Verdict: the Mr. Heater Portable Buddy (MH9BX) is the best all-round heater for a winter power outage. Mr. Heater describes it as indoor safe, and its manual allows “emergency indoor heating when connected to a disposable 1 lb. propane cylinder,” as long as you provide a fresh-air opening and follow the other rules below. The Little Buddy (MH4B) suits one small room, the Big Buddy MH18B (Search Amazon for Mr. Heater Big Buddy MH18B ) suits a larger living area, and the Buddy FLEX (MH11BFLEX) spreads heat across 180 degrees.

“Indoor safe” is Mr. Heater’s wording, and it comes with conditions. Every manual here warns that the heater is unvented, uses oxygen from the room, and “may give off excessive CARBON MONOXIDE” without enough combustion and ventilation air. Every one says never to run it while sleeping or leave it unattended. Read the conditions before you buy, and install CO alarms before you light one.

Quick picks

Heater Best for Heat output (BTU/hr, maker) Maker’s heating area Fresh-air opening (manual)
Mr. Heater Portable Buddy MH9BX One room, most households 4,000 / 9,000 Up to 225 sq ft 9 sq in minimum (e.g., 3" x 3")
Mr. Heater Little Buddy MH4B One small room Not stated consistently Up to 95 sq ft 4 sq in at ceiling and at floor level
Mr. Heater Big Buddy MH18B (Search Amazon for Mr. Heater Big Buddy MH18B ) Larger living area 4,000 / 9,000 / 18,000 Up to 450 sq ft 18 sq in at ceiling and at floor level
Mr. Heater Buddy FLEX MH11BFLEX Wide spread in a shared room 8,000 to 11,000 Up to 275 sq ft 11 sq in at ceiling and at floor level

Output and vent areas are from each heater’s operating manual; heating areas are from Mr. Heater’s product pages, checked October 5, 2026. Mr. Heater’s product pages describe those areas with examples such as tents and cabins. Mr. Heater’s Little Buddy product page and manual don’t agree on its output, so that figure is left out. Mr. Heater’s pages and manuals give different run times, so run time is left out; check the manual for your model.

What “indoor safe” means in the manuals

Mr. Heater’s manuals for these four models share the same core conditions for emergency indoor use:

  • Disposable 1 lb cylinders only indoors. The manuals allow emergency indoor heating “when connected to a disposable 1 lb. propane cylinder.” They also say: “NEVER bring a refillable propane cylinder indoors.” Where a manual allows a hose to a refillable tank of up to 20 lb, it is for recreational or commercial enclosures with the tank located outdoors.
  • A fresh-air opening. Each manual gives a minimum vent area, listed in the table above. Mr. Heater lists an oxygen depletion sensor on all four. The Little Buddy, Big Buddy and Buddy FLEX manuals say this safety system turns the heater off if not enough fresh air is available, and not to relight until you provide fresh air.
  • Never while sleeping, never unattended. Each manual says “NEVER OPERATE THE HEATER WHILE SLEEPING!” and warns against leaving it unattended or where children could tip it over.
  • Room limits on the larger models. The Big Buddy manual allows only the “LO” setting in a bathroom and “LO” or “MED” in a bedroom. The Buddy FLEX manual says not to use it in a bathroom or bedroom at all.
  • Clearances. The manuals list 30 inches above, 24 inches in front and 6 inches at the sides (24 inches for the Buddy FLEX). The U.S. Fire Administration says to keep anything that can burn at least 3 feet from all heat sources.
  • Where you live. The manuals mark these models “for US sale except Massachusetts,” where separate Massachusetts and Canada versions are sold. The Buddy, Big Buddy and Buddy FLEX manuals add: “Not for use in a ‘dwelling home’ in California.” Mr. Heater lists a 7,000-foot maximum elevation for all four, and three of the manuals warn the heater may shut off above that height.

The Big Buddy manual spells out what Mr. Heater means by emergency use: the permanent heating system is temporarily out of service, heat is needed to prevent damage to the building or contents, the heater is not left unattended, and the minimum vent area is provided. It also says to remove the heater once the permanent heating is back in operation.

Put CO alarms in place first

The manuals warn that early signs of carbon monoxide poisoning resemble the flu, with headache, dizziness or nausea, and tell you to get fresh air at once if they appear. Because CO can’t be seen or smelled, the U.S. Fire Administration says to install CO alarms in a central location outside each sleeping area and on every level of the home. Test them before an outage, and keep spare batteries with the heater. The smoke alarm vs CO alarm guide explains which alarm covers which hazard.

