Furnace and AC Replacement in Denver

When replacing both actually makes sense

There are three situations where doing the furnace and air conditioner together is the right call, and one where it isn't.

Both are near end of life. Gas furnaces run 15 to 20 years; central air conditioners are similar, often a little less in a climate with hot dry summers. If they were installed together — which they were, in most Denver homes — they age together. Replacing one and returning for the other in eighteen months means paying twice for the same access work.

The furnace died and the AC is 12+ years old. This is the most common version. You're already committed to an installation, the technician is already in the mechanical space, and the incremental cost of the second system is lower than it would be standalone.

You're changing efficiency tiers or fuel. If you're converting the furnace to a 95% AFUE condensing unit, or weighing a heat pump, the whole system's design changes. Doing it piecemeal risks a mismatch you'll pay to correct later.

When it doesn't make sense: your AC is under about eight years old and working. There's no efficiency argument strong enough to justify tearing out equipment with a decade of life in it. A contractor who pushes a full system replacement in that situation is selling, not advising.

What you actually save doing it together

The savings are real but they're in labor, not equipment. The equipment costs what it costs.

What you avoid paying twice for: mobilization and access, the sheet metal and plenum work where the coil meets the furnace, the condensate drain, electrical connections, permit coordination, and the second day of two technicians' time.

What you don't save on: the furnace itself, the condenser, the coil, the refrigerant line set if it needs replacing, or the permit if your jurisdiction requires separate mechanical permits.

A furnace alone runs $6,300 to $8,650 installed in Denver. Combined replacement lands in the low-to-mid five figures depending on capacity, efficiency tier, and how much of the existing infrastructure is reusable.

Ask for it quoted both ways — as one project, and as two separate projects a year apart. The gap is the actual saving, and it lets you decide with a number instead of a claim.

The matched-system argument, honestly

You will hear that furnace, coil, and condenser must be a matched set. The claim is legitimate and it gets oversold, so here's where the line is.

True: a high-efficiency condenser paired with an old, undersized evaporator coil will not deliver its rated SEER. The system performs to its weakest component. If you're buying an efficient AC, the coil has to suit it.

Also true: the coil sits directly above the furnace in most Denver installations, so replacing a furnace often means disturbing the coil anyway.

Oversold: the idea that working equipment must be replaced because it wasn't sold as a bundle. Plenty of well-performing systems are mixed. A properly sized coil paired with a good condenser works whether or not the badges match.

The honest test is whether the existing component is near end of life or genuinely mismatched — not whether a catalog groups them.

The heat pump question

If you're replacing both machines anyway, this is the moment to at least price the alternative.

A heat pump does both jobs from one outdoor unit — it cools in summer and reverses to heat in winter. And Colorado's incentive structure makes the comparison unusual: Xcel pays $2,250 per heating ton for a cold-climate heat pump with the bonus, roughly $6,750 on a typical 3-ton system, against $225 for a gas furnace.

That bonus drops on October 1, 2026, and there are eligibility conditions. Heat pump vs furnace in Denver works through the cold-weather performance question, the electrical panel cost that can erase the advantage, and when a gas furnace is still the better buy.

Many Denver homes end up on dual fuel — keep the gas furnace, add the heat pump, let the system switch at the crossover temperature. If you're replacing both anyway, that's worth a quote.

Sizing both for a Denver house

The altitude derate applies to the heating side: gas furnaces lose roughly 4% of rated capacity per 1,000 feet, and the metro sits above 5,200 feet. Cooling capacity is affected differently — thinner air carries less heat, which changes the load calculation rather than simply derating the equipment.

The practical point is that both systems need real calculation rather than matching the old nameplates, and one contractor doing both at once has a better view of the whole picture than two contractors doing halves.

Ductwork is the shared constraint. Both systems push air through the same ducts, so if the returns are undersized — common in Denver, where the median home dates to 1975 — neither system reaches its rated performance. If you're replacing everything else, it's the right time to find out. Duct modification runs $1,600 to $5,550 and up.

Get it priced both ways

Ask for three numbers: furnace alone, AC alone, and both together. Then you can see the actual saving instead of taking someone's word for it.

Call (303) 226-1486 or send the form. One insured local heating professional will quote it honestly, including telling you if your AC has years left and you only need the furnace.

More detail: furnace installation cost in Denver, high-efficiency furnaces, and Xcel's rebates.