HVAC System Replacement in Brentwood: Heating and Cooling Done as One Project

In a lot of Brentwood houses the furnace and the air conditioner went in on the same week, which means they wear out on roughly the same schedule. When one fails and the other is close behind, an HVAC system replacement handles both at once: one crew, one permit, one set of ducts opened and closed. This page shows how we price that kind of job so you can decide whether to do it in one go.

How the combined price is built

A full system quote is two halves plus what joins them.

Part of the job	Site price line
Cooling half	Most complete AC installations in Brentwood run between $6,200 and $11,500 depending on system size, efficiency tier, and whether ductwork modification is required
Heating half	Gas furnace replacement costs $4,500 to $7,500
One-system option	A complete ducted heat pump installation in a typical Brentwood Westside home runs $8,000 to $14,000 depending on system size, ductwork condition, and electrical panel capacity

Those are separate site figures, not a bundle price. Doing both halves together does not change the equipment cost, but it removes the work you would otherwise pay for twice: a second trip to the attic, a second permit, a second round of duct sealing and a second start-up. Your quote shows each half on its own lines so you can see what the house needs. If you want the pair priced for your address, send both unit ages through the whole-system quote form and we plan one visit for it.

Why the two halves belong on one quote

The indoor coil for the AC sits on top of the furnace, and both share the blower and the ducts. Replace only one, and the new half gets bolted to an old half that was sized and rated for a different pairing.

Doing them together lets us:

• Size the furnace and the AC from the same load calculation, so they fit the house as it is today.
• Match the coil to the condenser and to the blower, which is how the efficiency on the label is reached.
• Open the ducts once. If they need sealing or a resize, it happens with both units out.
• Pull one LADBS permit for the change-out instead of two.

If only one half has failed and the other is genuinely sound, we tell you that and quote the single unit. Our AC installation and heating installation pages cover each half on its own.

The ducts decide the rest of the number

The two units are the predictable part of the quote. The ducts are where houses differ.

Many Brentwood ducts were sized for heat only and are too small for the airflow a cooling coil needs. Some were added through the attic later as flex, and the runs have sagged. A new matched system pushed through a choked duct run is louder and cools the far rooms poorly.

We inspect every supply and return before we price. When the runs are sound, sealing may be all they need. When they are not, full replacement, which is what long retrofit runs and collapsed flex usually need, runs $3,200 to $7,400 and scales with the number of supplies and the distance from the air handler to the far end of the house. That goes on the quote as a separate line from the equipment. See our ductwork services for what that work involves.

Permit, testing and the new refrigerant

Replacing a furnace, an AC and ductwork is permitted work in California. In Brentwood the permit is issued by LADBS, and we handle it when the project needs it. Depending on the scope, Title 24 Part 6 can require duct sealing and a duct leakage test, verified by a third-party HERS rater who is not the installer. On a combined job that test happens once.

The new AC or heat pump will use a lower-GWP A2L refrigerant such as R-454B or R-32. The quote lists SEER2 for cooling and, on a heat pump, HSPF2 for heating, so each option is compared on the current federal ratings.

A gas furnace change-out also means checking the flue and the gas connection to SoCalGas service. California law requires carbon monoxide alarms in homes with a fuel-burning appliance, so we confirm yours are in place.

What the replacement project looks like from your side

• One visit to measure the house, inspect the ducts, check the LADWP panel and walk the condenser spot.
• One written quote before any work starts, with the cooling half, the heating half, duct work and permit as separate lines.
• One install window. Old equipment out, new equipment in, ducts sealed, both halves started and tested together.
• A walkthrough at the end so you know the thermostat and the filter location.

Gated streets and canyon roads off Mandeville and Sullivan need access planned ahead. We confirm gate codes, parking for the truck and the route to the attic when we book.

FAQ

Does replacing both at once cost less than doing them a year apart?

The equipment costs the same. You save on the repeated labor, the second permit and the second duct test, which is why the combined quote is often lower than two separate jobs.

Can I keep my gas furnace and only replace the AC?

Yes, if the furnace is sound and its blower can carry the new coil. We check that at the visit and tell you plainly.

Should I choose a heat pump instead of two units?

It depends on the house, the panel and how you want to heat. A heat pump replaces both halves with one system, and we write it next to the furnace and AC pair.

How long is the house without heat or cooling?

Only during the install window. We schedule it so the old system stays running until the crew is ready to swap.

Call (877) 702-9609 to book one visit and get your full HVAC system priced in writing by Brentwood Air.