Can a heat pump use the ducts from my old San Leandro furnace?
Sometimes. We test static pressure, check duct sizes and look for leaks. Many older systems were designed for heating only and need larger returns or new runs to handle cooling airflow.
RESIDENTIAL HVAC · SAN LEANDRO, CA
Residential HVAC & Heat Pumps in San Leandro, CA
We replace aging gas furnaces and AC units in San Leandro homes with properly sized heat pumps. The work starts with a Manual J load calculation and a hard look at the ducts, because the equipment is only as good as the air it moves.
Remodels · Retrofits · Heat Pumps · Multi-Zone Systems
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- Mitsubishi Electric Diamond Contractor
- C-20 + C-36 Licensed & Bonded
- Serving the Bay Area since 2015
San Leandro scopes
Heat pump work for San Leandro houses
Most of our San Leandro conversations begin with an old furnace, uneven rooms or no cooling. These are the jobs that solve those.
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Conversion
Gas furnace and AC replacement
A ducted heat pump replaces both furnace and AC, with the gas line capped and the panel checked in the same permit.
Replacement & conversion -
Ducts
Hot-and-cold-room fixes
New returns, resized runs and balanced registers for houses where the far bedroom never gets comfortable.
Ducted heat pumps -
New AC
Adding cooling to a heat-only house
Heat pump cooling for houses that only ever had a furnace, designed so the ducts can handle the extra airflow.
Heat pump installation -
ADU
Garage conversions and rear units
A single-zone heat pump sized to a converted garage or detached unit, with the load report for the permit.
ADU heating & cooling -
Remodel
Additions and room expansions
Supply and return paths for new rooms planned with the framing so the system is balanced afterward.
HVAC for remodels -
Design
Load-calculated sizing
We size each system we install from a Manual J, so the proposed size is backed by numbers.
Manual J load calculations
Reference project
Whole-home heat pump remodel
View project →
High-end residential remodel
Hearst Remodel
This job was in Berkeley, not San Leandro. We show it as an example of planning refrigerant routing and equipment in an existing house, as in many San Leandro retrofits.
- Home type
- Existing home, remodel for sale
- System
- Fujitsu multi-zone ductless heat pump
- Mechanical scope
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- · Six indoor wall units
- · Two outdoor units
- · Wall-mounted outdoor brackets
- · Refrigerant routing and field coordination
Challenge
- Existing older home with limited equipment placement options
- Outdoor units required side-yard wall bracket mounting
- Finish-sensitive interior installation
- Coordination with the general contractor’s remodel schedule
3RDGEN scope
- Six-zone ductless heat pump installation
- GC-led remodel coordination
- Permit and inspection support
- Startup as part of the completed remodel scope
Outcome
The six-zone Fujitsu ductless system was installed, permitted, inspected, and completed as part of the home’s remodel-for-sale scope — delivering zoned heating and cooling without a conventional ducted retrofit.
Representative example from a Berkeley, CA remodel, not a project in this city. Photos and full details on the project page.
View projectLocal projects
Recent 3rdGen work near San Leandro
Real jobs our own crew designed and installed. Street names only — we keep clients' addresses private.
- Echo Ln, Piedmont · 2024
Ductless Mitsubishi heat pump, permit finaled
Mitsubishi ductless heat pump system replacing gas heat, installed and finaled with the City of Piedmont. Homeowner left a 5-star review.
Mitsubishi Diamond Contractor → - Echo Ln, Piedmont · 2026
Gas furnace out, heat pump water heater in
Removed the old gas furnace, crawlspace asbestos abatement, new 240V circuit and a 58-gallon LG heat pump water heater (3.93 UEF) under a Piedmont permit.
Heat pump installation → - Arch St, Berkeley · 2026
Whole-home mechanical with ventilation
Full mechanical scope for a whole-house renovation: heat pump heating and cooling, new supply and return ducting, and dedicated ventilation ducting coordinated with the GC.
Full system replacement → - Capistrano Ave, Berkeley · 2026
60k Mitsubishi multi-zone, mixed indoor units
Mitsubishi 60k multi-zone with branch box feeding a 12k slim ducted unit, an 18k vertical air handler and 9k one-way ceiling cassettes, with fabricated return plenums.
Mitsubishi Diamond Contractor →
San Leandro housing
Most San Leandro houses have a heating-only duct system
A typical San Leandro house has a gas furnace in the garage or hall closet, ducts in the attic or crawlspace, and a few supply registers with few returns. It was built for heat, not cooling. Dropping a heat pump on those ducts without redesigning them is the common mistake.
We test and measure first. Where the ducts hold up, we reuse them. Where they do not, we replace the weak sections and add returns, so the new system is quiet and the rooms even out.
San Leandro’s current planning documents state that more than 60% of its housing stock was built before 1980.
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Heating-only ducts
Small supply runs and few returns limit cooling airflow. We size ducts for the new equipment rather than the old furnace.
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Garage furnaces
A heat pump air handler can often take the same spot, which saves routing but still needs a condensate path and a clear service area.
