Mr. Heater Portable Buddy Review: The Right-Size Propane Heater

The Mr. Heater Portable Buddy (MH9BX) is the propane heater we'd hand most people: one person or three in an ice shack, a canvas tent, a truck cap or a van, or one room during a power outage. It makes 4,000 or 9,000 BTU/hr on a single 1 lb cylinder, shuts itself off on low oxygen or if it tips, and carries an indoor-use statement in its US manual. For the jobs it was built for, that's enough heat, and it costs a good deal less than the Big Buddy.

It is still an unvented flame in a small space. The manual's indoor permission comes with conditions, a 9 sq in opening at the ceiling and another at floor level, never while you sleep, 1 lb cylinders only for emergency heat at home, and the low-oxygen shutoff does nothing about carbon monoxide. Buy a CO alarm with it. Expect condensation, a pilot that hates wind, and heat that rises to the ceiling because there's no fan.

What it does well

• The right amount of heat: 4,000 BTU/hr on LO and 9,000 on HI, rated for up to 225 sq ft. Most small shelters and tents run it on LO.
• Simple fuel: it screws onto one 1 lb cylinder, and a swivel regulator takes a Mr. Heater hose and filter for a remote tank kept outdoors.
• Indoor-rated, with limits: the US manual allows recreational enclosures with a window or roof vent, and emergency home heating on a 1 lb cylinder.
• Two shutoffs: a low-oxygen pilot (ODS) and a tip-over switch.
• Allowed in a bedroom on HI: for emergency home use while you are awake, its 9,000 BTU/hr fits under the 10,000 BTU/hr bedroom limit in its manual, which the Big Buddy's HI does not.

What to watch for

• No thermostat, no fan: you control it by switching between LO, HI and off, and the heat climbs to the ceiling.
• Moisture: unvented combustion puts water vapor into the space; vans and tents drip.
• Touchy pilot: wind outdoors and stale air indoors both shut it off, by design in the second case.
• Short cylinder life: about 3 hours on HI and 6 on LO per 1 lb cylinder, per the manual.
• Warranty confusion: the manual says 3 years; Mr. Heater's warranty-policy page and the Amazon listing say 1 year.

How much space 9,000 BTU covers

Mr. Heater's 225 sq ft claim works out to 40 BTU/hr per square foot on HI, the same ratio the Big Buddy uses for its 450 sq ft. In a shelter, wind and insulation matter more than floor area. One ice angler worked out a heat need of about 1,548 BTU/hr for an insulated three-person hub at a 70-degree difference, using a rule of thumb for single-wall tents. The Portable Buddy's LO setting is about 2.6 times that, which is why owners of two- and three-person shacks mostly run it on LO.

Where it falls short: big hubs, long nights well below zero in wind, and drafty rooms in a house. That's the Big Buddy's territory. Its manual also gives a minimum ambient temperature of 0°F, and below 20°F cylinder run time can drop sharply, which owners notice as a heater that fades as the bottle frosts over.

Indoor use, by the manual

The US manual (32178 REV F) says the heater is safe for indoor use in small recreational enclosures with means for combustion air and ventilation, such as enclosed porches, cabins, fishing huts, trailers, tent trailers, tents, truck caps and vans, and for emergency indoor heating on a disposable 1 lb cylinder. Those permissions come with conditions:

• Venting: at least 9 sq in (a 3 x 3 in opening, for example) at the ceiling and at floor level while it runs. One cracked window at one height doesn't meet that.
• Enclosures: only with a window or roof vent; without one, the manual says do not use it inside.
• Home emergencies: 1 lb cylinders only, LO only in a bathroom, HI or LO in a bedroom, no other fuel-burning appliances running inside, and never left unattended.
• Sleep: never operate it while sleeping. The CPSC also says to shut off any camping heater before going to sleep.
• Tanks: a refillable cylinder never comes indoors. A remote tank up to 20 lb is for recreational enclosures, kept outdoors, on a Mr. Heater hose.
• Vehicles: not in a moving vehicle.
• Where it's not for: not for use in a dwelling home in California, per the manual, and Mr. Heater's page lists Massachusetts and Canada sale restrictions. A Canada version is sold separately; we haven't read its manual, so read the one in your box.

