What Size Generator Do You Need for Your Northern Virginia Home?

Start with what you want covered, not the home's square footage

Generator sizing is really a question about scope: do you want to keep the essentials running (refrigerator, sump pump, well pump, some lighting and outlets) or do you want the whole home to function normally, including central air conditioning, which is one of the largest loads in a typical house? These two goals lead to very different generator sizes, regardless of square footage.

Typical sizing tiers

These are general starting points — an accurate size comes from an actual load calculation of your specific panel and appliances:

• 7-10kW: Essential circuits only — refrigerator, sump pump, some lighting and outlets, no central air.
• 10-13kW: Essential circuits plus a well pump and a window or single-zone AC unit.
• 16-20kW: Most central air systems for an average-size home, plus everything above.
• 20kW+: Larger homes with multiple HVAC zones, well pumps, and a goal of near-normal operation during an outage.

Portable vs. standby changes the sizing conversation too

A portable generator connected through a manual transfer switch or interlock kit is typically sized toward the smaller end of these tiers, since it's meant to cover priorities during an outage rather than run everything. A permanently installed standby generator, especially one paired with an automatic transfer switch, is more often sized for broader or whole-home coverage since it's designed to start itself and run for extended periods without a homeowner managing it.

Permits and HOA approval in Northern Virginia

Standby generator installations typically require a permit from your local jurisdiction (Fairfax County, Arlington County, or the applicable city), covering both the electrical transfer switch work and, often, the generator's gas line connection if it's natural-gas fueled. If you're in an HOA or cluster-association community — common in Reston, Herndon, and similar communities — exterior equipment like a standby generator unit may also need association approval before installation, separate from the permit itself. It's worth checking both requirements before finalizing a generator purchase.

Why the sizing conversation should happen before you buy

Buying a generator sized for the wrong scope is an expensive mistake to fix afterward. Before purchasing, it's worth having an electrician review your panel and priority circuits — this also surfaces whether a transfer switch alone will do the job or whether other electrical work is needed first.