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Older panels
Many 1960s and 1970s panels are tight. We calculate capacity before choosing equipment.
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Flats versus hills
Upper San Leandro addresses see warmer summer afternoons than the flats, which changes the cooling design.
HVAC design in San Leandro
San Leandro’s post-war bungalows are a good fit for a ducted heat pump, if the ducts are right
San Leandro has a lot of one- and two-story houses from the 1940s through the 1970s, with central gas furnaces, attic or crawlspace ducts and no real cooling. The equipment is often at the end of its life and the ducts are often undersized. That makes it a city of furnace-to-heat-pump conversions, and the duct system is half of the work.
Design climate · Title 24 Climate Zone 3
- Winter design temp
- 35°F
- Summer design temp
- 80°F
ACCA lists San Leandro at 35°F for winter and 80°F for summer. Houses in the hills east of the freeway match the Upper San Leandro entry instead: still 35°F in winter but 84°F in summer. Both show a daily swing around 22°F, which means cool nights and warm afternoons.
ACCA Manual J design data · San Leandro (micro-climate); Upper San Leandro for hill addresses
What we usually find in a San Leandro house
San Leandro’s planning documents state that more than 60% of its housing stock was built before 1980. Expect single-story stucco ranches and bungalows on slab or short crawlspaces, many with floor or wall furnaces replaced decades ago by a central unit in the garage or hall closet.
Ducts are commonly flex or sheet metal in the attic, with few returns. Rooms at the far end of the run run cold in winter and hot in summer. Adding cooling by simply bolting an AC onto the old ducts often reveals the problem.
Panels from the 1960s and 1970s are often 100 amps or less. A heat pump, an EV charger and a gas-to-electric range may not all fit.
Duct testing before reuse
We measure static pressure and look at duct size before deciding to keep any of the old system. Many attic duct systems in San Leandro homes were designed for heating only and cannot move the airflow cooling requires.
Manual J with attic and slab details
Slab floors, attic insulation depth and window age make a bigger difference to loads than square footage. We collect those on site and compute each room.
Manual S for hill versus flats
A house in the flats near the bay and a house in the hills at the Upper San Leandro entry have different cooling loads. We size to the right one, and that can change the system by a half ton or more.
Manual D and returns
Adding properly sized returns often does more for comfort than changing the unit. We design supply and return together and balance each room.
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Furnace and AC to heat pump
One heat pump replaces both gas heat and cooling, with ducts corrected during the same job.
Replacement & conversion → -
Duct redesign and sealing
New trunks, returns and registers sized to a Manual D for homes with hot and cold rooms.
Heat pump installation → -
Load calculations
A Manual J for each replacement or addition we install, done before equipment is chosen.
Manual J load calculations → -
Garage and backyard ADUs
A dedicated heat pump for a converted garage or detached unit on San Leandro’s typical lots.
ADU heating & cooling → -
Addition and room-expansion HVAC
Extra heating and cooling capacity added with the framing, not on top of it.
HVAC for remodels →
Permits, power and incentives in San Leandro
Mechanical and electrical permits for heat pump installations go through the City of San Leandro’s building services. We prepare equipment data, Title 24 documents and the load calculation, and we book the inspections.
San Leandro customers receive generation from Ava Community Energy with PG&E delivering. Incentives such as TECH Clean California, BayREN and utility programs change, and eligibility depends on the equipment and your household. We check what is open before you commit, and our rebates page explains the basics.
Where we work around San Leandro
Bay-O-Vista, Washington Manor, the Estudillo Estates and downtown areas, the hill neighborhoods above the freeway, and nearby Oakland, Hayward and Castro Valley.
Homeowner reviews
Trusted by Bay Area Homeowners
5.0
5 out of 5 stars from 207 Google reviews 207 Google reviews
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Mitsubishi mini-split installed with outstanding care. Indoor and outdoor units done right. High efficiency meant a meaningful federal tax credit too.
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Devin and his crew did a fantastic job installing AC for our whole house. High quality Mitsubishi equipment and a clean installation throughout.
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Devin is meticulous, methodical, and knowledgeable. Professional crew and a heat pump install we trust completely.
Photos from the installs above
Read all 207 reviewsSan Leandro project steps
How a San Leandro conversion runs
A furnace swap is quick on paper and easy to get wrong. We use a fixed sequence so the numbers come before the equipment.
01 — Walk-through and duct check
We look at the furnace, attic or crawlspace, supply and return layout, the panel and how each room feels now.
02 — Manual J loads
Room loads calculated with San Leandro design conditions, adjusted if your address is in the hills.
03 — Manual S selection
Heat pump capacity chosen to the load, not to the nameplate on the old furnace.
04 — Manual D duct design and permit
Duct and return layout drawn to the airflow each room needs, with documents submitted to the City.
05 — Installation
Furnace removed, gas capped, new equipment installed, ducts sealed and electrical done.
06 — Commissioning and balance
Airflow per room, charge and controls verified before the final inspection.
