Costs, Runtime & Maintenance FAQs

If you haven’t sized your system yet, it can help to read the Home Generator Sizing Guide and the General Generator FAQs first. Once you have a rough kW in mind, the costs and runtime numbers below will make more sense.

How long can a standby generator run continuously?

Most residential standby generators are designed to run for extended periods during an outage, as long as:

• They have adequate fuel (natural gas supply or propane tank size).
• They’re operating within their rated load and temperature limits.
• Oil and filters are changed at the intervals specified in the manual.

In practice, many manufacturers recommend oil changes every 100–200 hours of runtime for air-cooled units. During a long outage, that might mean shutting down briefly for service every few days.

For most homeowners, the practical limit is not the machine’s absolute capability, but:

• Fuel availability (especially for propane and diesel).
• Maintenance intervals and service access.
• Local regulations on noise in residential areas.

As with any engine-driven equipment, always follow the maintenance and safety guidance in your manufacturer’s manual. For broader safety guidance on generator use and carbon monoxide, see the U.S. Consumer Product Safety Commission’s generator safety information .

How much fuel does a typical standby generator use?

Fuel use varies by size, fuel type, and load. For a common 18–24 kW air-cooled natural gas or propane standby generator, ballpark hourly usage at typical residential loads might be:

• At light load (25–50%): roughly 0.9–1.7 therms/hour of natural gas, or about 0.7–1.3 gallons/hour of propane.
• At higher load (75–100%): roughly 1.7–2.5+ therms/hour of natural gas, or around 1.3–2.1+ gallons/hour of propane.

These are approximate ranges based on manufacturer data for typical residential units. Actual consumption depends heavily on:

• The exact model and engine.
• How heavily it is loaded at any given time.
• Ambient temperature and installation conditions.

Always check the manufacturer’s spec sheets for your specific unit to get more precise fuel consumption numbers. For context on current fuel prices, you can also review data from the U.S. Energy Information Administration .

How much does it cost per day to run a standby generator?

Daily operating cost is driven by fuel price × fuel consumption. Using rough averages:

• If natural gas costs about $1.00–$1.50 per therm, and your generator uses around 1.2–2.0 therms/hour at the loads you’re running, that’s roughly $1.20–$3.00 per hour in fuel.
• If propane costs around $2.00–$3.50 per gallon, and your generator uses 1.0–1.8 gallons/hour, that’s roughly $2.00–$6.00 per hour in fuel.

Over a 24-hour period, that puts many real-world scenarios somewhere in the range of tens to low hundreds of dollars per day, depending on fuel type, usage pattern, and local energy prices.

Those numbers are intentionally broad; your actual cost may be lower or higher. For accurate estimates in your area, plug in your utility’s gas rate or your current propane price and the manufacturer’s fuel-use table for your model. A quick way to ground your assumptions is to size your system with the generator sizing calculator first, then look up fuel use for that specific kW range.

How big should my propane tank be for a whole-house generator?

It depends on how long you want to be able to run without a refill and your generator’s hourly consumption. As a very rough illustration:

• A 250-gallon tank holds less than 250 gallons of usable propane due to fill limits (often ~80% of water capacity).
• A 500-gallon tank provides significantly more runtime and is common for larger homes that rely on propane for both heating and standby power.

If your generator uses around 1–2 gallons/hour in a typical outage, a 500-gallon tank (with ~400 gallons usable) can provide on the order of 200–400 hours of runtime, spread over the outage period. In practice, you may not run 24/7, and your actual consumption may be lower, but a larger tank gives more buffer.

Your propane supplier or installer can run more precise calculations based on:

• Your generator’s fuel use at expected load.
• Whether other appliances (heat, cooking, water heating) are on the same tank.
• Local refill logistics and weather patterns.

Do I need a permit to install a standby generator?

In many jurisdictions, yes. Permits are common for:

• Electrical work (transfer switch, wiring, grounding).
• Gas work (natural gas piping or propane lines).
• Sometimes site work (slab or pad, setbacks from property lines).

Requirements vary by city, county, and state, and may involve one or more of the following departments:

• Electrical/building inspections.
• Plumbing or mechanical inspectors for fuel piping.
• Zoning or planning departments for placement & noise ordinances.

A reputable installer or electrician will typically handle permits and coordinate inspections as part of the project. If you’re managing the project yourself, it’s important to check with your local building department before work begins.

How loud are standby generators?

Most residential air-cooled standby generators list sound levels in the range of roughly 60–75 dB(A) at a specified distance (often 20–23 feet), depending on model and load. For context:

• 60 dB(A) is similar to normal conversation.
• 70–75 dB(A) is more like a vacuum cleaner a few feet away.

Actual perceived noise is affected by:

• Unit placement and orientation.
• Nearby walls, fencing, or landscaping.
• Load level (generators are often louder near full load).

Many local codes and HOA rules specify setbacks and noise limits, so placement should be planned with both comfort and compliance in mind.

What maintenance does a standby generator need?

Standby generators are engines, and they need regular service, commonly including:

• Oil and filter changes at the intervals in the manual (often every 100–200 hours or annually).
• Air filter checks/replacement.
• Spark plug inspection/replacement at recommended intervals.
• Battery inspection and periodic replacement.
• Visual checks for leaks, corrosion, and damage.
• Verification of exercise cycle (weekly or monthly self-test runs).

Many homeowners enroll in an annual maintenance program through their installer or service company, which includes oil changes and system checks. You can often do basic visual checks yourself and leave more detailed work to a professional.

How often should my generator exercise (self-test)?

Most residential standby units are set to perform an automatic exercise run once a week or once a month, typically for a short duration (for example, 5–20 minutes). The purpose is to:

• Keep the engine lubricated.
• Confirm that the unit can start and run.
• Alert you to faults before the next outage.

Frequency and duration are usually configurable within the controller’s allowed options. Your installer can recommend a setting based on your climate, fuel type, and manufacturer guidance.

How much does a whole-house generator system cost to install?

Investment varies widely based on size, fuel type, installation complexity, and local labor and permitting costs. As a general observation (not a quote):

• Many installed residential systems (including the generator, transfer switch, slab, gas work, electrical work, and permits) end up in the several-thousand to low five-figure dollar range.
• Smaller essentials-only portable setups with a manual transfer switch are usually much less expensive but require more manual operation.

To get realistic pricing for your home, it’s best to obtain quotes from a few local licensed installers. Your load profile, existing gas service, and panel location can all move the number up or down significantly.

If you haven’t sized your system yet, start with the generator sizing calculator to estimate the kW you’re likely to need. Then, use that as the basis for getting accurate quotes from installers.

← Back to all FAQ topics