How to Size a Standby Generator for a New Hampshire Home
Every standby generator installation in New Hampshire is unique. The right size depends on your home's actual electrical loads, your priorities during an outage, the available fuel source, and local code requirements. Bigger is not automatically better. An oversized generator costs more to buy, more to operate (a 25 kW unit can burn through 5 gallons of propane per hour at full load), and more to maintain than a properly sized one.
At A.J. LeBlanc Heating, we size generators around what each homeowner actually needs to run during an outage. Power management modules are part of why we can install smaller, more efficient units that still cover almost everything you care about. Here is how that works.
The case against oversized generators
Some electrical contractors quote standby generators sized to the home's total electrical service (often 200 amps, or roughly 48 kW). The logic sounds reasonable: "What if everything is running at once?" In practice:
- Almost no home actually runs everything at once, even during normal operation.
- Outages are temporary scenarios where people are usually being more conservative with power use, not less.
- A 25 kW unit can burn around 3.5 gallons of propane per hour at full load. At $3.75 per gallon (NH average as of mid-2026), that is about $13 per hour, over $300 per day.
- Standby generators also run a self-test every week (typically 5 to 12 minutes), so an oversized unit costs more to maintain even during normal weeks.
- Larger generators require larger transfer switches and heavier-gauge wiring, all of which add upfront cost.
How power management changes the calculation
A power management module (PMM) is a small device installed at the transfer switch that monitors generator load in real time. If a large appliance starts up and would push the generator past its capacity, the PMM temporarily disconnects ("sheds") a designated lower-priority load. When the heavy load finishes its cycle, the PMM restores the dropped load automatically.
Typical large loads that are managed:
- Electric water heater
- Electric range or oven
- Electric clothes dryer
- Central AC compressor
- Hot tub heater
- EV charger
By managing these loads intelligently, a smaller generator can serve a home that would otherwise require a much larger unit.
Typical generator sizing for NH homes
For a typical southern NH single-family home:
- 11 kW to 14 kW with power management: covers essential loads and most regular appliances. Cannot run the electric range and the dryer at the same time as the AC, but the PMM handles that automatically.
- 18 kW to 20 kW: covers essentially everything in a typical home, including central AC during normal operation.
- 22 kW to 26 kW: larger homes or homes with multiple AC zones, electric range, electric water heater, and EV charging.
- 30 kW+: very large homes or homes with significant electric demand (whole-home heat pumps, electric heat, multiple EV chargers).
Most NH families end up well-served by a properly sized 11 to 18 kW unit paired with a power management module.
What sizing the right way includes
A proper generator sizing conversation covers:
- What you absolutely must run during an outage (heat, well pump, refrigerator, sump pump)
- What you would like to run but can live without (AC, dishwasher, dryer)
- Existing electrical service size
- Available fuel source (natural gas vs. propane, and tank size if propane)
- Expected runtime for the typical outage in your area
- How long you can wait before refueling becomes an issue (propane tank capacity)
- Future loads you might add (EV charger, heat pump)
Fuel runtime planning for propane
For homes on propane, runtime under load matters because the tank only holds so much fuel:
- An 11 kW generator under typical home load burns roughly 1 to 2 gallons per hour
- A 500-gallon propane tank typically holds 400 usable gallons (80 percent fill)
- At an average draw of 1.5 gph, that is roughly 10 to 11 days of continuous runtime
- A 22 kW generator under similar load uses 2.5 to 4 gph, which is roughly 4 to 6 days
Sizing the generator smaller, with power management, extends runtime substantially on the same tank.
Schedule a generator sizing consultation
If your New Hampshire home loses power often enough to think about a generator, or you have an undersized or aging unit you want to upgrade, contact A.J. LeBlanc Heating. We size every install around what your home actually needs. Serving NH families since 1928.
Frequently Asked Questions
What size generator do I need for my home?
For most NH homes, 11 kW to 18 kW with power management is sufficient. Larger homes or homes with significant electric loads (EV charging, whole-home heat pumps, electric range) may need 22 kW or larger. A sizing consultation with a licensed installer is the only way to know for sure.
What does a power management module do?
It monitors generator load in real time and temporarily disconnects designated large appliances when their combined demand would overload the generator. When the heavy load finishes, the PMM automatically reconnects it. This lets a smaller generator serve a larger home.
Can I run my whole house on an 11 kW generator?
Yes, with a power management module, for most NH homes. You may not be able to run every large appliance simultaneously, but everything essential plus most regular use is covered.
How much fuel does a generator use?
It varies with load. An 11 kW propane generator at typical home draw uses 1 to 2 gallons per hour. A 22 kW unit at similar load uses 2.5 to 4 gallons per hour. Larger generators burn more fuel even when they are not under full load.
How often does a standby generator run a self-test?
Most units run a brief self-test weekly, typically 5 to 12 minutes at a programmed time of day. This confirms the engine, battery, and transfer switch are working.