Ducted Air-Source Heat Pump
Installation in San Francisco
Your home already has ductwork — but that doesn't mean any heat pump will work in it. SF's older forced-air systems were designed for heating only. We test, size, and upgrade your ducts before installing, so your new system performs the way it should from day one.
The Hidden Problem with SF's Existing Duct Systems
Most San Francisco homes with existing ductwork have a system that was designed — and sized — for a gas furnace, not a heat pump. The difference matters more than most homeowners realize.
If your home was built in the 1960s through 1990s with a gas forced-air furnace, there's a good chance it has ductwork. But there's an equally good chance that ductwork is undersized for a heat pump — and installing one without addressing this will leave you with a system that's inefficient, noisy, and unable to reach the temperatures you set.
Here's why: gas furnaces produce heat at very high temperatures — often 140°F or hotter at the supply register. Because the air is so hot, you don't need much of it to heat a room. Duct systems designed for gas furnaces move a relatively small volume of air at high temperature. Heat pumps work differently. They produce warm air at lower temperatures — typically 90–110°F — and compensate by moving much more air volume. A duct system that was fine for your old furnace may only have the capacity to move 60–70% of the airflow your new heat pump needs.
The result? High static pressure in the system. The heat pump's blower works harder than it should, wearing out faster and consuming more electricity. Supply registers whistle. Some rooms never quite reach the set temperature. The system short-cycles. In short: you've paid for a high-efficiency system and you're not getting high-efficiency performance.
Every ducted heat pump installation we do begins with a thorough duct assessment. We measure static pressure at multiple points, calculate total effective length, inspect every supply and return register, and use an airflow hood to verify actual delivery. Then we give you a clear picture of what modifications — if any — are needed before we install.
What our duct assessment covers:
Static Pressure Testing
We measure total external static pressure (TESP) and compare it against the heat pump manufacturer's maximum rating. Anything over 0.5 inches of water column typically requires duct modifications.
Return Air Capacity
Return air is the most commonly undersized component in SF homes. We check every return grille size, the return plenum dimensions, and whether the system needs an additional return pathway.
Supply Register Sizing
We verify that each supply register can deliver the correct CFM for that room's heat load, per Manual D calculation. Undersized registers cause pressure and noise problems.
Duct Leakage Evaluation
SF homes with duct systems in attics or crawlspaces often have 15–30% duct leakage. We identify disconnected joints, failed mastic, and unsealed boots — each is wasted energy and capacity.
Plaster & Access Assessment
When duct modifications are needed in a home with plaster ceilings, we plan the least invasive access points. Our crews are trained specifically to open and patch plaster without visible damage.
Working with Plaster Ceilings: Our Approach
San Francisco has tens of thousands of homes with original plaster-over-lath ceilings. They're beautiful, they're solid, and they're notoriously difficult to work with. Unlike drywall, which can be cut with a utility knife and patched invisibly, plaster cracks under vibration and doesn't forgive imprecise cuts.
Cracks in plaster don't just stay where you cut. Vibration from a rotary saw can travel through the lath network and cause cracks to radiate outward across an entire ceiling panel. We've seen other contractors' work where a 6-inch access hole resulted in cracking across three feet of otherwise perfect plaster.
Our technique is different:
- We use oscillating multi-tools, not rotary saws, for all plaster cuts
- We score the cut line deeply before any full-depth cutting begins
- We brace the surrounding plaster field before removing the cut section
- When possible, we route duct modifications through attic or crawlspace access to avoid ceiling penetrations entirely
- Any patch work is done with matching plaster — not drywall compound — so the repair holds and blends
Systems We Install
We work with all major heat pump manufacturers and can recommend the right system for your home's duct capacity, square footage, and efficiency goals. For most SF homes, we favor variable-capacity (inverter-driven) systems that modulate output to match the load — quieter, more efficient, and more comfortable than single-stage units.
Single-Stage Ducted Heat Pump
On/off operation. Most affordable upfront. Works well in smaller SF homes with good duct systems and modest loads.
Two-Stage Ducted Heat Pump
Runs at low or high capacity. Better efficiency and comfort than single-stage; a good mid-range option for most SF homes.
Variable-Capacity Inverter System
Continuously adjusts output from 30% to 120% of rated capacity. The gold standard for comfort and efficiency in SF's variable climate.
Ducted + Ductless Hybrid
Ducted system for the main living areas; mini-split units for rooms with poor duct access. Increasingly common in SF's complex multi-story homes.
Ducted Heat Pump FAQ
Start with a Free Duct Assessment
We'll measure your duct system, identify any modifications needed, and give you a complete quote — equipment and ductwork — before any commitment.