Mr. Heater Big Buddy review
Mr. Heater Big Buddy 4,000/9,000/18,000 BTU Propane Heater (Midnight Series)
By Tom Calder
Key specs
The maker's figures.
- Heat output (max)
- 18,000 BTU/hr
- Heats up to (maker)
- 450 sq ft
- Fuel
- Propane, two 1 lb cylinders or a 20 lb tank (hose sold separately)
- Run time (maker)
- Up to 96 h on low from a 20 lb tank
- Safety shutoffs
- Low-oxygen shutoff, tip-over shutdown
Three settings up to 18,000 BTU for about 450 square feet, a fan to move the heat, and room for two 1 lb cylinders or a 20 lb tank, where Mr. Heater gives up to 96 hours on low. Low-oxygen and tip-over shutoffs are both listed. Note the listing's own line: indoor use is not approved in Massachusetts (or Canada).
- Best for
- A larger space, and the longest run on a 20 lb tank
- Skip it if
- You live in Massachusetts and want it indoors
We earn a commission if you buy through the retailer links on this page. It doesn't change our verdict. How we make money →
Researched, not used. We haven't used this product. This review is built from the maker's specifications, owner reports and our own sizing.
What we like
- Up to 18,000 BTU, about 450 sq ft
- Up to 96 hours on low from a 20 lb tank
- Low-oxygen and tip-over shutoffs
Worth knowing
- Indoor use not approved in Massachusetts
- Bigger and heavier than the Buddy
ⓘ As an Amazon Associate, PreparedStates earns from qualifying purchases. We may earn a commission when you buy through our links. When two products are close, commission can decide which one we pick. A clearly better product always wins. Amazon prices come from Amazon's own product data and can change at any time.
Our review
Mr. Heater's Big Buddy (model MH18B) is a portable propane radiant heater with three settings, 4,000, 9,000 and 18,000 BTU, for spaces up to about 450 square feet, with low-oxygen and tip-over shutoffs. Its manual allows emergency indoor heating only on disposable 1 lb cylinders and with ventilation. This review covers the rules, run times and who should skip it.
What the Big Buddy is
The Big Buddy is the larger sibling of the Mr. Heater Buddy: three heat settings instead of two, room for two 1 lb propane cylinders, and coverage Mr. Heater gives as up to 450 square feet. It weighs about 17 lb. Mr. Heater says it has an automatic low-oxygen shutoff (ODS) and a tip-over shutoff, and that on some current units the built-in fan has been removed, so check which version you are buying.
Mr. Heater lists sale restrictions for Massachusetts and Canada, and the manual says the heater is not for use in a dwelling home in California. Check your state and local rules before you buy it for a house.
The indoor rules, in the manual's words
This is an unvented heater that uses oxygen from the room. The manual says it is safe for indoor use in small recreational enclosures with means for combustion air and ventilation, and that it may be used for emergency indoor heating when connected to a disposable 1 lb propane cylinder. It requires a vent area of at least 18 square inches, for example an opening about 4 1/4 by 4 1/4 inches. Without enough air, the manual warns, it may give off excessive carbon monoxide, an odorless, poisonous gas.
Three more lines matter in a home. Never operate the heater while sleeping. Never bring a refillable propane cylinder indoors; a 20 lb tank belongs outside. Do not use other fuel-burning appliances inside at the same time.
Carbon monoxide: what the agencies say
CDC calls carbon monoxide an odorless, colorless gas that kills without warning, produced whenever fuel burns, and advises battery-operated or battery back-up CO detectors near every sleeping area. Ready.gov says to put CO detectors with battery backup in central locations on every level of your home. CPSC lists the symptoms: headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion. If anyone feels these, get to fresh air at once.
Install a CO alarm before the heater ever comes inside; see our CO alarm comparison, our carbon monoxide guide and how to stay warm without power.
Fuel and run times
The manual's rough run times depend on the setting: a single 1 lb cylinder lasts 1.5 to 6 hours, two last 3 to 12 hours, and a 20 lb cylinder 24 to 108 hours. Outdoors, or in a ventilated commercial or recreational enclosure, it can run from a 20 lb tank through a Mr. Heater hose; the manual names the approved hoses and says to fit fuel filter F273699 on them and replace it yearly, except with the Buddy series hose F273704. Mr. Heater says unauthorized accessories are prohibited and void the warranty.
It is rated up to 7,000 feet; above that, the manual says it may shut off. Mr. Heater's page lists a three-year limited warranty.
How it compares, and the verdict
On our indoor propane and kerosene heater page, the smaller Buddy tops out at 9,000 BTU for about 225 square feet on one cylinder, simpler for a single room. The Big Buddy heats a larger space and runs longer on two cylinders. Kerosene heaters such as the Sengoku HeatMate are another route, with their own ventilation rules.
Verdict: a capable emergency heater for a larger room, if you follow the manual exactly. Skip it if you would run it overnight, cannot ventilate the room, have no CO alarm, or live where indoor use is restricted.
A researched review, built from the maker's specs, manual and US listings; facts checked 2 Nov 2026. Sources: Mr. Heater: Big Buddy portable heater (MH18B); Mr. Heater: MH18B operating instructions and owner's manual (PDF); CDC: Carbon monoxide poisoning basics; CPSC: Portable heaters and camping equipment; Ready.gov: Power outages.
Who shouldn't buy this
Don't buy it if you live in Massachusetts and want it indoors: the listing says that isn't approved there.
This is a Researched review: we haven't used this product. We check every specification against at least two independent sources, re-check the US price on a schedule where we can track it automatically, and say plainly who it isn't for. Commissions never change a rating.
If this isn’t the one
Best for The classic: one living room through an outage
Read the review →Best for One small room, a bathroom or a home office
See the comparison →Best for A bit more heat than the Buddy, with tip-over protection listed
See the comparison →Questions
Is the Mr. Heater Big Buddy safe to use indoors?
Its manual allows emergency indoor heating on a disposable 1 lb cylinder, with at least 18 square inches of ventilation, a working CO alarm and someone awake. It says never operate it while sleeping.
Can I connect a 20 lb propane tank indoors?
No. The manual says never bring a refillable propane cylinder indoors. A 20 lb tank is for outdoor use or ventilated enclosures, with an approved Mr. Heater hose and fuel filter.
How long does the Big Buddy run on 1 lb cylinders?
By the manual's rough guide, one 1 lb cylinder lasts 1.5 to 6 hours and two last 3 to 12 hours, depending on the heat setting.
Can I use the Big Buddy in Massachusetts or California?
Mr. Heater lists sale restrictions for Massachusetts and Canada, and the manual says it is not for use in a dwelling home in California. Check local rules first.