong customer feedback (4.9★ from 1,445+ Google reviews).
Google 4.9★ (1,445+)
M and M Heating, Cooling, Plumbing and Electrical
Consistently strong customer feedback (4.9★ from 3,520+ Google reviews).
Google 4.9★ (3,520+)

Typical AC & Furnace Replacement costs in Longmont, CO (2026)

Last updated June 21, 2026

Estimated ranges for Longmont, CO. Actual cost varies with home size, equipment, and scope — always request a written quote for your job.

Service	Typical range
Full AC system replacement (3-ton, installed)	$5,700–$13,550
Furnace replacement (installed, paired changeout)	$3,100–$8,850
R-454B equipment upcharge (vs equivalent R-410A tier)	$415–$1,250

Why Longmont's seasonal swings make choosing an "AC Replacement" different

Longmont's hot summers and cold shoulder seasons drive variable load on home cooling systems, so timing and equipment sizing matter. Homeowners seeking best AC replacement companies in Longmont, Colorado should prioritize contractors who size systems for elevation and seasonal temperature swings.

Quick Picks

Best for Full-System ChangeoutWelzig Heating, Air, Plumbing & Electric

AC + furnace full-system changeout

Awards based on the same publicly available signals as the Vouched Score, including provider-stated certifications and dealer status. Not independently verified.

Which Longmont "AC Replacement" rules and timelines affect a home install?

Should I replace the AC and furnace at the same time?: If both are near end of life, replacing together gives you one matched, right-sized system, one labor mobilization, and aligned warranties — often cheaper than two separate jobs. If only one has failed and the other is newer, a good installer confirms the AHRI match instead of upselling the pair.
Does replacing both as a system improve efficiency?: Yes, when it's done as a matched set. The rated SEER2 only holds for an AHRI-certified combination of condenser, coil, and air handler, and a whole-system changeout is the moment to right-size with an ACCA Manual J load calculation rather than copying the old equipment.
When should homeowners choose an AC and furnace combo replacement instead of separate jobs?: Consider a combined replacement when the furnace or air handler is near the end of life or mismatched with a new high-efficiency condenser. A combined job improves system compatibility, increases SEER2 performance, and simplifies permit and warranty paperwork. Request paired-equipment recommendations and coordinated load calculations from contractors.
Are city permits required for condenser replacement or full system swaps in Longmont?: Permits are typically required for condenser replacements and complete system replacements in Longmont. Permit requirements are managed locally rather than by the state. Always check with Longmont Building Division early to confirm whether a mechanical or electrical permit applies to the planned scope.
How do I get a quote from these AC replacement companies?: Submit one request on this page and we send it to the vetted AC replacement pros in Longmont, CO listed here. They send quotes back — no obligation.