Guide 73 · Generator
Can a Portable Generator Run a Tankless Gas Water Heater?
Usually, yes. A tankless gas water heater burns gas for heat but needs electricity for its controls, igniter, and fan, so a small inverter generator can often cover it. The harder questions are how the heater is wired and whether it accepts your generator's power.
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The verdict
Buy an inverter generator whose running watts clear your heater's rated electrical draw plus anything else you plan to run, and confirm with a licensed electrician how the heater will be connected before you buy.
See the store linkWhat we check
- Running watts above the heater's label rating
- Inverter output for sensitive electronic controls
- Neutral and grounding setup the heater accepts
- Safe connection through a transfer switch or interlock
- Runtime at your actual load
- Voltage that matches the heater's rating
Drawing of backup power equipment.
Store link Generator
Honda EU2200i 2200 Watt Inverter Generator (EU2200ITAN) | Super Quiet 120V Gas Powered Portable Generator for Camping or Home Backup Power Supply, Up to 8.1 Hour Run Time
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The unit named above, on Amazon.
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Generator safety: carbon monoxide and backfeed
Carbon monoxide: never run a generator indoors, in a garage, basement or crawlspace, or near windows, doors or vents. Using a generator indoors can kill you in minutes. Use battery-powered carbon monoxide alarms in the home. CPSC Safety Alert 5123
Backfeed: never plug a generator into a wall outlet or a dryer outlet. That is extremely dangerous: it can energize utility lines and injure line workers and people in the home. Use a transfer switch or interlock installed by a licensed electrician. CPSC Safety Alert 5123 (PDF)
Why a gas heater still needs electricity
A tankless gas water heater lights its burner only when you open a hot tap. To do that, it needs power for the circuit board, the electronic igniter, and the fan that pushes exhaust out the vent. When the grid goes down, most units stop heating even though the gas is still on.
Some units also have built-in freeze protection heaters or a recirculation pump. Those can add to the electrical load, especially in cold weather. Your installation manual tells you which features your unit has and how they are powered.
Find your heater's actual power draw
Do not guess. Look at the rating label on the heater, usually inside the front cover or on the side, and the electrical section of the installation manual. If the heater plugs into a wall outlet, a plug-in watt meter can show you what it draws while firing.
Add your other loads to that number. For example, if your heater's label lists 150 watts and you also want to run a refrigerator labeled 700 watts and some lights totaling 100 watts, you need a generator with more than 950 running watts, plus headroom for any appliance that surges at startup.
Leave a margin. Running a generator near its limit makes voltage less steady, and electronic controls are the first thing to complain.
- Heater rating label or installation manual
- Labels or power bricks on every other device you plan to run
- A plug-in watt meter for anything with a standard plug
- The maker's spec page for startup or surge needs
Why an inverter generator suits this job
A tankless heater's circuit board is sensitive electronics. An inverter generator produces steadier output than many conventional open-frame models, which is why inverter units are a common choice for this load. Rinnai's New Zealand guidance, for example, says its units need a full sine wave, so check your heater's manual for its power requirements.
Grounding is the other thing to check. Look in the generator manual for how its neutral is configured, and ask the heater maker's support line whether their unit has any generator requirements. Your electrician can tell you the safe way to handle it for your setup.
Connecting the heater safely
How you connect depends on how the heater is wired. If it has a cord and plug, check its manual for any notes about generator power, then use an outdoor-rated extension cord sized for the load.
Many tankless heaters are hardwired. Never backfeed a house circuit by plugging a generator into a wall outlet. Connecting a generator to house wiring takes a transfer switch or interlock installed by a licensed electrician. Inlets and transfer switches take specific plug types, so ask your electrician to check the generator's outlet type and confirm what is safe before you buy cords or adapters.
Where the Honda EU2200i fits
The listing on this page is the Honda EU2200i. Its title lists 2200 watts, 120V output, inverter design, and up to 8.1 hours of run time. That suits a heater rated for 120V with room left for a few other essentials, as long as your added-up running watts stay comfortably under its rating.
Run time depends on load, so check the maker's runtime chart at your own wattage rather than counting on the top figure. If your list grows to include a well pump, central air, or 240V loads, you will need a larger generator, and a home standby unit may serve you better.
Generator safety basics
Never run a generator indoors, in a garage, in a basement, or near windows, doors, or vents. Generator exhaust contains carbon monoxide, which you cannot see or smell. Place it outside, well away from the house, with the exhaust pointed away from openings.
Install battery-powered carbon monoxide alarms inside the home. Let the generator cool before refueling, and store fuel away from living spaces.
Sources
Recorded AI check: Oct 5, 2026. The sources below may include later additions. AI checks compare factual numbers and checkable claims with web sources; they do not verify every statement.
- Honda generator brochure (PDF)
- Rinnai residential tankless water heater FAQ
- Rinnai NZ: INFINITY running on off-grid electrical power (PDF)
- CPSC Safety Alert: Portable Generator Hazards (PDF)
- OSHA fact sheet: Using Portable Generators Safely (PDF)
Best inverter generator for a home outage compares units from the makers' numbers. Every guide in this class is in Portable generators.
How this guide was made
- Drafted and checked with AI. An AI model wrote the draft from the guide's topic. A second AI pass looked for factual numbers to check against web sources. This does not verify every statement. A draft that fails the check is held for review.
- Fact-checked by the HoldBackup editorial team. On , a person on the HoldBackup editorial team reviewed this guide against its sources. That is a review of the writing, not a test of any unit.
- General guidance only. No prices, rankings, or test results, because we have none to back them. Check any number against the maker's own spec sheet.
- No lab tests, and we say so. HoldBackup has not run any unit named here.
- The store link is not a pick for this guide. It goes to a unit in this product class that this guide does not review. Check it against the list above before you buy.
- Labelled store links. A store button goes straight to Amazon with HoldBackup's affiliate tag. HoldBackup counts the click. A live button carries a "paid link" label, and the disclosure sits above the first one on every guide.
Questions
Will a tankless gas water heater work during an outage with no power at all?
Most will not. They need electricity for the controls, igniter, and fan even though gas provides the heat. Check your installation manual to see what your unit requires.
Why does my tankless heater show an error code on generator power?
Possible causes include unsteady or clipped power from the generator, not enough running watts, or how the generator's neutral is set up. Look up the code in the heater manual, check the generator manual for its neutral setup, and call the heater maker's support line.
Can I plug a hardwired water heater into a generator?
Not directly. A hardwired heater has to be fed through a transfer switch or interlock installed by a licensed electrician. Never plug a generator into a wall outlet to backfeed the house.
How big a generator do I need for the heater plus other appliances?
Add up the running watts from the heater's label and every other device's label or spec page, then allow headroom for startup surges. Pick a generator whose running watts exceed that total with a margin to spare.
Where does the price button go?
Straight to Amazon. Amazon sets the price and availability, and both can change.
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