Most residential heating and cooling equipment has a minimum output well above what a few hundred square feet actually needs. Getting that wrong is why so many new backyard units are either freezing, roasting, or noisy all night.
What we doADUs, garage conversions and small backyard homes, plus the main house when it comes with them
HowDuctless systems sized to a real load, sited before the walls close
WhenAt design, not at drywall — three decisions get made early or get compromised late
A backyard unit at the end of an ordinary Santa Clara lot
The core problem
Everything on the shelf is too big.
It is not a supply problem or a budget problem. It is arithmetic, and it is the single thing that separates this work from ordinary residential HVAC.
A well-built modern accessory dwelling unit is small, reasonably insulated and reasonably sealed. Its calculated heating and cooling load is correspondingly small — considerably smaller than most people expect, and often smaller than the minimum output of a conventional ducted system.
Install one anyway and the behaviour is predictable. The system reaches the thermostat in a few minutes, shuts off, sits idle, and starts again. Over a day that is a lot of starts and very little run time. Short cycling gives you uneven temperatures, poor humidity control in a space that is already small, more wear on the machine's hardest moment — the start — and a unit that is heard far more often than it is felt.
The answer is not a clever accessory. It is smaller equipment that can also turn down: a ductless system, specified at a capacity that matches the building, running long and gentle instead of hard and briefly.
What we do about it
We calculate the load from the drawings or from the finished shell — envelope, glazing, orientation, insulation — rather than applying a rule of thumb per square foot. Rules of thumb were written for older, leakier houses and they oversize a modern small unit badly.
Then we choose equipment that can operate below that number as well as at it, because a small building spends most of the year needing much less than its design load.
One honest limitation
A very small, very tight building can be genuinely difficult to keep even, no matter what is installed — a single head serving an open-plan unit with a separate bathroom and a closed bedroom door will never treat all three the same. We will tell you where those limits are before the work, and what a second head would cost, rather than leaving you to discover it in July.
What we do
Five services.
Small-unit work first, with the main house when it comes as part of the same project. Each one is written out in full on the services page.
01
ADU heating & cooling
New detached and attached units. Load calculated from the design, equipment sized to it, outdoor unit sited before the walls close, and the work scheduled into somebody else's build programme.
Single-head and multi-head heat pumps: the indoor units, the outdoor unit, the line route, the condensate, and line covers that look deliberate rather than improvised.
A different problem from a purpose-built unit: an uninsulated slab, a low ceiling, a large opening where the door was, and a wall shared with the house. Worth its own conversation.
Ductless and ducted. Diagnostic first, quote second, and a particular interest in systems somebody else oversized — because the fix for that is rarely another machine.
Ductless equipment needs different attention from ducted: the indoor blower wheel and drain pan, the filters, and the outdoor coil. Annual, written up, with photographs.
No electrical panel or subpanel work, no general contracting, no ADU design or permitting for the building itself, no roofing, no solar. We are one trade on somebody else's project and we say so.
Where the outdoor unit standsIt needs clear air on the sides the manufacturer specifies, somewhere for condensate to go, distance from bedroom windows on both properties, and it has to respect setbacks and local noise rules. On a lot with a house at the front and a unit at the back, the number of legal, practical positions is often one or two.
Two
How the lines get thereRefrigerant lines, a control cable and a condensate drain have to travel from that outdoor unit to each indoor head. Decided early, that route runs inside a wall or a chase and disappears. Decided late, it runs on the outside of a brand new building in a line cover.
Three
What electrical capacity the unit hasA heat pump needs a dedicated circuit. Whether the ADU has its own service or is fed from the main house, somebody has to have allowed for it. We do not do panel or subpanel work — we tell your electrician what the equipment needs, in writing, early enough to be useful.
One head, one small room — sized for the building rather than for a rule of thumb
How a job goes
Four steps, fitted into your programme.
Call, with drawings if you have them
Or a description of the shell. We can say a great deal from a floor plan and an elevation before anybody drives out.
Site visit
The lot, the setbacks, the neighbours' windows, the route, the panel, and what the rest of the build is doing. An hour, and no obligation.
Load calculation and a written scope
What the building needs, what we propose, where everything goes, and what your electrician has to allow for. On paper.
Two visits, usually
Rough-in before the walls close and commissioning at the end. Dates agreed with whoever is running the programme, and the permit pulled.
Working around people
Most of these jobs happen in somebody's back garden while they live in the front.
Access and parking agreed in writing before the first day, including whether we can come through the side gate and where the van goes.
The line route kept off the main house wherever the design allows it, because a line cover across the front elevation of the house you live in is a permanent decision.
Reasonable hours, and no core drilling at half past seven on a Saturday.
The yard is not a site overnight. Materials go back in the van or into the shell, and the path stays walkable.
The neighbour conversation happens early. An outdoor unit near a fence line is worth mentioning to the person on the other side of it before it arrives, not after.
The side gate, which is usually the whole logistics plan
Where we work
A tight radius, on purpose.
Small-unit work is a lot of short visits at specific points in somebody else's build schedule. That only works close to home, so we stay in the middle of the valley.
Santa Clara
San Jose
Sunnyvale
Cupertino
Campbell
Saratoga
Los Altos
Milpitas
Outside that list, call anyway — if we cannot take it on we will usually know who can.
On emergency cover
We do not advertise 24-hour service. A small shop cannot staff it honestly, and a promise that fails at two in the morning is worse than no promise.
The phone is answered from half past seven, overnight messages are returned first thing, and a unit with no heating or cooling at all with somebody living in it goes to the front of the day.
Builders and designers
If you are running the project rather than living in it, say so on the first call. We will give you the electrical requirement, the outdoor unit footprint and the rough-in window in a form you can hand to the rest of the trades, and we will work to your programme rather than ours.
Common questions
Asked on nearly every site visit.
Why does my ADU need a different kind of system?
Because it is small, and most residential equipment is not. A conventional ducted system has a minimum output well above what a few hundred square feet actually needs, so it satisfies the thermostat in minutes, shuts off, and spends the day cycling. A ductless system can be specified far smaller and can run at part load, which is what keeps a small room even rather than swinging.
When should you be involved in an ADU build?
At design, not at drywall. Three things get decided early and are expensive to change late: where the outdoor unit can legally and practically stand, how the refrigerant and condensate lines get from there to the indoor unit, and how much electrical capacity the unit has. Being called in after the walls close usually means a compromise on at least one of those.
Where does the outdoor unit go on a small lot?
That is the constraint that shapes most of these jobs. It needs clear air on the sides the manufacturer specifies, a route for condensate, distance from bedroom windows — yours and the neighbours' — and it has to respect setbacks and local noise rules. On a Santa Clara lot with an ADU at the back, that is a real design question and we settle it on the first visit rather than on install day.
Can you work while the main house is occupied?
Yes, and it is most of what we do. It means agreeing access and parking in advance, keeping the line route off the main house where possible, working within reasonable hours, and not leaving the yard as a site overnight. We say all of that in writing before the first day rather than discovering it on it.
Which areas do you cover?
Santa Clara, San Jose, Sunnyvale, Cupertino, Campbell, Saratoga, Los Altos and Milpitas. A tight radius on purpose — small-unit work is a lot of short visits at specific points in somebody else's build schedule, and that only works close to home.
Call before the walls close.
Send a floor plan and an elevation if you have them. We can answer most of the important questions before anybody drives out.
