Answer four questions and get a recommended standby-generator size in
kilowatts plus a realistic installed-cost range — unit, transfer switch,
pad, fuel hookup, electrical, and permits. It's a planning estimate, not a
quote: the final number always comes from an installer's load calculation
at your home.
Whole-house sizing is driven by square footage, because floor area tracks
the big loads — central air conditioning above all. Essential-circuits
coverage barely grows with the house: a bigger home mostly adds circuits
you've chosen not to back up. These are the bands the calculator uses,
with installed costs at the national baseline (natural gas; propane adds
a tank, roughly $1,000–$3,000, and California runs about 12% above
baseline on labor and permits):
Whole-house coverage
Home size
Generator size
Installed cost (est.)
Type
Up to 1,500 sq ft
14–18 kW
$8,000–$12,000
Air-cooled
1,500–2,500 sq ft
18–22 kW
$9,000–$14,000
Air-cooled
2,500–3,500 sq ft
22–26 kW
$11,000–$16,000
Air-cooled
3,500–5,000 sq ft
26–32 kW
$15,000–$25,000
Air- or liquid-cooled
Over 5,000 sq ft
32–48 kW
$20,000–$40,000
Liquid-cooled
Essential circuits only
Home size
Generator size
Installed cost (est.)
Type
Up to 2,500 sq ft
10–12 kW
$6,000–$8,500
Air-cooled
2,500–4,000 sq ft
12–14 kW
$7,000–$9,500
Air-cooled
Over 4,000 sq ft
14–18 kW
$8,000–$11,000
Air-cooled
Two things move a home out of its band: big motor loads (multiple AC
units, a pool pump, a large well pump, electric heat, an EV charger you
want live during outages) push it up, and load-management modules — which
shed low-priority circuits when the generator nears capacity — can pull
it down a size. Both are exactly what an installer's site-visit load
calculation settles.
Ready for real numbers?
A licensed installer will confirm the size with a load calculation and
quote the whole job — unit, transfer switch, gas work, and permits.
Tell us about your project and we'll connect you
with a qualified installer serving your area, or browse
Michigan , Texas , California , Florida installers directly.
Generator sizing questions
How accurate is this generator sizing calculator?
It puts you in the right neighborhood — close enough to budget and to
have an informed conversation with an installer. The real answer is a
load calculation, which any good installer performs during the site
visit: they add up the actual circuits you want backed up, measure the
starting surge of your AC or well pump, and check that your gas meter
can feed the unit. Treat the number here as a planning estimate, not a
quote.
What is the difference between essential-circuits and whole-house coverage?
Essential-circuits coverage backs up a chosen subset — typically the
furnace, sump pump, well pump, refrigerator, and some lights — through a
smaller transfer switch, and fits in roughly 10–14 kW. Whole-house
coverage backs up every circuit in the panel, air conditioning included,
which is what pushes a typical home to 18–26 kW. Essentials costs
less up front; whole-house means never thinking about what is on the
list when an outage hits.
What is the difference between air-cooled and liquid-cooled generators?
Air-cooled units — the standard home standby product from Generac,
Kohler, Cummins, and Briggs & Stratton — top out around
26 kW and cover the large majority of homes. Bigger homes step up
to liquid-cooled units (32 kW and up): automotive-style engines
with radiators, quieter per kilowatt, and priced like the commercial
equipment they are — installed projects commonly run well past
$20,000.
Which fuel should I choose — natural gas, propane, or diesel?
If a natural gas line reaches your home, that is usually the answer:
no tank to fill, and the generator runs as long as the utility keeps
gas flowing. Propane is the standard where gas service doesn't reach —
it needs a 250–500 gallon tank, which adds cost if you don't already
have one, and your runtime is whatever the tank holds. Diesel is a
niche for homes: liquid-cooled units, on-site fuel storage, and fuel
that needs periodic polishing — usually chosen only for very large
homes or properties where neither gas nor propane is practical.
What does the installed cost estimate include?
Everything a turnkey install involves: the generator itself, the
automatic transfer switch, a concrete or composite pad, gas or propane
piping, electrical work, permits, and commissioning. It does not
include optional extras like load-management modules, cold-weather
kits, extended warranties, or a new propane tank lease. Labor and
permit costs vary by region — the state you pick adjusts for that.
Can I install a standby generator myself?
No — and not just for safety reasons. A standby generator install
involves panel work, a transfer switch, and a fuel-gas connection, all
of which need permits and inspection, and every state we cover requires
the electrical work to be done by a licensed contractor. An improper
install can backfeed the grid and endanger utility workers. This is
exactly the job the installers in this
directory do every week.