Owners bend these rules, and you'll find stories of people sleeping with one running or bringing a 20 lb tank indoors. We'd follow the manual. A garage isn't on its indoor list either, and the manual says that with a cylinder attached, the heater must be stored outdoors and not in a building or garage.

CO, moisture and the missing fan

Buy a battery CO alarm listed to UL 2034 and run it whenever the heater does. The ODS watches oxygen and shuts the gas when it runs short; it does not measure carbon monoxide, and the CPSC says an alarm adds protection without replacing proper use. Keep the alarm off the spot directly above the heater. The manual lists the early signs of CO poisoning as flu-like headache, dizziness and nausea: get fresh air at once and have the heater serviced.

Moisture is the price of unvented heat. A van or a small tent will collect condensation on cold walls and windows, and the venting the manual asks for is also what carries the water out. If dampness is a constant fight in a van you live in, a vented heater is the better long-term answer.

There's no fan, and heat pools at the ceiling. A small battery fan placed nearby, not attached to the heater, moves it around; one owner swears by a USB rechargeable one with a light. Don't clip anything onto the heater or set a stove fan on top. The manual calls hand-made or third-party accessories extremely dangerous, and they void the warranty.

Mind the clearances in tight spaces: 30 in above, 24 in in front, 6 in at the sides and 0 in behind. In a truck cap that's hard to find. One owner found that the heater toasted the felt liner near the cab and overheated the rear glass at the other end.

Fuel, hoses and the filter

On 1 lb cylinders the manual gives about 3 hours on HI and 6 on LO. A 12-hour outage therefore takes two to four cylinders, and for emergency heat in a house the manual allows 1 lb cylinders only, so stock them. In a camper, shelter or tent, a 20 lb tank outside on a hose gives 48-110 hours and saves a lot of cylinder swaps.

The hose matters more than people expect. The manual names Mr. Heater hoses F273701, F273702 and F272702, each with fuel filter F273699 replaced every year, or the F273704 Buddy series hose, which needs no filter. Generic hoses can leach oil that gums up the heater; Mr. Heater told one owner that the F273704 is made from a rubber that doesn't use that oil. When we checked, neither the F273704 nor the F273702 had an offer on Amazon, so buy one from a Mr. Heater dealer, and buy the F273699 filter if your hose needs it. The swivel regulator is fixed at 11 in W.C., and the manual says not to reduce tank pressure to it.

Expect a long purge after hooking up a hose; the manual says lighting takes longer while air clears the line.

Reliability

The Portable Buddy's weak spot is the same as the rest of the Buddy line: a sensitive pilot. A light breeze can push the flame off the thermocouple outdoors, which the manual itself mentions as nuisance shutoffs in some wind. Indoors, a shutoff usually means not enough fresh air, and the manual's fix is to ventilate before relighting and to have it serviced if it keeps happening. Spider webs and dust in the pilot and burner are the other common cause; the manual asks you to check them periodically and warns that a blue flame rolling over the top of the tile means it needs cleaning.

Past that, it's a durable little heater. One owner whose new Big Buddy kept shutting down had used a Portable Buddy for at least ten years without that problem, and kept it along as the backup. Mr. Heater's documents disagree on the warranty: the current manual and the product page say 3 years, while the warranty-policy page and the Amazon listing say 1 year. Register it, keep the receipt and plan on the shorter term. The manual's warranty requires returning the heater at your expense with proof of purchase.

Portable Buddy, Little Buddy, Buddy FLEX or Big Buddy

The Little Buddy is for a one-person tent and nothing bigger. The Buddy FLEX can't turn down below 8,000, which is too much for a small insulated shack, and its manual rules out bedrooms and bathrooms. The Big Buddy is the one to buy for a four-person hub, a wall tent, or long cold days in wind, and it asks for twice the vent area. Our Big Buddy vs Portable Buddy comparison goes deeper on that choice.

Who it is for

Buy the Portable Buddy if you fish from a two- or three-person shelter, camp in a tent or truck cap in the shoulder seasons, take the chill off a van in the morning, or want backup heat for one room during an outage, and you'll follow the venting rules, keep it out of the room you sleep in while it runs, and carry a CO alarm. For those jobs it's the propane heater we'd buy first.

Skip it for a closed garage or shop, as your only heat in a van you live in, or for sleeping heat of any kind. And if you need 18,000 BTU on the coldest days, spend the extra on the Big Buddy.