HVAC sizing calculator · Sonoma & Marin

What size AC, heat pump or furnace does my house need?

Answer a few questions about your home to see the AC, heat pump or furnace size that fits it. Use it to sanity-check a quote, ours or anyone's. It's a starting point. At your home, we check all the details to confirm the right system size for your specific house.

Your home

TownSets the hottest and coldest days we size for

Heated square feetLiving space only, not the garage

Stories

Ceilings

Year builtUsed when you pick "Not sure" below

People living there

Insulation & windows

Attic insulation

Wall insulation

Under the floor

Windows

How much glass

Afternoon sun

Air leaks & ducts

How drafty is it?

Where are the ducts?

Duct condition

Check a quote (optional)

What were you quoted?

Size quoted (tons)12,000 BTU = 1 ton

Your sizing results

System size we'd look at

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Central AC–

Heat pump–

Furnace–

The load is what your house needs. Equipment is sized a bit above it, because units lose capacity on hot days and cold nights and normal sizing allows some headroom.

Where your heat goes on a cold night

Duct upgrades

Your ducts matter as much as the equipment

Ducts installed before the mid-2000s are often insulated to R-4.2 or less. California's current energy code calls for R-8 on new ducts in most of Sonoma, Napa and inland Marin, and R-6 closer to the coast.

Thin, leaky ducts in an attic or crawlspace lose heat in winter and pick up heat in summer before the air ever reaches your rooms. New, sealed, R-8 ducts are one of the best ways to improve how well any system performs and how much it costs to run.

We check your ducts on every home visit and tell you plainly whether they're worth replacing.

Want the exact number?

During a free estimate we look over the whole home, check your ducts, and show you the sizing on your proposal.

(707) 988-5858 Book a free estimate

Typical results

What size AC or heat pump does a Sonoma County home need?

Using this sizing check, a single-story 1,500 sq ft Sonoma County home built in the 1960s or 70s with its original ducts typically lands around 3.5 tons. A newer home of the same size with sealed ducts lands around 2 to 2.5 tons. Insulation, windows and ducts change the answer more than square footage does.

System size this calculator suggests, by home size and age. Single-story Sonoma County home, 8 ft ceilings, average windows and shade, 3 people, ducts in the crawlspace.
Home size	Built 1960–1979, original ducts	Built 2001–2015, sealed ducts
1,000 sq ft	2.5–3 tons	2 tons
1,500 sq ft	3.5 tons	2–2.5 tons
2,000 sq ft	4–5 tons	2.5–3 tons
2,500 sq ft	Over 5 tons (often two systems)	2.5–3.5 tons

Your home can land well above or below these. Marin homes often need a little less cooling. Use the calculator above for your own numbers, and we confirm the final size at your free estimate.

How the calculator works

We use your county's design temperatures, typical insulation for your home's age, your windows, air leaks and ducts, plus heat from people and appliances in summer. Then we pick real equipment sizes a bit above that load, the way we would on a proposal.

Why two quotes can differ

Different assumptions about insulation, windows, ducts and safety margins add up. Ask any contractor what they checked to size your system. A good one will walk you through it.

A planning guide for comparing quotes, not a final equipment selection. Design temperatures: ENERGY STAR county reference values (Sonoma 29°F / 96°F, Marin 32°F / 88°F, Napa 31°F / 98°F, San Francisco 40°F / 79°F). Coastal and hilltop homes can differ from the county figure.