Never heat the house with these

These rules come from NOAA’s National Weather Service, NFPA and the U.S. Fire Administration:

  • Ovens. The U.S. Fire Administration says never to use an oven to heat your home.
  • Grills. NFPA says gas or charcoal grills can produce carbon monoxide and should be used only outside.
  • Generators and engines. The National Weather Service says to run a portable generator outdoors at least 20 feet from doors, windows and garages. NFPA says never to run one in an attached garage, even with the door open.
  • Other fuel-burning appliances. Each Mr. Heater manual says: “Do not use other fuel burning appliances inside” while the heater runs.

The picks

Mr. Heater Portable Buddy MH9BX: best all-round outage heater

The Portable Buddy has two settings, 4,000 and 9,000 BTU per hour, and runs on one 1 lb cylinder. Mr. Heater lists a heating area of up to 225 square feet, plus an oxygen depletion sensor and an accidental tip-over shut-off. Its manual calls for a 9-square-inch fresh-air opening, such as a 3-inch by 3-inch gap.

It is the most flexible choice for one closed-off room. The low setting lets you stretch fuel, and the high setting gives more heat when the room is cold. Buy plenty of 1 lb cylinders. The manual says to store cylinders outdoors and to attach or detach them outdoors, away from flames and only when the heater is cool.

Mr. Heater Little Buddy MH4B: best for one small room

The Little Buddy is the smallest heater here, with a single heat setting and a maker heating area of up to 95 square feet. It has the same oxygen depletion sensor and tip-over shut-off as the larger models. Its manual asks for a 4-square-inch opening at the ceiling and another at floor level.

Choose it to keep one small room above freezing or to take the chill off a bedroom-sized space while you are awake. It is too small for an open-plan living area.

Mr. Heater Big Buddy MH18B: best for a larger living area

The Big Buddy (Search Amazon for Mr. Heater Big Buddy MH18B ) has three settings, 4,000, 9,000 and 18,000 BTU per hour, and holds two 1 lb cylinders. Mr. Heater lists a heating area of up to 450 square feet, an automatic low-oxygen shut-off and a tip-over shut-off.

It needs the most fresh air of the four: 18 square inches at the ceiling and again at floor level. Its manual limits it to “LO” in a bathroom and “LO” or “MED” in a bedroom, so plan to use the high setting only in a large living area. Its manual also describes running it on two 1 lb cylinders for emergency use.

Mr. Heater Buddy FLEX MH11BFLEX: best for a wide spread of heat

The Buddy FLEX has an 8,000 to 11,000 BTU-per-hour mesh burner that Mr. Heater says spreads heat across a full 180 degrees. The maker lists a heating area of up to 275 square feet and safety systems that include an emergency low-oxygen system, a tip switch and a thermal shut-down system.

It suits a living room where several people sit in an arc around the heater. Its manual calls for 11 square inches of fresh air at the ceiling and at floor level and wider 24-inch side clearances. It also says not to use it in a bathroom or bedroom.

Stay warm before you reach for a heater

The National Weather Service lists simple steps for staying warm during a power outage:

  • Wear layers of loose-fitting, lightweight, warm clothing, plus hats, mittens and blankets.
  • Close blinds or curtains to keep in some heat.
  • Close off rooms to avoid wasting heat.
  • Put towels or rags in the cracks under doors.

Gather the household into one room you can close off. A smaller space needs less heat, and that matches the room-sized heaters above. Keep the heater in that room while people are awake, and turn it off before anyone goes to sleep.

A battery power station is the wrong tool for electric heat. The apartment power station guide explains why space heaters drain a 1,000Wh-class battery quickly. Keep the station for lights, phones, a weather radio and the fridge.

How to choose an outage heater

  • Match the room, not the house. Pick the heater whose maker heating area fits the room you will close off, and remember those areas are described with tents and cabins.
  • Check your fresh-air plan. Work out where the vent opening will go before you buy. The Big Buddy needs the most air and the Little Buddy the least.
  • Count the cylinders. Indoors, all four run on 1 lb disposable cylinders. The manuals say run times can be significantly reduced when the heater runs continuously below 20°F, so store more cylinders than you expect to use, outdoors as the manuals direct.
  • Think about who is home. The manuals warn about hot surfaces and say to keep children away; the Little Buddy, Big Buddy and Buddy FLEX manuals add pets. Some people, including pregnant women and people with heart or lung disease, are more affected by carbon monoxide than others, according to the manuals.

Which outage heater to buy

Buy the Portable Buddy MH9BX for most homes, the Little Buddy for one small room, the Big Buddy for a larger living area you can ventilate well, and the Buddy FLEX for a wide spread of heat. Pair any of them with tested CO alarms, a fresh-air opening and 1 lb cylinders stored outdoors, and never use one while sleeping. For the rest of your winter outage supplies, see the 72-hour emergency kit guide and the home emergency kit checklist .

Sources checked