A home standby generator is best sized around the appliances and systems you need during an outage, not every circuit in the house. Start by identifying essential loads, then account for both their normal running demand and the extra power some motors need when starting. Fuel supply, transfer equipment and installation conditions also affect which generator will work for your home. A focused load plan can keep refrigeration, selected lighting, heating controls, a water pump or other priorities available without paying for capacity you’re unlikely to use. The right size depends on your equipment and how you intend to use it, so treat a load assessment as the starting point for a professional design.
Before comparing generator ratings, write down what an outage would make difficult or unsafe in your household. Priorities vary: one home may need a well pump and heating system, while another may put medical equipment, refrigeration and communications first. Include equipment that supports an essential system, such as a heating unit’s controls or circulation pump, not only the main appliance.
It helps to sort loads into three groups. The first contains equipment that must stay on or be restored quickly. The second contains useful loads that can run when capacity allows. The third includes high-demand conveniences you can leave off during an outage, such as an oven, clothes dryer or workshop equipment. These are planning categories, not fixed rules; a particular appliance can move into a higher priority if your household depends on it.
| Load group | Possible examples | Planning decision |
|---|---|---|
| Essential | Medical equipment, refrigeration, selected lights, a water pump, heating controls | Decide whether each needs continuous power, or can tolerate a brief interruption. |
| Useful | Internet equipment, additional lighting, a home office, selected kitchen outlets | Include only if there is enough capacity after essential loads are covered. |
| Optional or high demand | Oven, clothes dryer, electric water heating, workshop tools, some heating or cooling loads | Leave out, use one at a time, or add through a suitable load-management plan. |
Give special attention to medical devices and temperature-sensitive needs. Ask the equipment supplier or care provider what power quality and continuity the device requires, and whether its own battery backup is adequate for the outages you plan for. A generator with an automatic transfer switch still takes time to start and transfer power, so it is not a substitute for an uninterruptible power supply where even a short interruption is unacceptable.
Generator sizing is not simply a matter of adding the wattage printed on every appliance. The calculation needs to account for which devices will operate together, their normal demand and any higher starting demand. Compressors, pumps and other motor-driven equipment may briefly draw more power as they start. If several such loads start at once, a generator that appears adequate from running figures alone may struggle.
Don’t size from the main breaker rating or the sum of every circuit’s breaker rating. Those figures describe parts of the electrical installation; they don’t show what the household will draw during an outage. Equally, don’t select a generator by adding only the appliances’ normal running watts and ignoring startup needs.
Leave room for a realistic change in use, such as adding a necessary appliance, but avoid buying capacity for hypothetical loads without a reason. Larger capacity can affect equipment and installation choices, while an undersized unit can limit which loads operate together. Ask the installer to show the assumptions behind the proposed size, including which loads are included, which are excluded and how starting demand is handled.
A home standby generator does not have to supply every circuit. A dedicated essential-load arrangement can keep the design focused, while load management may allow additional appliances to be connected without treating all of them as simultaneous demands. Whole-home coverage can be appropriate for households with broad backup needs, but it doesn’t automatically mean every large appliance can run at the same time.
| Setup | Suitable when | Main advantage | Limitation to consider |
|---|---|---|---|
| Essential circuits | You have a short, well-defined list of priority loads. | Capacity is directed toward the systems you need most. | Circuits left outside the backup arrangement won’t be available from the generator. |
| Essential circuits with load management | You want some additional loads, but can accept controls that limit what runs together. | Selected loads can be prioritised or managed as demand changes. | The installer must confirm the controls suit the equipment and your intended use. |
| Broad or whole-home coverage | You want more circuits available and have loads that justify the added capacity. | There may be less need to decide which individual circuits to include. | High-demand appliances still need to be considered together; the design and fuel supply must support the plan. |
Load management is useful when a few large appliances are unlikely to be needed at once. It can control which loads are enabled based on the system design, but it doesn’t increase the generator’s physical output. Ask which appliances may be delayed or temporarily switched off, how the system handles competing demands, and whether you can operate it as expected during an outage.
