How do you size a heat pump for a large two-story Lafayette house?
We run Manual J floor by floor with real window areas and insulation. Often upstairs drives the cooling load, so we recommend zoning or a second system instead of one big unit.
Residential HVAC · Lafayette, CA
Residential HVAC & Heat Pumps in Lafayette, CA
Lafayette houses are large, multi-level and often built on a slope. We design and install heat pump systems around that: load calculations by floor, duct design that fits additions, and equipment placed where the lot allows.
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
Project fit
What we do for Lafayette homeowners
Six common scopes for homes in Lafayette, from swapping a tired furnace and AC to planning the mechanical system for a full addition.
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Big homes
Two-system and zoned replacement
Upstairs and downstairs rarely want the same thing. We split large Lafayette floor plans into zones or separate systems so neither level is chasing the other.
Replacement & conversion -
Conversion
Gas furnace to heat pump
Remove the gas furnace and AC, cap the gas line and add the heat pump, electrical work and condensate path in one permit.
Gas-to-heat-pump -
Ducted
Ducted heat pumps for ranches and split-levels
Many 1950s and 60s Lafayette homes have usable attic or crawlspace ducts. We test them, size new returns and replace only the runs that fail.
Ducted heat pumps -
Ductless
Ductless heads for bonus rooms and additions
A room over the garage or a converted office often cannot be reached by the old trunk. One ductless head solves it without touching the main system.
Ductless options -
Design team
Mechanical design for remodels and rebuilds
We give architects and builders a Manual J, equipment locations and chase sizes early enough to fit into framing and Title 24 documents.
HVAC for remodels -
Air quality
Smoke-season filtration and ERV
Deep media filters and balanced ventilation let Lafayette homes stay sealed when wildfire smoke settles into the valley.
Ventilation & IAQ
A comparable East Bay retrofit
Whole-home heat pump remodel
View project →
High-end residential remodel
Hearst Remodel
This is a Berkeley job, shown here because it follows the same steps we use in Lafayette: a room-by-room load, equipment placement on a tight exterior, and field coordination with the remodel team.
- 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 published remodel scope — location, photos, and full details on the project page.
View projectLocal projects
Heat pump & HVAC installs for Lafayette homes
Recent installs by the 3rdGen crew that serves Lafayette: ducted and ductless heat pumps, air handlers and ductwork.
Built around the lot and the floor plan
In Lafayette, the slope and the square footage decide how the system is laid out
A Lafayette house can sit on a flat lot near downtown or perch on a ridge above Happy Valley. Both may be 3,000 sq ft, and they need different plans. Slope changes where the outdoor unit goes, how condensate drains and how long the line set runs.
We start with Manual J for each floor, then use Manual S to pick equipment at Lafayette’s 91°F summer design day. Manual D comes last and tells us whether existing ducts can carry the airflow.
Wide daily temperature swings mean attic spaces get very hot in the afternoon. Ducts in those attics lose a lot of capacity, which is why we check insulation and leakage before reusing them.
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Hillside lots
Equipment pads, wall brackets and line-set routes get tested against the real grade. Sometimes the best outdoor unit location is not the closest one.
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Two-story additions
A second story added to a 1950s ranch usually shares a duct system it was never sized for. We recalculate loads with the addition and fix returns first.
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Large glass and vaulted rooms
West-facing glass and tall ceilings add real cooling load. Manual J counts every window by orientation, not just a square-foot guess.
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Wildfire smoke
We leave room for a thicker filter and discuss ventilation options early, since retrofitting them later is harder.
Mechanical permits in Lafayette are handled by the City Building Division. If the lot is on a hillside or the job comes with an addition, ask about planning review early so the equipment location is settled before submittal.
Heat pump design in Lafayette
Lafayette houses are big, tall and spread over slopes, so one thermostat rarely fits
Between the flat streets near the BART station and the ridges above Happy Valley, Lafayette has everything from small 1950s ranches to multi-level homes over 4,000 sq ft. The right heat pump plan changes with each. We run Manual J on the actual house, then decide how many systems and zones it needs.
Design climate · Title 24 Climate Zone 12
- Winter design temp
- 32°F
- Summer design temp
- 91°F
Lafayette sits inland of the Berkeley hills, so winter nights drop to about 32°F and summer afternoons design out around 91°F. Cooling load is often the bigger sizing driver, with a wide daily swing of roughly 30 degrees. Heat pumps handle this well, and the mild winter lets us size for cooling without worrying about cold-climate capacity.
ACCA Manual J design data · Lafayette (ACCA micro-climate)
The houses we plan around in Lafayette
Many Lafayette homes went up in the 1950s through 1970s as ranches and split-levels, then grew with second-story additions. Those additions are where comfort problems start: an upstairs run fed from an undersized trunk, or a bonus room over the garage with no return at all.
On the hillsides, homes step down a slope. Crawlspaces vary in height from one end of the house to the other, and the best outdoor unit location is often a side yard or a retaining-wall ledge rather than the usual back-corner pad.
Large floor plans, vaulted great rooms and big west-facing glass push cooling loads well above what the old furnace and AC pair delivered. We often find the existing equipment was sized years ago, before windows or insulation changed.
Splitting a big house into zones
A two-story Lafayette house usually wants at least two zones or two systems. Upstairs bedrooms gain heat in the afternoon while the ground floor stays cool. We run Manual J floor by floor so you can see which level drives the tonnage.
Manual D for additions and long runs
Second-story additions often hang on ducts that were never designed for them. We calculate the friction rate for each run, check return sizing, and say plainly when a trunk needs to be replaced instead of reused.
Manual S on a hot day, not a cold one
At a 91°F design day with a dry-bulb swing this wide, we check cooling capacity at the real outdoor temperature, not the nameplate. Variable-speed equipment is the usual choice for the part-load hours that make up most of the year.
