Three summers in a row have made this the most common call we get from the valley: the furnace is fine, the house is not, and the upstairs hits 84 degrees by four in the afternoon. Kent, Auburn and Renton are full of 1970s through 1990s homes that were built with heat in mind and cooling as an afterthought. Adding air conditioning to them is a well-worn job — and the pricing is far less mysterious than most quotes make it look.
Here are the real 2026 numbers, what moves them, and the one comparison that saves a lot of people money.
The short answer: $5,000 to $12,000
Adding central air conditioning to an existing furnace and ductwork runs $5,000 to $12,000 installed in Kent, Auburn and Renton. All three cities sit in the standard market tier, so none of them carries a premium — a 2,000 square foot split-level on Kent's East Hill and a similar house in Auburn's Lea Hill quote out of the same range.
| What you're buying | Installed cost |
|---|---|
| What you're buyingAdd central AC to an existing furnace | Installed cost$5,000 – $12,000 |
| What you're buyingReplace furnace and AC together | Installed cost$10,000 – $16,000 |
| What you're buyingDucted heat pump (heats and cools) | Installed cost$12,000 – $18,000 |
| What you're buyingDuctwork repair or replacement, if needed | Installed cost$3,000 – $8,000 |
Where you land inside that range is not random. It comes down to four things.
The four things that actually move your price
1. Cooling load, not square footage
Most homes in these three cities need somewhere between 2 and 4 tons. A bigger system costs more, obviously — but the trap is the opposite direction. Oversized air conditioners cool the thermostat's hallway fast, shut off, and leave the rest of the house clammy. They short-cycle, which wears the compressor out early.
A real Manual J load calculation weighs insulation, window area and orientation, ceiling height and layout. Every one of our estimates includes it at no extra cost, because guessing by square footage is how homeowners end up paying more for worse comfort.
2. Ductwork condition
This is the big variable in the valley. Cooling is less forgiving than heating — cold air is denser, leaks hurt more, and a duct system that limps through winter will not deliver a comfortable summer. Crawl space ducts in Kent and Auburn have been sitting in damp conditions for decades. Collapsed flex, disconnected boots and saturated insulation are common finds.
If the ducts are sound, nothing changes. If they need work, add $3,000 to $8,000 depending on scope. We tell you which one it is before you sign anything, with photos.
3. Electrical capacity
An outdoor condenser needs a dedicated 240V circuit and a disconnect. Most homes here have a 100-amp panel or larger and handle it without drama. Older Renton and Kent homes still running a crowded panel or a 60-amp fuse box may need an electrician involved, which is a separate line item coordinated with your install.
4. Equipment tier
We quote Good, Better and Best on every job. A single-stage condenser at the efficiency minimum is the lowest number on the page. Two-stage and variable-speed equipment costs more up front, runs quieter, and removes noticeably more humidity because it runs longer at lower speed. In a two-story home with a hot upstairs, that difference is worth paying for more often than not.
What's different about each city
Kent
East Hill and West Hill are dominated by split-levels and ramblers with existing ductwork — the easy lane for an AC add-on. The complication is the split-level itself: one thermostat on the middle floor controlling three half-levels. Correct sizing and return air capacity matter more here than equipment brand.
Auburn
Valley floor and Lea Hill. Auburn has the mildest winter design temperature in our entire service area at 25°F, which matters less for cooling than for the heat pump conversation below. Plenty of 1980s and 1990s subdivisions with usable ducts, plus manufactured homes where a ducted condenser is not practical and a ductless system is the better answer.
Renton
The Highlands, Benson Hill and the valley all price the same, but Renton is one of the few cities in our area that is split between two electric utilities — some addresses are billed by Seattle City Light, others by a different local utility entirely. That makes no difference to an AC price, but it makes a real difference to rebate eligibility if you end up going the heat pump route. We read it off your bill rather than guessing from your zip code.
The comparison most quotes skip
Here is the honest part. If your furnace is young and healthy, standalone AC is the cheaper, simpler move and we will install it without trying to talk you into something bigger.
If your furnace is 15 or more years old, do the math differently. Adding AC now at $5,000 to $12,000, then replacing a dead furnace in three years, means two installs, two permits, two disruptions. A ducted heat pump at $12,000 to $18,000 replaces the air conditioner and the heating system in one piece of equipment, uses the same ducts, and cools exactly the way an AC does — it is the same refrigeration cycle, just able to run in reverse.
There is a second reason to weigh it. Local utility rebate programs in Washington are aimed at heat pumps, not cooling-only equipment. Cooling-only installs generally don't qualify. Our Washington rebate guide walks through how that works, and the short version is that rebates follow the meter, not the county. The amount depends on the utility billing your home, what is being replaced and the efficiency installed. Programs change, so we confirm what your utility actually pays before quoting it and file the paperwork as part of the job.
One more thing to be clear about: the federal 25C tax credit ended December 31, 2025. No 2026 installation qualifies, regardless of what anyone's flyer says.
What a real quote should contain
If the number on your estimate is a single figure with no breakdown, ask for more. A straight proposal shows:
- The tonnage and the load calculation it came from
- Make, model and efficiency rating of the condenser and coil
- Whether the existing furnace blower is compatible
- Duct findings — in writing, with what is and isn't included
- Electrical scope and who performs it
- Permit and inspection, which is required in all three cities
- Warranty terms, parts and labor, with years
We pull the mechanical permit on every job. Skipping it is a problem at resale, because Washington's seller disclosure form asks directly whether unpermitted work was done.
Want a ballpark before anyone comes out? The instant estimate tool gives you Good, Better and Best starting prices in about 60 seconds from seven questions about your home.
Install day
Most add-on air conditioning installs in Kent, Auburn and Renton are done in one day. The crew protects floors, sets the condenser on a pad in the side yard, installs the evaporator coil on the furnace, runs the line set and condensate drain, pulls the electrical circuit, evacuates and charges the system, then commissions and tests it. Duct work or a difficult condenser placement can push it to two days, and you hear that at the estimate, not on the morning of.
Placement is worth five minutes of thought. Modern condensers run quiet, but not silent — away from bedroom windows and off a shared property line is always the right call.
Get a real number for your house
AC pricing in these three cities is not a mystery. It is a load calculation, a duct inspection, an electrical check and an equipment choice. Everything else is packaging.
See the full scope of what we do on the AC services page, then book a free in-home estimate or call (253) 785-4622, Monday through Friday, 8 to 6. We will tell you honestly whether AC alone is the right buy for your home — or whether, for close to the same money, you should be looking at something that handles both seasons.