You generally need a 15–30 kW whole house generator for most modern homes, but the exact size depends on your appliances, heating/cooling, and how much of the house you actually want powered during an outage.

Quick Scoop: What size whole house generator do I need?

Think of sizing a generator like packing for a long trip: the more “stuff” (appliances) you insist on bringing, the bigger the suitcase (generator) has to be.

Very rough kW ranges

These are ballpark numbers, not a substitute for a real load calculation, but they give you a realistic starting point:

  • Small homes or “essentials only” (lights, fridge, a few outlets, maybe gas furnace blower): 7–12 kW
  • Typical 1,500–3,000 sq ft home, most essentials + 1 small AC or heat pump: 15–22 kW
  • Larger 3,000–5,000 sq ft home, multiple HVAC units, electric oven, well/sump pump: 22–32 kW
  • Very large / high-demand homes (5,000+ sq ft, pool, hot tub, EV charging, big electric heat): 36–50+ kW

A lot of “whole house” installations for average-sized homes land around 18–24 kW because that comfortably handles one or two HVAC units plus the usual appliances.

How to actually size your generator (simple method)

The smartest way is to size for what you’ll run at the same time , not the whole panel on paper.

  1. Make a list of everything you want powered
    • Must-haves: fridge/freezer, lights, Wi‑Fi, furnace blower, well/sump pump, medical gear, garage door, maybe a small AC.
    • Nice-to-haves: electric oven, dryer, big AC, hot tub, pool equipment, EV charger.
  1. Find the wattage for each item
    • Check labels (nameplates) or manuals.
    • Use typical numbers when you can’t find it (for example: fridge ~600 W running, 1.5–2 ton AC ~3,500–5,000 W running).
  1. Account for “starting watts”
    • Motors and compressors (AC, fridge, well pump) can need 2–3× their running watts for a split second when they start.
 * Some guides suggest sizing the generator to roughly **double** your running load to comfortably handle those surges.
  1. Add a safety margin
    • After you add up your expected wattage, add 20–25% on top for safety and future appliances.
  1. Convert watts to kW
    • Divide your final watts by 1,000 (for example, 18,000 W ≈ 18 kW).

Example: A 2,000 sq ft home planning to run a fridge, lights, gas furnace blower, Wi‑Fi, a well pump, and a 2–3 ton AC might easily land in the 15–20 kW range once you include starting watts and safety margin.

Home size vs. generator size (rule-of-thumb table)

Remember, this is only a guideline. Efficient vs. older homes, gas vs. electric heat, and number of AC units make a big difference.

html

<table>
  <thead>
    <tr>
      <th>Home size & usage</th>
      <th>Typical generator size</th>
      <th>What it usually covers</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>< 1,500 sq ft, essentials only</td>
      <td>7–10 kW[web:1][web:3]</td>
      <td>Lights, fridge, gas furnace blower, a few outlets</td>
    </tr>
    <tr>
      <td>1,500–2,500 sq ft, modest use</td>
      <td>10–15 kW[web:3][web:5]</td>
      <td>Essentials plus some kitchen loads, maybe small AC</td>
    </tr>
    <tr>
      <td>2,000–3,000 sq ft, typical “whole house”</td>
      <td>15–22 kW[web:1][web:3]</td>
      <td>Most appliances, 1 AC/heat pump, pumps, electronics</td>
    </tr>
    <tr>
      <td>3,000–5,000 sq ft, higher demand</td>
      <td>22–32 kW[web:3]</td>
      <td>Multiple HVAC units, oven, pumps, most of the house</td>
    </tr>
    <tr>
      <td>> 5,000 sq ft or many luxury loads</td>
      <td>36–50+ kW[web:3]</td>
      <td>Large homes with pool, hot tub, EV charging, big electric heat</td>
    </tr>
  </tbody>
</table>

Forum-style tips and “gotchas” people run into

Real-world discussions often hit the same themes:

  • Don’t size by “average daily kWh”
    • People try to take their utility bill and convert it; that doesn’t work because the generator must handle peak load, not daily total.
  • Total harmonic distortion (THD) matters
    • High THD from cheap generators can be rough on sensitive electronics; many users specifically look for low-THD inverter or standby units.
  • Budget vs. convenience
    • It’s common to discover the generator itself is only half the cost once you add transfer switch, gas line, pad, permits, and electrician time.
  • Square footage can mislead
    • An efficient 2,500 sq ft home with gas heat may need less generator than an older 1,600 sq ft home with all-electric everything.

You’ll also see a lot of people saying they thought they needed a massive generator, then realized that managing which big loads run at the same time let them use a smaller, cheaper unit.

How to get a more precise answer for your house

If you want a very accurate “what size whole house generator do I need” answer for your specific situation:

  1. List all loads you truly care about (especially HVAC, water pumps, medical gear).
  2. Grab the labels (or photos of labels) on:
    • AC/heat pump condensers and air handlers
    • Well/sump pumps
    • Electric range, water heater, dryer if you expect to use them.
  3. Total the running watts and estimate starting watts
    • Assume 2–3× running watts for major motor/compressor loads if you don’t have exact surge numbers.
  1. Add 20–25% margin and convert to kW.
  1. Run it by a licensed electrician or generator installer
    • Many companies will do a quick load calculation and site visit, especially if they’re quoting the install.

If you tell me:

  • Your approximate square footage
  • Gas vs. electric heating
  • Number and size of AC units
  • Whether you have a well, sump pump, or big electric appliances (dryer, oven, water heater),

I can walk through a rough load estimate and suggest a more tailored kW range. Meta description (SEO):
Wondering what size whole house generator do I need? Learn the typical 7–50 kW ranges, how to calculate your home’s wattage, forum-tested tips, and what really matters beyond square footage. Information gathered from public forums or data available on the internet and portrayed here.