Fuel availability can matter as much as the generator’s rated output. A unit that suits the load calculation may not be a practical choice if its fuel is difficult to supply or store at the property. Confirm which fuels the specific model supports: not every standby generator can use every fuel type.
| Fuel option | Potential benefit | What to check |
|---|---|---|
| Natural gas | A connected supply can avoid keeping a separate fuel store on site. | Confirm the service and fuel arrangement can support the generator at the required demand, and consider what happens if gas service is interrupted. |
| Liquefied petroleum gas (LPG) | Fuel can be stored on the property where a suitable supply is available. | Check tank capacity, placement, delivery access and how fuel consumption affects the runtime you need. |
| Diesel | May suit a property or system already planned around diesel equipment. | Confirm the specific generator is intended for standby use, and plan for safe storage, fuel condition and servicing. |
For any fuel, ask the installer how the generator’s output changes, if at all, between supported fuel types, and whether the proposed supply arrangement meets the equipment requirements. A fuel source that appears convenient still needs to be available during the kind of outage you are preparing for. For stored fuel, consider how you’ll monitor supply and arrange replenishment if an outage lasts longer than expected.
A permanently installed home standby generator needs a properly designed connection to the home’s electrical system. An automatic transfer switch can detect a loss of utility power, start the generator and transfer selected circuits to generator supply. When utility power returns, the system can transfer back according to its controls. The switch and generator must be sized and configured for the intended loads.
Transfer equipment also separates the generator supply from the utility supply. This matters for safety: a generator must not feed electricity back into the network. Never connect a standby generator to a household circuit through an improvised connection or an ordinary wall outlet. Have a qualified electrical professional design and install the transfer arrangement, and confirm any local approval or inspection requirements that apply.
Location is another design issue. The generator must be installed outdoors in a position that follows the manufacturer’s requirements for exhaust, ventilation, access and distance from openings or occupied areas. Exhaust contains carbon monoxide; never operate a generator indoors, in a garage or in another enclosed space. The installer should also consider noise, weather exposure, service access and the route for electrical and fuel connections.
For a New Zealand home, confirm that the generator’s voltage, frequency and phase are compatible with the property and the appliances it will supply. This is especially worth checking when considering equipment sourced from another market. Ask for an explanation of how the transfer switch, fuel connection and selected circuits will work as one system, rather than judging the generator as a standalone purchase.
The generator itself is only one part of the project. The total installed scope can include transfer equipment, electrical work, fuel-system work, a suitable mounting base, required controls, commissioning and any site-specific preparation. A larger generator may change more than the equipment line on a quote, so compare proposals based on the same load plan and installation assumptions.
Ask each installer to itemise what is included and to state what could require additional work. Check whether the quote covers the circuits you listed, the fuel supply, testing of the transfer system, handover instructions and ongoing servicing. If one proposal is cheaper because it excludes a necessary part of the installation, it is not a like-for-like comparison.
Useful questions before accepting a design include:
A standby generator needs maintenance even if it rarely runs during an outage. Follow the manufacturer’s schedule for servicing, battery checks, exercise cycles and other inspections; requirements vary by model and operating conditions. Keep the manual and service records where someone in the household can find them.
During commissioning, ask the installer to demonstrate the normal transfer process, explain any status indicators or alarms, and show how to manage the backed-up loads. Make sure household members know which appliances to switch off if demand is too high. If you rely on medical equipment or another critical load, include its backup plan in your outage preparations rather than assuming the generator alone will cover every interruption.
It can be designed to supply a broad set of circuits, but the generator must be sized for the loads you expect to use together. Large appliances may need to be excluded or controlled so their combined demand and starting requirements stay within the system’s capacity. Ask for a load calculation rather than assuming “whole home” means every appliance can run simultaneously.
A generator may be undersized if the planned simultaneous loads exceed its usable output, particularly when motor-starting demand is included. The design should identify which appliances can run together and how the system handles their startup. Have an electrician review the appliance information and proposed load schedule before purchase.
No. An automatic transfer system can respond to a power loss, but the generator needs time to start and the transfer equipment needs to change the supply. Use a suitable battery backup or UPS for equipment that cannot tolerate even a short interruption, and confirm its requirements with the device provider.
Include it if maintaining indoor temperature is a priority, but assess the full system rather than looking only at the thermostat. Heating or cooling equipment may rely on motors, pumps or controls with their own electrical requirements. The installer should check its running and starting demand and explain what else can operate at the same time.
No. More capacity can support a broader load plan, but it may add cost and installation requirements without helping if your essential needs are modest. Choose capacity from a documented assessment of required loads, startup demand and fuel supply, then allow for only the future needs you can reasonably anticipate.
For a well-sized home standby generator, define the essential loads first, decide which other appliances can be managed, and have a qualified installer calculate the required capacity. Compare complete installation proposals that use the same load assumptions, fuel plan and transfer arrangement. That approach helps you cover the systems that matter without buying capacity your outage plan doesn’t need.
