Best Indoor-Safe Heaters for Power Outages (and How to Use Them Safely)

Winter storms are among the outages that matter most, because losing heat is a health risk, not just an inconvenience. NERC's 2025–2026 Winter Reliability Assessment found all areas had adequate resources for normal winter peaks but warned that more extreme winter conditions over a wide area could cause electricity supply shortfalls.

This guide covers heaters that their manufacturer rates for indoor use, and the safety rules that must come with them. It is research-based: picks come from manufacturer specs and official safety guidance; we do not test products. Read the safety section before buying anything that burns fuel.

Carbon monoxide first: the non-negotiables

Carbon monoxide is odorless and colorless. During outages, CO poisoning is driven by people bringing outdoor equipment inside to stay warm or keep the lights on. CPSC's January 2026 winter release reports about 750 deaths from generator-related CO poisoning between 2012 and 2022. If you run a generator, CDC and CPSC say to keep it outside, at least 20 feet from the home, with exhaust pointed away from windows, doors and vents.

A CO alarm with battery power or battery backup is mandatory if you use any fuel-burning heater indoors. Check alarm batteries twice a year; CDC suggests doing it when clocks change in spring and fall.

What makes a heater "indoor-safe"

Only use a fuel-burning heater indoors if its manufacturer explicitly rates it for indoor use. The heaters below are all listed as "Indoor-safe: Yes" on Mr. Heater's spec tables and include an Oxygen Depletion Sensor (ODS), which shuts the heater off if oxygen in the room falls, and a tip-over switch that shuts it off if it is knocked over.

Two important limits from the same spec tables: the ODS is rated up to 7,000 ft of elevation, and Mr. Heater lists state restrictions for Massachusetts and country restrictions for Canada, where these models are not sold for that use.

Patio heaters, construction "torpedo" heaters, camp stoves and grills are outdoor equipment. Never bring them inside.

Ventilation and placement

Indoor-rated is not the same as sealed-room safe. CPSC notes that unvented heaters "require a constant supply of fresh air to operate safely and to avert the buildup of poisonous gases." Follow the ventilation instructions in your heater's owner's manual exactly; they specify how much fresh-air opening is required for the size of room.

• Keep heaters at least three feet from drapes, furniture, bedding and other combustible materials (CPSC).
• Never refuel a fuel-burning heater while it is running; turn it off and let it cool first (CPSC).
• Place the heater on a flat, hard surface where kids and pets cannot knock it over.
• Follow your owner's manual on unattended operation and bedroom use; when in doubt, turn the heater off before sleeping and use blankets and sleeping bags.
• Store spare propane cylinders outdoors, never in a living space.

Heat less space for longer

A small heater cannot keep a whole house warm, and every cylinder has a limited runtime. Pick one room, ideally an interior room with few windows, close the doors to unused rooms, cover windows with blankets or curtains at night, and dress in layers. Sizing matters: compare the heated-area rating to the room you will actually use, and plan fuel from the manufacturer's runtime per cylinder.

Fuel math example using Mr. Heater's spec table: the Portable Buddy runs about 3 hours on high or 6 hours on low per 1 lb cylinder. Heating one room for 6 hours a day on low for 3 days is about 3 cylinders; on high, about 6. Longer outages are where the 20 lb tank option (with the correct hose and filter) makes sense.

Research-based picks: manufacturer-rated indoor-safe heaters

All four are propane radiant heaters that Mr. Heater rates as indoor-safe with ODS and tip-over shutoff. Specs are from mrheater.com product pages, checked October 27, 2026.

No. 1Indoor-safe heater

Mr. Heater Portable Buddy MH9BX

Best for: Keeping one room warm during a winter outage

• 4,000–9,000 BTU, heats up to 225 sq ft
• Oxygen depletion sensor (ODS) and tip-over auto shutoff
• Runs on a 1 lb propane cylinder
• Marketed by the maker as indoor-safe heat

Tradeoffs

• · Still burns propane: crack a window for ventilation, keep a CO alarm in the same room, and expect 1 lb cylinders to empty quickly.
• · Only about 3 hours per 1 lb cylinder on high, so long outages need many cylinders or the 20 lb setup
• · 20 lb hose and filter are extra purchases

Check price on AmazonRead the full reviewSpecs: manufacturer page, checked Nov 1, 2026

No. 2Indoor-safe heater

Mr. Heater Big Buddy (MH18B)

Best for: Larger rooms up to 450 sq ft

• 4,000 / 9,000 / 18,000 BTU/hr; heats up to 450 sq ft
• Takes two 1 lb cylinders, or a 20 lb tank with optional hose (sold separately)
• Manufacturer: up to 11 hours with dual 1 lb tanks
• ODS, tip-over shut-off; 17.1 lb
• Manufacturer spec table: "Indoor-safe: Yes", Oxygen Depletion Sensor (ODS), tip-over switch, max elevation 7,000 ft

Tradeoffs

• · Heaviest and largest of these picks
• · Mr. Heater notes the fan has been removed on some MH18B units due to tariff changes; check the listing

Check price on AmazonRead the full reviewSpecs: manufacturer page, checked Nov 1, 2026

No. 3Indoor-safe heater

Mr. Heater Little Buddy (MH4B)

Best for: A small room or bathroom up to 95 sq ft

• 3,800 BTU/hr, single setting; heats up to 95 sq ft
• Connects directly to one 1 lb disposable cylinder
• Runtime: 5.6 hrs per cylinder
• ODS, tip-over shut-off; 5.85 lb
• Manufacturer spec table: "Indoor-safe: Yes", Oxygen Depletion Sensor (ODS), tip-over switch, max elevation 7,000 ft

Tradeoffs

• · Single heat level and small coverage
• · No 20 lb tank option listed by the manufacturer

Check price on AmazonRead the full reviewSpecs: manufacturer page, checked Nov 1, 2026

No. 4Indoor-safe heater

Mr. Heater Buddy FLEX Heater (MH11BFLEX)

Best for: Mid-size rooms up to 275 sq ft

• Up to 11,000 BTU/hr; heats up to 275 sq ft
• 1 lb cylinder; runtime 2 hrs on max, 3.5 hrs on min
• Low-oxygen safety system, 50° tip-switch and thermal shut-down
• Electronic ignition (battery compartment)
• Manufacturer: indoor-safe "YES (Excluding Canada and Massachusetts)"

Tradeoffs

• · Shortest runtime per cylinder of these picks
• · Ignition depends on batteries

Check price on AmazonRead the full reviewSpecs: manufacturer page, checked Nov 1, 2026

Heat-loss checklist before you light anything

• Battery or battery-backup CO alarm on every level and near sleeping areas, tested
• Owner's manual read, with its ventilation and room-size rules followed
• One room chosen; doors to unused rooms closed
• Three-foot clear zone around the heater
• Spare cylinders stored outside
• Warm layers, hats, sleeping bags and blankets for everyone

Electric heat needs a lot of backup power

Electric space heaters draw far more power than lights, phones or a fridge, so running one from a battery drains it quickly. CPSC also says to plug electric space heaters directly into a wall outlet, never an extension cord or power strip. If you want electric heat during outages, size the backup power first with the backup power calculator.