Smoke and filtration
Lafayette is next to wildland, and smoke seasons are real. When we design the air handler, we leave room for a deep media filter and look at adding ERV ventilation so the house can stay closed on bad-air days.
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Multi-zone and dual-system replacement
Two ducted heat pumps, or one ducted plus a ductless head for a problem room, instead of one oversized system.
Replacement & conversion → -
Ducted heat pump design and install
Central heating and cooling that reuses good ducts and replaces the bad ones, backed by a written duct design.
Heat pump installation → -
Manual J for architects and builders
Load reports ready for plan check on additions, remodels and rebuilds, delivered before framing is finalized.
Manual J load calculations → -
Remodel and addition mechanical
Equipment spaces, chases and ceiling heights worked out with your design team while the plans can still change.
HVAC for remodels → -
Filtration and fresh-air ventilation
MERV 13 or better filtration and ERV/HRV options for homes that want cleaner indoor air in smoke season.
Ventilation & IAQ → -
Rebates and financing guidance
We tell you which incentives and financing options apply to your scope when we quote it.
Rebates → -
Financing a large project
Options for spreading the cost of a whole-home conversion over time.
Financing →
Permits, MCE and incentives in Lafayette
Mechanical permits for Lafayette homes go through the City of Lafayette Building Division. Hillside lots and larger additions can bring separate planning review, so we ask about the lot and any other scope before we price the permit work.
Lafayette receives electricity generation through MCE Clean Energy, with PG&E handling delivery and billing. Heat pump rebates from TECH Clean California, BayREN and utility programs open and close over time, so we check current availability instead of promising an amount.
Around Lafayette
Downtown and the BART-side streets, Burton Valley, Happy Valley, the Reservoir area and the ridges above, along with Orinda, Moraga and Walnut Creek next door.
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 reviewsHow a Lafayette job runs
From the first walkthrough to a commissioned system
Large Lafayette houses reward planning. We spend the time up front on loads and ducts so the install itself goes in cleanly.
01 — Walkthrough
We tour the house, attic and crawlspace, note the slope and exterior options, and ask what rooms bother you.
02 — Manual J by floor
Heating and cooling loads calculated for each level and room, using actual windows, insulation and orientation.
03 — Manual S and zoning
Equipment chosen against the load at Lafayette design temperatures, with a recommendation on one system, two systems or zones.
04 — Manual D and permit
Duct layout sized with friction-rate math, then the permit package for the City of Lafayette Building Division.
05 — Installation
Removal, new ducts, line sets, electrical and equipment set, sequenced so the house is not without comfort longer than needed.
06 — Commissioning
Airflow, charge and thermostat zoning checked, inspection passed and a clear handoff on how to run the system.
Finished, not just installed
What a Lafayette heat pump job includes beyond the equipment
Big houses mean more pieces: second air handler, new returns, a bigger panel or a subpanel, and condensate routing on a slope. We plan them together so no trade is waiting on another.
We start up every system, measure airflow and walk you through the controls before we leave.
Tell us about the project-
Gas shutoff and removal
Furnace, coil and old condenser taken out, gas capped to code.
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New duct work
Returns added and trunks replaced where the design calls for it.
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Electrical capacity
Panel or subpanel work for the heat pumps and any future loads.
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Commissioning
Airflow, charge and zoning verified and shown to you.
Cost
What a Lafayette heat pump project costs, and what pushes it up or down
The biggest swing in Lafayette is house size and layout. One system or two, new returns or reused ducts, a flat pad or a retaining-wall ledge, and how much panel work is needed each change the scope more than the brand of equipment.
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 $8k–$15k Zone count, head type, line-set routing, and whether the ADU shares the main house or stands alone
Electrical panel upgrade, when required $8k–$10k+ Service size, meter location, utility requirements and site conditions
Complex whole-home and design-build projects can exceed these ranges. Rebates and incentives may reduce your net project cost.
Project inquiry
Planning HVAC work in Lafayette?
Tell us about the house, how many levels it has, what you want to replace and whether an addition is on the way. Plans help if you have them.
- 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.
Project teams
Working alongside your architect and builder
On Lafayette additions and rebuilds, we can hand your designer a load calculation, equipment dimensions and chase locations before the plans are finalized, so mechanical does not fight the framing later.
We work with design teams in Lafayette and the rest of Lamorinda, 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.
Start a residential project
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
Questions we hear from Lafayette homeowners about size, slope, ducts and permits.
Can you reuse the ducts in my 1960s Lafayette ranch?
Sometimes. We test leakage, check insulation and measure the trunks and returns against the new airflow. If they pass, we keep them. If not, we replace only what fails.
Our house is on a steep lot. Where does the outdoor unit go?
Options include a side-yard pad, a wall bracket or a ledge. We weigh line-set length, condensate drainage, clearances and noise toward neighbors before choosing.
Who provides my electricity generation in Lafayette?
MCE Clean Energy supplies generation and PG&E delivers it. Your rate and any heat pump rebate can depend on that, so we check current programs when scoping.
Do I need a panel upgrade for a heat pump?
Not always. A load calculation of your existing panel shows spare capacity. Whole-home conversions with an EV charger or water heater sometimes need a subpanel.
Can you design HVAC for our remodel before the plans are done?
Yes, and earlier is better. A Manual J with equipment locations lets your architect reserve space in framing and ceilings and supports Title 24 compliance documents.
What about wildfire smoke?
We can design for higher-MERV filtration and add ventilation so the home can stay closed during smoke events. It is easier to plan with the system than to add later.
Nearby service areas
Heat pump and HVAC design near Lafayette
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.