What size generator for a 3,500 sq ft house?
Essentials for a 3,500 sq ft house (fridge, furnace fan, lights, TV, phones) run about 2,200 watts and fit a 3,500W portable. Add the typical 4.5 ton central AC and you need a 9,500W portable; full standby sizing is 14 kW with gas appliances, past air-cooled sizes all-electric. The tiers below are the whole decision.
Portable tiers at 3,500 sq ft
| What you power | Running | Peak | Buy |
|---|---|---|---|
| Essentials: fridge, furnace fan, lights, TV, phones | 2,200 W | 3,750 W | 3,500W portable |
| Comfort: essentials + sump pump + window AC | 4,450 W | 6,000 W | 6,500W portable |
| Essentials + 4.5 ton central AC | 7,600 W | 11,380 W | 9,500W portable |
Standby classes at 3,500 sq ft
Rule-of-thumb demand from the whole-house calculator: NEC-style 3W per square foot with demand factors, plus the appliances named.
| House configuration | Estimated demand | Standby class |
|---|---|---|
| Gas heat and water heater, 4.5 ton AC | 12.6 kW | 14 kW |
| All-electric (resistance heat, water heater, range, dryer) | 37.7 kW | 30 kW+ liquid-cooled |
Which tier is right at this size
At 3,500 square feet the honest math points at standby. The house's estimated demand is 12.6 kW with gas heat and hot water (a 14 kW unit) and 37.7 kW all-electric, which is past air-cooled sizes and into liquid-cooled or load-managed territory. A 4.5 ton AC alone outweighs an entire small house's essentials list.
Portables still have a role at this footprint, but it's triage, not comfort: the essentials list (2,200W running) fits a 3,500W portable, keeping food, heat circulation, and phones alive while the AC waits for the utility. What doesn't work is trying to stretch a big portable into a whole-house answer here; by the time you've bought a 12,000W unit, its transfer equipment, and the fuel to feed 60 gallons a week into it, the standby quote stopped being the expensive option.
Questions people ask
What size generator do I need for a 3,500 sq ft house?
For essentials (fridge, furnace fan, lights, electronics) a 3,500W portable covers the 2,200W load. To include the typical 4.5 ton central AC you need a 9,500W portable, and whole-house standby sizing lands at 14 kW with gas appliances or past 26 kW all-electric.
Can a portable generator run a 3,500 sq ft house?
The parts that matter, yes: the essentials list is 2,200 running watts, well inside portable range on an interlock or transfer switch. What a portable can't carry at this size is everything at once (central AC pushes the list to a 9,500W portable), so the play is picking circuits, not powering the panel like the utility does.
Does square footage even determine generator size?
Loosely. Square footage sets the lighting and plug load (3W per square foot in the NEC convention, demand-factored) and predicts the AC tonnage, but the 240V appliance list determines more: one electric water heater outweighs a thousand square feet of lights. That is why the tables here show gas and all-electric versions of the same house.