Is the Mr. Heater Buddy Safe Indoors? A Power Outage Heating Guide

The house is cold, the power is out, and there is a Mr. Heater Portable Buddy in the garage or in your cart at the store. Can it come inside? The maker says it may be used for emergency indoor heating, but only under written conditions, and we can’t tell you whether your room meets them. This page lays those conditions out so you can check them against your own manual and your own house.

We did not test this heater. Everything here comes from the maker’s owner’s manual for model MH9BX (the small radiant heater that runs on a 1 lb propane cylinder) and from what the CDC and the Consumer Product Safety Commission (CPSC) say about carbon monoxide. Other Buddy models, other brands, and heaters built for big tanks have their own manuals, so if yours is not an MH9BX, read yours. If the manual that came in the box is gone, ask Mr. Heater for the copy that matches your model before you rely on this page. Follow your local emergency officials, call 911 in an emergency, and when in doubt, don’t run it.

One rule doesn’t change with the room. The manual says never to operate the heater while sleeping, so it is off before anyone goes to bed.

What the maker says about indoor use

The maker’s product page calls the Buddy an “Indoor safe radiant propane heater” in its feature list. That is marketing copy. The conditions behind it are in the manual’s General Information section:

This heater is safe for indoor use in small recreational enclosures having means for providing combustion air and ventilation, such as enclosed porches, cabins, fishing huts, trailers, tent trailers, tents, truck caps and vans. It may be used for emergency indoor heating when connected to a disposable 1 lb. propane cylinder.

Source: Enerco / Mr. Heater, Portable Buddy Heater MH9BX Operating Instructions and Owner’s Manual (the maker’s manual, model MH9BX), accessed November 2026.

That is the maker describing its own product, not a finding from an outside lab. Read closely, it is narrower than the label on the product page. The “safe” wording is tied to small recreational enclosures that have a way to bring in air. The emergency indoor heating line is tied to a disposable 1 lb cylinder. The manual does not define “emergency,” and its list does not name a living room, an apartment, or an attached garage.

The cover of the manual adds one more fact:

This is an unvented gas-fired portable heater. It uses air (oxygen) from the area in which it is used. Adequate combustion and ventilation air must be provided.

Source: Enerco / Mr. Heater, Portable Buddy Heater MH9BX Operating Instructions and Owner’s Manual (the maker’s manual, model MH9BX), accessed November 2026.

Unvented means there is no flue or pipe carrying exhaust outdoors. The heater draws its oxygen from the room, and what it gives off stays in the room. The manual warns that without adequate combustion and ventilation air, the heater “may give off excessive CARBON MONOXIDE, an odorless, poisonous gas.” That is why the rest of the manual keeps coming back to fresh air. The CDC describes how that gas builds up:

CO is found in fumes produced any time you burn fuel in cars or trucks, small engines, stoves, lanterns, grills, fireplaces, gas ranges, or furnaces. CO can build up indoors and poison people and animals who breathe it.

Source: CDC, Carbon Monoxide (CO) Poisoning Basics (cdc.gov), accessed November 2026.

What the oxygen sensor and tip-over switch do, and what they don’t

The maker points to two built-in features, and the manual describes both.

The first is an oxygen depletion sensor (ODS). The manual’s Warnings section calls it a safety system:

This heater is equipped with a SAFETY SYSTEM designed to turn off the heater if not enough fresh air is available.

Source: Enerco / Mr. Heater, Portable Buddy Heater MH9BX Operating Instructions and Owner’s Manual (the maker’s manual, model MH9BX), accessed November 2026.

The manual says not to tamper with it. If the heater shuts off, don’t relight it until you provide fresh air, and if it keeps shutting off, have it serviced.

The second is a tip-over switch. The manual says it will shut the heater off if the heater tips over, and in the same sentence says not to leave the heater unattended or where children may cause it to tip over.

Notice what the manual does not claim. It describes the sensor as designed to shut the heater off when fresh air runs short. It does not say the sensor detects or prevents carbon monoxide, and the same manual still warns about excessive CO when ventilation air is lacking. We won’t tell you either feature makes the heater safe. A carbon monoxide alarm is a separate device, and the advice to have one comes from the CDC and CPSC, covered below.

The manual’s conditions, side by side

The manual spreads its conditions across several sections. This table pulls them together as a reading aid. Every row is what the maker says, and the manual itself is still the guide for lighting, shutting down, and connecting fuel.

If you can’t meet every row, don’t run the heater in that space. For habits that apply to any portable heater, see our page on space heater safety.

On runtime, the manual gives about 3 to 6 hours on one 1 lb cylinder. It says runtimes “can be significantly reduced” when operating continuously below 20 degrees Fahrenheit, and recommends a 20 lb tank in those conditions.

A December 2004 CPSC release, “CPSC Warns Of Hazards from Heaters and Fireplaces,” adds general ventilation advice:

Keep doors open to the rest of the house if you are using an unvented fuel-burning space heater.

Source: CPSC, CPSC Warns Of Hazards from Heaters and Fireplaces (cpsc.gov), December 10, 2004 news release, accessed November 2026.