Conversion checklist
A San Leandro furnace swap should leave you with better ducts
We remove the old furnace, cap and test the gas line, replace the failing sections of duct, and add returns where needed. Panel and circuit work is planned at the start.
We finish by measuring airflow, checking refrigerant charge and balancing registers.
Tell us about the project-
Duct test
Static pressure and leakage checked before any duct is kept.
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Equipment swap
Furnace and AC out, heat pump in, with the gas line capped.
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Distribution fixes
Returns added and undersized runs replaced as designed.
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Balance and handoff
Room airflow measured and the system explained to you.
Cost
What goes into the price of a San Leandro conversion
The equipment gets the attention, but in San Leandro the price is driven by what has to happen to the ducts, the panel and the gas line. A house that needs new returns and a service upgrade costs more than one with good ducts and a spare breaker.
Scope Typical 3rdGen Project Range What drives it
Ducted heat pump, existing ducts usable $20k–$30k Equipment tier, capacity, controls, condenser location and access
Ducted heat pump + duct repair or resizing $25k–$45k Amount of ductwork replaced, crawlspace or attic access, return-air changes
Ductless multi-zone, 3–4 heads $25k–$40k Head type, line-set length, routing, concealment and finish conditions
Whole-home ducted + ductless combination $40k–$80k+ Multiple systems, zoning, ductwork, filtration, ventilation and architectural coordination
New construction system $20k–$50k+ Building size, system count, Title 24/design requirements and coordination with the build
ADU system $10k–$15k Zone count, head type, line-set routing, and whether the ADU shares the main house or stands alone
Electrical panel upgrade, when required $10k+ Service size, meter location, utility requirements and site conditions
Prices as of November 2026. Complex whole-home and design-build projects can exceed these ranges. Rebates and incentives may reduce your net project cost.
San Leandro estimates
Tell us about your San Leandro house
Share what you have now, the age of the furnace, the rooms that never feel right and whether you want cooling. Photos of the furnace area and panel help.
- Reviewed by a project lead, not a dispatcher
- We tell you if your scope is not a fit for us
- No high-pressure in-home sales appointment
Project Inquiry
Inquiry Sent
Thanks — your project details are on their way to 3rdGen. We’ll review them and follow up about the next step.
Working with your contractor
We work with your builder or directly with you
If you are adding a room or remodeling, we coordinate with your contractor on duct paths and equipment so the work matches the framing schedule.
We work with project teams in San Leandro and the surrounding East Bay, or directly with homeowners.
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Architects
Mechanical systems coordinated around architecture, ceiling conditions, equipment locations, routing, and finish requirements.
Explore HVAC for architects -
General Contractors & Builders
Clear scope, scheduling, rough-in coordination, submittals, inspections, startup, and project handoff.
Explore HVAC for builders & GCs -
Mechanical Engineers
Field execution, equipment selection, controls coordination, submittals, installation, and commissioning aligned with the mechanical design.
Explore engineering coordination -
Homeowners
Already assembling your own project team? We can take ownership of the mechanical scope and coordinate directly with the other professionals involved.
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Mitsubishi Electric
Proud Mitsubishi Electric Diamond Contractor
As a Mitsubishi Electric Diamond Contractor, we design and install ducted, ductless, and multi-zone systems for Bay Area homes, with factory-trained crews and longer warranty options on qualifying residential installs.
Mitsubishi is not automatically the answer to every home. We start with what the project requires and recommend the system that makes sense.
12 Year Parts &
Compressor Warranty
12-year warranty
Extended parts & compressor coverage on qualifying Diamond installations.
Factory-trained crews
Ongoing manufacturer training on the latest hyper-heat systems.
Priority support
Direct factory escalation if anything ever needs attention.
FAQ
Common Questions
Straight answers about ducts, panels and sizing for San Leandro homeowners.
Why are some rooms in my house always cold or hot?
It is usually distribution: long runs, too few returns, or a sunny exposure. A new Manual J and Manual D can fix it, often without changing the equipment size.
My house is in the San Leandro hills. Does that matter?
Yes. ACCA data for Upper San Leandro shows a warmer summer design than the flats. We size cooling accordingly and look at how far the hill addresses diverge.
Can I add air conditioning to a house that only has a furnace?
Yes, with a heat pump. We check duct capacity and electrical service first so the new system works as designed.
Do I need a permit in San Leandro for a heat pump?
Yes. We submit the mechanical and electrical permits and schedule the inspection.
Who provides electricity in San Leandro and are there rebates?
Ava Community Energy is the default generation provider, with PG&E delivering. Rebates such as TECH Clean California and BayREN change over time, so we confirm what is available when we quote. We do not promise amounts.
Will my older panel handle a heat pump?
Often yes, sometimes with changes. We calculate it before ordering equipment so it does not become a surprise.
Nearby service areas
Heat pump and HVAC design near San Leandro
Project Inquiry
Inquiry Sent
Thanks — your project details are on their way to 3rdGen. We’ll review them and follow up about the next step.