The same release says to “Follow the manufacturer’s instructions to provide sufficient combustion air to prevent carbon monoxide production.” It is an older release, so read it as background next to the manual.

Sleeping, bedrooms, and a gap the manual doesn’t explain

The manual says this in capital letters:

NEVER OPERATE THE HEATER WHILE SLEEPING!

Source: Enerco / Mr. Heater, Portable Buddy Heater MH9BX Operating Instructions and Owner’s Manual (the maker’s manual, model MH9BX), accessed November 2026.

The same manual’s specifications table lists permissible settings, with “Bathroom Use” at “LO” only and “Bedroom Use” at “HI” or “LO.” Its safety instructions also cap the input setting for emergency home use in a bathroom and in a bedroom.

Side by side, those lines raise a question. The manual gives a bedroom setting and also says never to run the heater while sleeping. It doesn’t explain how the two fit together, and we won’t guess. Both the manual and the CPSC draw a firm line around sleep. The CPSC says:

Never operate unvented fuel-burning appliances in any room where people are sleeping.

Source: CPSC, Carbon Monoxide Questions and Answers (cpsc.gov), accessed November 2026.

The CDC explains why sleep is the dangerous time:

People who are sleeping, drunk, or under the influence of other substances can die from CO poisoning before they have symptoms.

Source: CDC, Carbon Monoxide (CO) Poisoning Basics (cdc.gov), accessed November 2026.

Turn the heater off before anyone goes to sleep. For getting through a cold night without anything burning in the room, see what to do during a power outage at night.

Where the heater is restricted

The manual’s cover says it is for US sale except Massachusetts, and a notice inside says it is not for use in a “dwelling home” in California. The maker’s FAQ page says the heater is restricted from all indoor use in Massachusetts and Canada, and from use in dwellings in California. Those are the maker’s statements, and we have not checked them against the law.

Beyond those, we don’t know. Other states, cities, building codes, and apartment leases may have their own rules on unvented fuel-burning heaters. Call your local fire department before using one indoors and ask what applies where you live.

Carbon monoxide alarms and warning signs

The manual warns that early signs of carbon monoxide poisoning “resemble the flu, with headache, dizziness, and/or nausea,” and that if you have them, the heater may not be working properly, so get fresh air at once. The CDC lists the most common symptoms as “headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion,” and describes the gas this way:

Carbon monoxide (CO) is an odorless, colorless gas that kills without warning.

Source: CDC, Carbon Monoxide (CO) Poisoning Basics (cdc.gov), accessed November 2026.

The manual describes the heater’s sensor as responding to a lack of fresh air, not as a carbon monoxide alarm, and we didn’t find an instruction to install an alarm in the manual text. That advice comes from the agencies. The CPSC says:

Install battery-operated CO alarms or CO alarms with battery backup on every level of the home and outside sleeping areas.

Source: CPSC, Carbon Monoxide Questions and Answers (cpsc.gov), accessed November 2026.

The CDC says to put battery-operated or battery back-up detectors near every sleeping area. In an outage, the battery part matters. The CPSC also says an alarm “can provide some added protection, but it is no substitute for proper use and upkeep of appliances.”

If you need one, our roundup of the best carbon monoxide detectors is a place to start. Our guide to carbon monoxide detector placement covers where it goes, and our binder resources page lists a smoke and carbon monoxide alarm among its fire safety items.

If the alarm sounds, the CPSC says not to try to find the source of the CO:

Immediately move outside to fresh air.

Source: CPSC, Carbon Monoxide Questions and Answers (cpsc.gov), accessed November 2026.

Then call your emergency services, fire department, or 911. Our page on what to do when a carbon monoxide alarm is beeping goes through the rest.

Questions people ask

Can I run it in the garage?

The manual doesn’t address running the heater in a garage. It does say cylinders must not be stored in a building, garage, or any other enclosed area. Ask the maker and your local fire department before running it in an attached garage.

What about an apartment or a living room?

The manual lists small recreational enclosures such as porches, cabins, trailers, and tents, and separately says the heater may be used for emergency indoor heating with a disposable 1 lb cylinder. It doesn’t say whether an apartment or a family living room counts, or how you would make the vent openings work there. Ask the maker and your local fire officials, and check your lease.

Can I use it in a tent?

Tents and tent trailers are on the manual’s list of small recreational enclosures, and its window or roof vent warning applies to any recreational enclosure. The sleeping rule applies in a tent the same as in a house.

Can I use a 20 lb tank indoors?

The manual says never to bring a refillable propane cylinder indoors. A remote 20 lb tank may be used only when it stays outside and the heater is connected with one of the hoses the manual names.

If you can’t meet the conditions

Then don’t run it indoors. There are ways to stay warm that don’t burn fuel in the room, from layers to a wool blanket, and we cover them in how to stay warm without power. For getting the house ready before cold weather arrives, see how to prepare for a winter storm.

The Family Emergency Binder has a Power Outage page with the first steps and the carbon monoxide rules for generators, so the plan is written down before the next cold night.